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Självständigt arbete vid LTJ-fakulteten, SLU Alnarp
Hortonomprogrammet 2009-03, 15 hp, C-nivå
Individual Project at the LTJ Faculty, SLU Alnarp
The Horticultural Programme 2009-03, 15 ECTS, level C
Obtaining high quality textile fibre from
industrial hemp through organic cultivation
by
Elin Bengtsson
SLU, Sveriges Lantbruksuniversitet
Key area Agriculture - Farming Systems, Technology and Product Quality
Author Elin Bengtsson
Title Obtaining high quality textile fibre from industrial hemp through organic
cultivation
Swedish title Att uppnå högkvalitativ textilfiber från hampa genom ekologisk odling
Key words Cannabis sativa, hemp, fibre, fibre quality, fibre crop, textile fibre,
organic
Supervisor Bengt Svennersted, SLU, the Agriculture – Farming Systems, Technology
and Product Quality key area
Examinator Beatrix Alsanius, SLU, the Horticulture key area
Course title Bachelor project in the Horticultural Programme
Course code BI0492
Credits 15 hp
Level Basic C
Alnarp 2009
2
Att uppnå högkvalitativ textilfiber från
hampa genom ekologisk odling
av
Elin Bengtsson
3
4
Abstract
The urgency to find alternative fabrics to conventionally produced cotton is increasing as vast
amounts of agrochemicals are used and a lot of irrigation is required. In this literature survey
the potential of organic cultivation practices to produce highly qualitative hemp fibre, suitable
for the textile industry, was investigated. The definition of a fibre in the textile context as well
as of the qualities that are essential for a textile fibre was necessary as a base for the
discussion in this thesis. The quality parameters looked at were fineness, strength, length,
friction, and colour. The impact of external growth factors and plant development on these
quality properties are discussed. No industrial norms for hemp textile fibres are available.
However, there are guidelines available, developed for growers and processors to obtain an
even and easily processed fibre material, optimized for textile purposes. Although hemp with
high quality fibre with showed to be easily cultivated by organic means to, discrepancies in
optimal harvest time with respect to fibre quality, and legislated harvest time (being beyond
this point in time) puts the grower in a technical dilemma regarding the fibre quality.
5
Sammanfattning
Det är angeläget att hitta alternativa textilmaterial till konventionellt producerad bomull,
eftersom betydande mängder bekämpningsmedel och bevattning krävs där. Inom ramen för
denna litteraturstudie undersöktes potentialen för ekologisk odling för att producera
högkvalitativ hampafiber avsedd för textilindustrin. Definitionen för vad en fiber är i
textilsammanhang, liksom definitioner för de kvaliteter som är nödvändiga för en textil fiber
krävdes som bas för diskussionen i uppsatsen. De kvalitetsparametrar som upptogs i
diskussionen var finlek, styrka, längd, friktion och färg. De diskuteras både ur perspektivet
gällande yttre växtfaktorer och gällande växtens utveckling, som tillsammans påverkar
kvalitetsparametrarna. Industriella operativa normer för hampafiber eftersöktes utan
framgång. Däremot finns riktlinjer framtagna för odlare och processenheter för att få ett jämnt
och lättbearbetat fibermaterial, optimerat för textila ändamål. Trots att hampa visade sig vara
lättodlad i ekologisk odling för att producera fiber av hög kvalitet, så gör skillnader i
skördetid för optimal fiberkvalitet respektive den lagstiftade skördetiden att odlaren ställs
inför ett fibertekniskt dilemma.
6
Index
ABSTRACT........................................................................................................................................................... 5
SAMMANFATTNING......................................................................................................................................... 6
INDEX.................................................................................................................................................................... 7
INTRODUCTION................................................................................................................................................. 8
MATERIALS AND METHODS ....................................................................................................................... 11
RESULTS AND DISCUSSION ......................................................................................................................... 12
THE HEMP PLANT – BOTANY, ORIGIN AND CLASSIFICATION.................................................................... 12
Botany........................................................................................................................................................... 12
Origin............................................................................................................................................................ 13
Classification ................................................................................................................................................ 13
WHY GROW INDUSTRIAL HEMP?............................................................................................................ 14
BREEDING ........................................................................................................................................... 14
Genetic background and breeding objectives............................................................................................... 14
Breeding and varieties .................................................................................................................................. 15
WHAT ARE FIBRES?............................................................................................................................. 16
Fibre function and definition......................................................................................................................... 16
FIBRE QUALITY AND EXTERNAL GROWTH FACTORS ................................................................................ 17
Textile fibre quality parameters.................................................................................................................... 17
Quality guidelines ......................................................................................................................................... 19
Climate.......................................................................................................................................................... 20
Temperature.................................................................................................................................................. 20
Water............................................................................................................................................................. 20
Light.............................................................................................................................................................. 21
Soil ................................................................................................................................................................ 21
Nutrients........................................................................................................................................................ 21
GROWTH CYCLE................................................................................................................................... 22
Germination.................................................................................................................................................. 22
Vegetative growth ......................................................................................................................................... 23
Fibre formation............................................................................................................................................. 24
Flowering...................................................................................................................................................... 25
Optimal harvest time..................................................................................................................................... 26
ORGANIC HEMP CULTIVATION ............................................................................................................... 26
Organic practices and applications .............................................................................................................. 26
Plant threats and protection.......................................................................................................................... 29
Preventative measures .................................................................................................................................. 30
POSTHARVEST..................................................................................................................................... 31
Retting........................................................................................................................................................... 31
Fibre separation............................................................................................................................................ 32
Cottonisation................................................................................................................................................. 33
LEGISLATION AND RELATED AUTHORITIES ............................................................................................. 33
Legislation regarding organic cultivation .................................................................................................... 33
Legislation regarding hemp cultivation ........................................................................................................ 35
CONCLUSION.................................................................................................................................................... 36
REFERENCES.................................................................................................................................................... 38
7
Introduction
The recent focus and rising awareness on global changing climate has lead us to reconsider
our consumption patterns – not only in terms of energy and fuel use, but also about how the
things we use in our daily life are being produced, and what product is produced in a more
sustainable way than its alternatives. This also applies to the food we eat – we may soon see
CO2 emission price tags on the groceries at the mall. More and more people are also taking an
interest in the clothes they wear and the impact of their production on nature. Luckily, the
world-wide trade with organically grown crops are on a steady increase of about 15 %
annually to reach 280 billion SEK during 2007 (Ryegård, 2007). This is thanks to public
demand and legislative decisions taken at the levels of our communities, countries and
through multilateral cooperation.
In 2006 the Swedish government took a decision on 20 % of the arable land being used for
certified organic cultivation by 2010 (Jordbruksdepartementet, 2006). Industrial hemp is a
crop well suited for organic cultivation within the EU to meet the EG legislative demands.
Hemp is a good multi use alternative crop as it is able to establish quickly in the field and also
has a relatively short growing season. Plant protection measures are minimal partly thanks to
the speedy growth making it extremely weed competitive, and partly thanks to the
introduction of a new plant family, Cannabaceae, in the crop rotation (Jordbruksverket,
2007a). However it is still susceptible to plant diseases (Clarke, 1999). Hemp has also proven
to have positive effects on soil structure – one of the preconditions in organic cropping
(Jordbruksverket, 2007a).
The multiple uses of industrial hemp provide for a self-evident place on the market. Literally
all parts of the plant can be used. The fibre can for instance serve as reinforcement material in
automotive construction and furniture industry. Other markets are high quality paper and
packaging, as well as the evident use in the making of clothes and cordage. The woody inner
fibre of the hemp stalk, the hurd, can be used for animal bedding, bio mass fuel, compost,
paints and sealants, furniture, in plastics and polymers and construction products. The seeds
produce a nutritious oil which can be used in cooking and the seeds themselves are edible
(Robinson, 1996).
8
However, there are certain restrictions concerning hemp cultivation due to associating hemp
with marijuana tetrahydrocannabiol, THC, known as the psychoactive compound in drugs
made from marijuana. Only certain bred varieties of hemp containing a low level of THC are
allowed in legal cultivation of industrial hemp. Wild growing hemp and hemp for drug
production contain 3–20 % of THC (NAIHC, 1997). From a public point of view, what most
people first think of when they hear about hemp and Cannabis is the use of it as a drug.
General opinion often makes growers hesitant to try something new such as hemp despite it
being a perfectly sound crop from a modern perspective. The ban to grow hemp in Sweden
was revoked only in 2003. Growing industrial hemp within the EU today requires a specific
application for a cultivation subsidy and only listed varieties with a THC level below 0.2 %
are allowed (Jordbruksverket, 2008). Even the time of harvest is regulated – At harvest the
crop must contain more mature than immature seeds, as most pollen will then be shed, thus
preventing collection and illegal breeding (Barron et al., 2003). The seeds from an own
cultivation are not to be sown. Since 2007 hemp is classified as an energy crop
(Jordbruksverket, 2008).
Other limitations with hemp, concerning breeding, is the species being dioecious. Some
approved cultivars have been bred from naturally existing monoecious specimens and
interbred to produce uniform plants necessary for a reliable and even yield, especially for seed
production (Bócsa and Karus, 1998).
Depending on what product (e.g. fruit, oil, fibre) is desired from a plant and what part of the
plant is used (e.g. stem, leaves, seeds, root, flowers) different cultivation practices come into
play in order to optimize yield and quality. The objective of this literature study was to
investigate whether it is possible to obtain a high quality hemp stem fibre according to textile
industry standards, with respect to textile quality parameters such as fibre length, fineness,
strength, friction and colour by means of organic cultivation practices. The objective was also
to see where the possible bottlenecks and difficulties may lie, provided the afore-mentioned
production is possible. Focus is put on European preconditions. The questions initially asked
were:
• What quality parameters are present for hemp fibre and how are they defined?
• What quality standards are set by the industry for textile use of hemp fibre?
• Which growth stages are crucial in obtaining high quality fibre?
9
• What growing conditions are optimal to meet these standards and demands?
• Which are the criteria for organic cultivation in Europe and Sweden?
• Can the standards and demands be met through organic cultivation, and what special
implementations need consideration?
10
Materials and Methods
This Bachelor thesis and literature survey is based on information from current and state of
the art sources on hemp fibres and organic cultivation. Scientific reports and articles, study
reports, books and authority reports were gathered using university linked databases and
search engines on the Internet. Sources of Information were also retrieved from my supervisor
Bengt Svennerstedt at the Department of Agricultural Biosystems and Technology, Swedish
University of Agricultural Sciences (SLU).
11
Results and Discussion
The hemp plant – Botany, Origin and Classification
Botany
Cannabis sativa shown in figure 1, is an erect annual herb with palmate leaves. It normally
reaches a height of up to 5 m during a period of 4–6 months (Bócsa and Karus 1998).
Cultivated varieties in Northern and Western Europe usually grow 2.0–3.5 m tall (Bruce et
al., 2005). The primary root reaches 40–250 cm down and branches out with 60–80 cm long
secondary roots. The major part of the root mass is located at a depth of approximately 30–50
cm (Bócsa and Karus, 1998). The flower initiation response occurs when the plant is
subjected to short days of less than 12–14 h. Before that the plant grows more vigorous as a
response to increasing day length (Clarke, 1999). Hemp’s characteristic scent arises from
THC exudating glandular trichomes covering the lamina (Bócsa and Karus, 1998).
Figure 1. Left: Industrial cultivation (Wikimedia Commons, 2000). Right: Characteristic leaf of C. sativa
(Wikimedia Commons, 2008).
The species is dioecious, but monoecious specimens with both sexes on the same plant occur
in the wild and are utilised in breeding and cultivation. Just before flowering, the leaf
arrangement changes from opposite to alternate (Bócsa and Karus, 1998). Male plants
blossom before female plants and the species is wind pollinated. Until flowering is set off, the
male and female plants can generally not be distinguished other than by differently exhibited
growth patterns (Clarke, 1999). Male plants grow longer and thinner and branch out less than
female plants do (Bócsa and Karus, 1998).
12
Origin
The natural habitat where hemp first evolved is Central Asia. There it was also the first fibre
plant to be cultivated. Findings of hemp as a cultural plant in China date back to 12 000 years
ago, long before it was known in Europe (Robinson, 1996). Its introduction in Europe may
have been about 3500 years ago by nomads and later into Africa by Arab traders (figure 2)
(Hillig, 2005). This Northern path of hemp distribution to Europe went from Siberia via the
Middle East and into the Mediterranean area. From there it spread all the way to France. The
Scythians (Indo-Iranians) who branched off from the Aryans, took it further north into the
Baltic area. A later Southern introductory path was made by the Arabs, who brought in hemp
from Africa to Spain (Robinson, 1996).
Figure 2. Left: Spreading of Cannabis indica and Cannabis sativa (Hillig, 2005). Right: Northern and Southern
introductory pathways to Europe of Cannabis sativa (Robinson, 1996).
Classification
The hemp plant (Cannabis sativa L.) was originally classified by Carl von Linné in 1753
(Robinson, 1996) and belongs according to the latest classification to the family Cannabaceae
consisting of the two genera Cannabis and Humulus (Bócsa and Karus, 1998). The popular
view today as introduced by Serebriakova (1940) holds the opinion that the genus Cannabis is
separated into the two species Cannabis indica (Indian hemp) and Cannabis sativa (common
hemp) which is supported by genetic evidence from Hillig (2005). The subspecies of
Cannabis sativa are Cannabis sativa ssp. spontanea (wild hemp) Cannabis sativa ssp. culta
(cultivated hemp) (Bócsa and Karus, 1998). Cannabis sativa ssp. culta is then further divided
into four geographical races; Northern hemp, Middle-Russian hemp, Southern hemp, and Far
Eastern hemp (Hillig, 2005). The Northern type is short and yields a lot of seeds, while the
Southern type is taller, more branched and yields more fibre (Osvald, 1959).
13
Why grow industrial hemp?
Industrial hemp is a versatile crop which can be grown for many purposes; seeds for food and
oil, fibre for textiles and insulation, reinforcement in composite materials, and making paper
(Robinson, 1996). The shives can also be used for lightweight particleboard in for example
furniture and as building material (Svennerstedt, 2003). As a crop in general and fibre crop in
particular, hemp has many advantages over other crops. This applies especially to cotton
production where vast amounts of irrigation water and agrochemicals are needed. Cotton is
also restricted to growing in a sub-tropical climate while hemp thrives in moderate climate
and requires less input of water and agrochemicals for high yield which makes it a promising
crop in organic farming (Ebskamp, 2002; van der Werf, 2004). Very few insects or diseases
pose any major threats to hemp. The quick field establishment and canopy closure of the crop
makes it extremely weed competitive, especially when sown at a high density for fibre
production (Bennett et al., 2006). Provided with the right external conditions hemp does not
require much labour from the time of sowing to harvest, according to several interviewed
growers. Hemp can easily be introduced in a crop rotation having early and late flowering
varieties which are convenient with respect to preceeding or following or other more
demanding crops taking advantage of for example hemp’s deep root system which aerates and
improves the soil structure. After harvest a lot of the plant and root material can be left and
tilled in the field which also minimises loss of valuable nutrients (Barron et al., 2003).
Breeding
Genetic background and breeding objectives
Cannabis can be considered as one isolated gene pool. All populations within the genus can
intercross, but the genus is reproductively isolated from other genera (de Meijer, 1999),
however research by Hillig (2005) proves speciation between Cannabis sativa and Cannabis
indica. While still uncertain, this is probably due to human selection for fibre and seed in the
first case and for drug production in the latter case. Selection has mainly affected the fibre
content and the presence of THC. The fibre and seed varieties are bred for both high seed and
fibre yield, but also a low amount of THC, whereas the drug strains have been bred to contain
a high level of THC (Clarke, 1999). During the 1960ies and 70ies the THC content in dried
leaves varied between 1% and 3%, but intensive cultivation has given rise to cultivars with up
to 6 – 20% THC (Ashton, 2001).
14
In light of the recent rediscovery of hemp as such a multifaceted and versatile crop there is
economic incentive to, apart from breeding for fibre and seed yield, also breed for seed oil
yield and resistance to pests and diseases. In order to widen the range of habitats in which
hemp can be cultivated, it is also bred for tolerance to salt (Clarke, 1999).
Breeding and varieties
Hemp is mainly bred in Europe for the production of fibres. The objective is to maximise the
fibre yield. This can be done in two ways; the stalk yield per area unit can be increased, and
the percentage of fibre in the stalk can be increased (Clarke, 1999).
Being able to provide both fibre and seeds it is mainly the female plants which contribute to
the products of hemp and this leads us to one of the primary obstacles with breeding – it is a
dioecious species and breeding for fibre content must be based on individual plant selection
(Clarke, 1999). With the Bredemann method where a male stem is cut lengthways and its
fibre content can be determined, only the best plants are allowed to flower and pollinate
females. With this method a threefold increase of the fibre content was obtained over a 30
year period (Ranalli, 2004). The other obstacle breeders have had to overcome is hemp being
wind pollinated and intercrossing freely meaning that any potential female seed parent must
be isolated in order to control pollination (Clarke, 1999).
European breeding for increased fibre content began in the 1920s. During the 1930s the first
monoecious plants were described, constituting a foundation for the development of
monoecious varieties. The advantage with a monoecious hemp population stand over a
dioecious one is the uniformity in growth. The male and female vegetative period difference
aggravates harvest and affects fibre quality since the male plants wither and become retted
after flowering while still in the field, whereas female plants continue to mature. In the 1950s
the countries having a leading role in modern hemp breeding and genetics were the former
Soviet Union, Germany, Italy and Hungary. A decade later France started to develop their
own varieties. These are now dominating the fields of the EU. Russia has been the most
successful country in breeding for a very low THC content (Bócsa, 1999). In 1996, two
French cultivars nearly devoid of THC were registered; “Santhica 32” and “Epsilon 68” (de
Meijer, 1999). Entirely THC-free cultivars are, however, impossible to obtain since the
compound has an important but poorly understood role in plant development (Bócsa and
15
Karus, 1998). The following varieties are grown for fibre and are legally accepted in the EU
for cultivation in 2008 (table 3).
Table 3. EU’s list of approved cultivars for the year 2008 (Jordbruksverket, 2008).
Beniko Epsilon 68 Lipko
Bialobrzeskie Fasamo Lovrin 110
Cannacomp Fedora 17 Red Petiole
Carmagnola Felina 32 Santhica 23
Chamaeleon Felina 34 Santhica 27
CS Ferimon Silesia
Delta 405 Fibranova Silvana
Denise Fibrimon 24 UNIKO-B
Diana Futura 75 Uso 31
Delta-Llosa Kompolti hybrid TC Zenit
Dioica 88 Kompolti
At times when there has been a shortage of seeds, the direction of breeding has been towards
unisexual varieties (solely female plants). By pollinating the female dioecious hemp plant
with pollen from a monoecious plant it is possible to obtain a very high rate of female plants
(Bócsa and Karus, 1998).
Breeding specifically for high quality fibre is no longer an objective as refined fibre
processing techniques are available. However, comparative analyses have shown that male
hemp has noticeably better fibre quality characters than female hemp, and dioecious forms are
better than monoecious ones (Bócsa, 1999). As many products made of hemp fibre are subject
to wear and tear, the emphasis in production is now put on quality traits such as fibre length,
fineness, strength, flexibility and friction (Bócsa and Karus, 1998).
What are fibres?
Fibre function and definition
A hemp fibre yarn is shown in figure 4. In botanical terms,
fibres are described as long, straight and thin, often
occurring in bundles. Bast fibres (extraxylary fibres) are
made up from sclerenchyma cells which have thick
secondary cell walls that usually become lignified. They
have a structure constitution made to support the plant
(Mediavilla et al., 2001; Roberts, 2006). Sclerenchyma
cells are dead cells with thick lignified secondary cell walls simply blocking any transport of
Figure 4. Industrial hemp fibre yarn
(
Wikimedia Commons
,
2007a
)
.
16
water and solutes (Amaducci et al., 2005). Figure 5 explains the relationships between
different cell and fibre types.
Collenchyma cells
Non-lignified, alive
Xylary fibre
= wood tissue
Leaf fibre Pericyclic fibre
Mechanical,
supportive tissue
Sclerenchyma cells
Lignified, dead
Extraxylary fibre
= phloem or bast tissue
Hemp industrial fibre
Phloem (secondary)fibre
Thin, short
Strongly lignified
Hemp industrial fibre
Cortical (primary) fibre
Large, long
Textile use
Figure 5. Schematic illustration of the hemp textile fibre origin. Modiefied from Amaducci et al., 2005.
The main constituent of plant fibres is cellulose. In primary and secondary cell walls of hemp,
cellulose is present in the range of 10–20% and about 50%, respectively. Cotton fibres consist
up to 98% of cellulose (Mediavilla et al., 2001).
Fibre quality and external growth factors
Textile fibre quality parameters
Historically hemp has mainly been used for coarser textiles. Now, thanks to technical
advances in the fibre processing industry, hemp is also used for finer garments. The common
opinion about hemp fibres is that they are both strong and long. From a raw material
perspective low variation in properties, purity and cleanness are important for a high quality
end product (Ranalli 1999). Ranalli (1999) also discusses other quality criteria for hemp fibre
and clothing as being subject to wear and tear; brittleness, elasticity, wear resistance,
durability, absorbing capacity, thermal and fire resistance. For simplicity however, the focus
here is on fibre length, fineness, strength, friction and colour as these are the basic parameters
easy to evaluate immediately after extraction. The others will largely be affected by
processing and time.
17
Hemp fibres are relatively long, but the actual cells range from 5–55 mm in length, while the
diameter varies between 16 and 50 µm (Ranalli, 1999). The fibres are not round and uniform
in shape. Especially young plant fibres are oblong when seen in a transverse section, but they
become rounder as they mature. Young plants also produce silk-like, fine-textured, very
flexible and thin fibres. Unfortunately these fibres have proven to have poor and uneven
quality (Amaducci et al., 2005).
There are many ways to define the fibre quality, but the most important parameters when
discussing textile use are fibre length, fibre diameter and tensile strength. The length/diameter
ratio indicates the fibre strength and thereby its suitability for textile application (Amaducci et
al., 2005). Textile application requires a thin, fine fibre diameter and a high strength. The
finer the fibre, the higher is its considered value.
Textile fibres are long, thin and flexible and have
a diameter of less than 100 µm while the length
is at least 100 times that of the diameter (that is
10 mm). Clothes’ fibres should not be thicker
than 40 µm or they will feel itchy on the skin, but
fibres less than 10 µm may be too weak and
break (Östbom, 2007). To describe how the
parameters length, strength, diameter and friction
need to vary and relate to each other in order to
build up a good quality fibre for spinning and
textile use, Östbom (2007) used a circle diagram
(modified in figure 6). When, for instance, the strength is small the other sections need to be
larger and vice versa. For comparison purposes to find out what fibres are suitable for textile
application, Östbom also calculated a ratio between strength and diameter (MPa/µm) which
should be as high as possible. The standard ratio for flax fibre is 25. Compared to flax, hemp
fibres are longer and more coarse (Ranalli, 2001). The ratio does not need to be more than
12.5 for hemp fibre in a blend with cotton (Östbom, 2007).
Textile Fibre Quality Parameters
Friction
Length
Diameter
Strength
Figure 6. Should one of the textile fibre quality
parameters length, strength, diameter or friction
be small, the other ones need to be larger in
order to constitute an overall good quality fibre.
Modified from Östbom (2007).
The quality parameters diameter, shape (transverse section), maturation, and quantity of
secondary fibre all vary with factors such as plant density, harvest time, internodes and even
within the same plant portion (Amaducci et al., 2005). In crowded populations the plant will
have limited branching, develop less foliage and the stem will be thin (Clarke, 1999).When
18
looking at a hemp plant, the longer and thinner the stalks are, the higher the fibre content and
the better the fibre quality (Bócsa and Karus, 1998).
Quality guidelines
There are no standardised measures for hemp as for flax, but in an EU project, IENICA,
guidelines (table 7) have been developed for traders of hemp and flax. Colour, length and
diameter are closely related to the retting process. Under-retting will result in too coarse fibres
while over-retting makes the fibre weak which leads to fibre loss during the cleaning process.
Hemp fibre quality is often judged visually by lustre and colour. High quality fibre is lustrous
and “gives a decided snap when broken” (Ranalli, 1999). The IENICA primary class colour
standards for retted hemp are steel grey, silver grey, and light grey, whereas for unretted hemp
they are light yellow, dark yellow or green yellow. For lower classes of both retted and
unretted hemp darker nuances are accepted.
Table 7. Fibre quality parameter guidelines developed within the IENICA project. The colour codes presented
above are not true to nature but merely used to illustrate the concept and the differences in colours and nuances.
Data obtained from IENICA (2004).
HEMP STRAW Retted straw Raw straw
Colour Class 1 Light grey Light yellow
Silver grey Dark yellow
Steel grey Green yellow
Low classes Dark grey Light grey Dark grey
Green grey Light green Dark green
Brown grey Light brown
Length High classes 110-130 cm 110-130 cm
Minimum 80 cm 80 cm
Stem width Class 1 4-6 mm* 3-6 mm** 4-6 mm
2 4-8 mm* 3-8 mm** 4-8 mm
3 3-12 mm* 3-12 mm** 3-12 mm
Retting degree Class 1 90% of stems* N/A
2 80% of stems* N/A
3 <70% of stems** N/A
Health condition Class 1 >90% of stems >90% of stems
2 >80% of stems >80% of stems
3 >70% of stems >70% of stems
Moisture content <20%*** <20%***
Impurities content <15% <15%
*clothing textiles **cordage ***wet basis
The desired properties of the straw have been decided in order to provide uniform material for
the processing industry. Hemp straw should be at least 80 cm long, but 110–130 cm is
required for the higher classes. First class straw should contain no more than 10% unhealthy
19
tissue. The corresponding values for second and third class straw are 20% and 30%
respectively. The fibre strength, or tenacity, should be between 27 and 69 centiNewton/tex,
which roughly equals 270–690 MPa. The fineness preferred is less than 1.5 tex (which equals
36.9 µm), that is 1.5 g/km of yarn. For blends with cotton and chemical fibres the fibre length
should be 25–45 mm whereas in wool blends the length should be 60–120 mm, and the
fineness needs to be below 2 tex (49.2 µm). The profitability and price of hemp as a fibre crop
can vary by 100% depending on the quality of the fibre (IENICA, 2004).
Climate
Hemp is well adapted to growing in temperate regions with a mild and cool climate but will
thrive in a wide range of environmental conditions. Hemp grown to produce fibre is favoured
by a humid atmosphere (Ranalli, 1999). Even though originating from Central Asia it has
been cultivated all the way from the Equator to the Polar Circle (Haverkort et al., 1999). No
cultivars for fibre or seed exist for the tropical or subtropical regions (Clarke, 1999).
Temperature
The base temperature for leaf appearance of hemp is 1oC and 2.5oC for canopy establishment.
During spring and the initial stage after germination the seedlings can survive short periods of
frost down to -8–-10oC, but older plants only tolerate -5–-6oC (Haverkort et al., 1999). Its
rapid vegetative growth phase will start after the fifth set of leaves has appeared if the average
daily temperature reaches 16oC, approximately 35 days after germination. Under these
conditions its height can increase up to 6–10 cm/day (Bócsa and Karus, 1998). Optimal
growth is reached on sunny days with temperatures between 19 and 25oC (Bócsa and Karus,
1998), but hemp grows well also within a range of 14–27oC (Barron et al., 2003). From
germination to technical maturity, that is the full flowering of male plants, fibre hemp requires
1900–2000 growth degree days, GDD. GDD represents the accumulated average day
temperature (Bócsa and Karus, 1998).
Water
Being a highly productive crop, hemp requires 300–500 l of water per produced kg of dry
matter. A total of 500–700 mm of precipitation is needed for the whole season and 250–300
mm of water during the vegetative growth phase. The precipitation in June and July is of
particular importance as it strongly influences the yield (Bócsa and Karus, 1998). During the
first six weeks there is need for ample supply of water as the roots are still near the surface of
the soil. As they grow deeper the hemp plant will tolerate drought better (Barron et al., 2003).
20
It is important to prepare the soil well in order to satisfy the water requirement but as little as
one or two days of flooding can be detrimental to a population (Bócsa and Karus, 1998).
Heavy rain, hail or wind will however not cause much damage to a hemp crop if it is sown at
a high density (Ranalli, 1999).
Light
As reported by Ranalli (1999) the stem yield of hemp can be limited by an early flowering
date, and as hemp is a short day plant its flowering date is the first criterion to consider when
choosing an appropriate cultivar for optimal fibre production, the ideal being that no
flowering occurs before harvest. Long days, as in Northern Europe, will delay flowering but
even in tests where the day length was set to 24 h flowering was not totally prevented.
Hemp needs good light conditions and the total amount of light will affect the fibre quality to
a larger extent than it will affect the yield (Bócsa and Karus, 1998). Many other spring crops
will suffer from lack of light due to slow growth of their canopy, but this is a minor problem
for hemp as it is able to grow and establish fairly well even at low temperatures (2.5 oC for
canopy establishment) (Haverkort et al., 1999).
Soil
As expressed by Bócsa and Karus (1998), suitable fibre hemp soils are those that can give a
potential yield of 10 000 kg dry matter/ha, that is the soil needs to have good water
permeability, be well-drained, and aerated. It also needs to have high potential for
accumulating nutrients. Such soils should be rich in organic matter as for example degraded
black soils, brown redzina soils and brown steppe soils. These soils potentially yield 6 000–
9 500 kg/ha. Marshy soils that retain too much water will influence the tensile strength of the
fibre negatively (Bócsa and Karus, 1998). Being a fibrous plant, hemp is better than many
other agricultural crops at extracting heavy metals from the soil, which is why it is known for
its soil remediating properties (Ranalli, 1999). The pH level of the soil should be between 5.8
and 6.0 (Bócsa and Karus, 1998), but a pH above 6 is also acceptable (Barron et al., 2003).
Nutrients
Hemp has relatively low fertiliser demands apart from a high nitrogen, N, requirement,
especially during its rapid vegetative growth phase. If the soil is not in good condition, the
crop will benefit from added N. According to Ranalli (1999), European experiments showed
that optimal growth and a yield of 15 000 kg dry matter/ha was obtained after application of
21
175 kg mineral N/ha. Excess N may however lead to a large stalk, thin bark and reduced fibre
quality and content (Bócsa and Karus, 1998), lodging (Barron et al., 2003), leafy succulent
growth and a stem diameter too wide (Ranalli, 1999). It is important to adjust the amount of
fertilisation to the soil type and its condition. In organic cropping it is also pivotal to calculate
the amount of added N from an applied total amount of manure, since mineral fertilisers are
not allowed. Per m2, 3–5 kg of organic matter can, according to Barron et al. (2003), cope
with hemp’s high N supply requirements. Recommendations in Hungary are that half the
needed amount is applied in the field after harvest of the previous crop and before the sowing
of the hemp, and the other half is applied in the spring (Bócsa and Karus, 1998). For compost
and natural minerals the amount of the different nutrients are highly variable depending on the
components, but the percentage by weight in swine manure for example are N: 6.48 %, P2O5:
9 %, K2O: 9 %, Mg: 8 %, and Ca: 2 % (Zublena et al., 1997).
Phosphorous, (P), and potassium, (K), are also well-needed macronutrients. The P
requirement is not high, around 50–70 kg/ha, but is important with regards to some fibre
quality traits – elasticity and strength – which is why the nutrient soil availability is of high
significance (Bócsa and Karus, 1998; Barron et al., 2003). The requirement of P increases
continually throughout the vegetative phase to reach a maximum in June and July during fibre
development. It is important that P is applied such that it remains in the layers of soil where
the most roots are present. K affects the fibre quality more than P does. It is normally
recommended that K is applied in the form of KSO4, potassium sulphate, because the
chloride, Cl-, ions in potassium chloride, KCl2, are detrimental to fibre development. Calcium,
Ca, and magnesium, Mg, are normally applied to a crop rotation as a whole and to keep the
soil in good condition (Bócsa and Karus, 1998). Thanks to a lot of the hemp foliage and some
part of the stem being left in the field after harvest and retting, a considerable amount of the
nutrients can be returned and reincorporated into the soil. According to Barron et al. (2003)
this amounts to two thirds of the N, Mg and Ca applied, half the amount of K, and one third of
the P.
Growth cycle
Germination
A complete life cycle from germination via leaf and fibre formation, vegetative growth, leaf
transformation, and flowering, to mature seeds normally takes 4–6 months but may be as
short as 2 months or as long as 10 months. Approximate growth phases are shown below in
22
figure 8. The seeds are sown outdoors in the springtime and germinate after three to seven
days (Clarke, 1999). Computer models made to fit north-western Europe show that at a
density of 64 plants per m2, plant emergence occurs after 16 days when sown in mid March,
after 11 days when sown in mid April and after 7 days when sown in mid May. To maximise
the perception of photosynthetically active radiation (PAR) hemp is favoured by an early
sowing date as it grows well even at low temperatures, but the risk of frost damage must also
be taken into account (Haverkort et al., 1999).
Growth Cycle of Industrial Hemp
0
1
2
3
4
5
6
7
8
9
March April May June July Aug Sep Oct
Month
Sowing
Germination after 3-7 days
Seedling emergence after 7-16 days
Vegetative growth until flowering
Primary fibre formation before flowering
Change of phyllotaxis
Flower formation and flowering
Technical maturity (full male plant flowering)
Optimal harvest time
Figure 8. The different phases and events in the growth cycle of industrial hemp. Germination and emergence
occur 3–7 days and 7–16 days after sowing, respectively, depending on time of sowing. Vegetative growth is
vigorous during the first 2–3 months, and primary fibres for textile use are formed. Technical maturity and optimal
harvest time occurs around the peak of flowering before too stem lignification begins and too much of secondary
fibres are formed. Adapted from Keller et al. (2001) and Mediavilla et al. (2001).
Vegetative growth
Approximately 10 cm above the cotyledons the first true leaves appear. Initially there will
only be one leaflet per leaf. As the plant grows, the number of leaflets will increase to
eventually reach a number of up to 13 leaflets (Bócsa and Karus, 1998). The environmental
influences on the growth habit are strong. During the first 2–3 months the vegetative growth
will be vigorous as a response to increasing day length (Clarke, 1999). On long summer days
the growth is rapid, up to 6–10 cm/day. Under optimal conditions – that is good light
23
availability, a well-drained soil and plenty of nutrients and water – the hemp plant grows tall
and branches extensively. In a normal growth cycle of 4–6 months it can grow 5 m tall (Bócsa
and Karus, 1998). However, when given poor amounts of nutrition and little water the foliage
will be minimal and a plant can flower and give seeds when it is only 20 cm tall. The sowing
density of plants also has a profound effect on the morphology. In crowded populations
(figure 9), such as when cultivated for fibre, the plant will branch less, develop less foliage
and the stem will be thinner than the stem of a plant given more space (Clarke, 1999).
Figure 9. Left: Densely planted stand of industrial hemp. Middle: Young hemp plant (Wikimedia commons,
2007b). Right: Field after harvest. Left and right photos: Elin Bengtsson.
Fibre formation
The fibre (figure 10) for textile use is the primary fibre originating from the pericycle between
the phloem and the cortex (Amaducci et al., 2005). Primary fibres are formed and filled
during vegetative growth before flowering (Mediavilla et al., 2001). They are formed by the
apical meristem and the number of elementary fibres remains constant throughout one
internode and its vegetative phase. Along with internode elongation these sclerenchyma cells
and fibres will elongate. Immediately after elongation has ceased, formation of secondary
fibre (Amaducci et al., 2005) and cell wall lignin polymerisation take place which both
harden the stem (Mediavilla et al., 2001). During flower formation, when sowing ‘Kompolti’
at a density of 60 kg/ha and 170 plants per m2 after some thinning (a typical density for fibre
production in central Europe), Mediavilla et al. (2001) found the increase in fibre yield to be
most pronounced on the lower third of the stem, where 54 % of the fibre was located. It was
discovered in Hungary in the 1960s that there was a strong negative correlation between the
fibre content and the fibre quality. A 1 % increase in fibre content led to a reduction of the
fibre fineness that is the fibres were thinner because the increase in total fibre content was due
24
to an increase of the secondary fibres (Bócsa, 1999). At the end of flowering, when technical
maturity (full flowering of male plants) was reached, both maximum stem yield and bark
yield was obtained by due to an increase in the production of secondary fibre Mediavilla et al.
(2001). Amaducci et al. (2005) found this to be coupled with the lignification of the
secondary fibres. At this point the bark quality may decrease as secondary fibre is not wanted.
Figure 10. Upper right and upper left: Unretted and partly separated raw industrial hemp fibres directly off the
stem. Lower left: Thin fibre ends. Lower right: Broken off stem with epidermis and fibres. Photo: Elin Bengtsson.
Flowering
For flowering, hemp requires short days of 12–14 hours depending on strain, cultivar, and its
latitudinal origin. Just before flowering the leaf arrangement changes from opposite decussate
to alternate and remains so throughout the growth cycle. Also the size and number of leaflets
per leaf decreases until there is only one small leaflet under each pair of flowers. Male plants
have a more rapid leaf transformation than female plants, and they also increase faster in
height during vegetative growth than female plants. Apart from that, it is difficult to
distinguish between the sexes before flowering (Clarke, 1999).
25
Male flowers hang in long branched clusters while the female flowers and situated two by two
in the axils of the leaves on the central stem. Hemp is anemophilous, wind pollinated, and
after the pollen is shed the male plant dies. The female plant may continue to mature up to 5
months if pollination is sparse (Clarke, 1999). Early flowering cultivars such as the French
and Hungarian ones flower in August. During the following weeks in September stem growth
is slowed down and eventually stops, making this the optimal time for harvest of these
cultivars. Later flowering cultivars will also continue to have stem growth for a longer period
of time (Haverkort et al., 1999). Seeds are mature 3–6 weeks after pollination and drop to the
ground if not collected. Fresh seed viability is nearly 100 % but it quickly decreases with age.
After 3–5 years of storage at room temperature seed viability will have declined to 50 %
(Clarke, 1999).
Optimal harvest time
There are various methods used in helping to determine harvest time. Some growers go by
calendar date, some by stem colour, and others by drop of internode leaves or crop growing
stage. Deciding when to harvest is crucial in obtaining both high fibre yield and optimal
quality (Bócsa and Karus, 1998). Lignin plays an important role in the plant defence
mechanism against pathogens, but with respect to retting it is difficult to digest both
chemically and enzymatically. In order to obtain high quality fibre it is important to find a
harvest date where the amount of lignin is as small as possible. Mediavilla et al. (2001) found
the optimal harvest time with respect to lignin to be during the vegetative phase just before
flowering. The dilemma is that a harvest at this time is prohibited by law. At least 10 days
need to pass after flowering or alternatively the seeds must be mature (Jordbruksverket,
2008). This is to prevent the grower from collecting pollen for breeding purposes. However,
investigating optimal harvest time of unretted hemp, Keller et al. (2001) concluded that
harvest in the beginning of seed maturity was optimal for easy separation of fibres from
shives and bark.
Organic hemp cultivation
Organic practices and applications
During the last few decades when hemp has been grown in Eastern European countries, it has
been cultivated just like any other crop, in a conventional manner (Bócsa and Karus, 1998).
There, custom practice has been to use chemical defoliation before harvest as the foliage takes
26
up too much space when baling and also provides excellent breeding ground for bacteria
during the customary water retting process which was never really adopted by Western
Europe where instead field retting was employed. Due to cutting the stems in 50-60 cm long
pieces without chemical defoliation, field retting is made quicker and easier (McPartland,
1999). The interest for organic cultivation practices arose in Eastern Europe only after the
demand for organic hemp increased in Western Europe. In France, England, Germany, and
the Netherlands hemp plantations are rarely chemically treated. The costs are normally higher
than what the return is for the increase in yield after treatment, making it unnecessary. Also, a
higher market value is obtained from uncontaminated material (Bócsa and Karus, 1998).
In conventional growing systems where synthetic fertilisers and agrochemicals are used many
of the threats of soil nutrient depletion, weeds, pests, and diseases are easily overcome. But on
an organic farm where synthetic substances are not allowed, these threats are very much the
reality and other forms of control need to be employed (Barron et al., 2003).
When deciding to grow organically the first aspect normally considered is the crop rotation.
Sustainable crop rotations as seen from an organic viewpoint take things such as location and
climate into consideration. Fibre hemp has been unanimously recommended to follow a grass
or legume based ley and to precede cereals (Barron et al., 2003; Bócsa and Karus, 1998). The
medium to high N levels required by hemp is partly provided by the ley which normally is
clover or some other leguminous crop (Barron et al., 2003). An additional 80–120 kg of N/ha
in the form of liquid manure and dung from stables, make up for the rest. In fact, this is
perfect for hemp which prefers the nutrients being released gradually (Bócsa and Karus,
1998). Since good crop rotations alter between nutrient demanding and nutrient replenishing
crops, hemp’s relatively high demand with respect to giving and taking might be considered
as less advantageous. An outbalancing factor though, is that hemp also provides a high
biomass return from roots, leaves and stubble residues after harvesting. From the leaves and
stem left in the field after harvest, 20–25 % of the removed nutrient amount can be returned
for nitrogen, phosphorous, potassium, magnesium and calcium (Barron et al., 2003). In
addition, the up to 2 m long and deep-penetrating roots have a beneficial impact on the soil
structure, improving both the aeration and water balance. Hemp also contributes to a reduced
risk of nitrogen leakage and eutrophication, as this is prevented when residual nitrogen is
taken up by the roots from the deeper soil layers. Apart from building soil structural stability
and fertility, the crop rotation also includes the improvement of biological activity with a
27
thriving soil fauna (Barron et al., 2003; Bócsa and Karus 1998). There have been many
reports on increased yields in winter wheat preceded by hemp (Bócsa and Karus, 1998).
Weeds are seldom a problem in fibre hemp plantations. This is primarily due to two factors.
The first one is that hemp for fibre use is sown densely, leaving little space for weeds to
establish. The second is that hemp itself establishes and grows very quickly, and those few
weeds that have emerged are soon shaded by hemp as its canopy closes. Most weeds will
never mature under these conditions, which is why hemp serves as a truly remarkable weed
break and no herbicides are required. This is highly favourable in organic as well as
conventional cropping systems. Noteworthy is also that hemp is extremely sensitive to
herbicides and herbicidal residues – something the conventional grower needs to consider
when sketching the crop rotational scheme (Bócsa and Karus, 1998).
In Germany, tests on hemp textiles are regularly carried out by control agencies to make sure
there are no harmful substance residues. Standards are normally set to match cotton, flax and
wool. Hemp plantations are however commonly treated with pesticides for cotton, thus easily
detected. Although testing negative, the lack of detection does not prove pesticide-free
cultivation. The hemp fibres are far from as exposed as cotton fibres. Firstly, the fibres are
well hidden within the bark and never directly subjected to anything sprayed onto the plant.
Secondly, hemp fibres have a supportive rather than transportive function in the plant and
therefore they do not absorb pesticides (Bócsa and Karus, 1998).
The hemp qualitative traits as an organically grown crop are even more extensive than
previously mentioned. It has low susceptibility to diseases and pests and is fairly tolerant to
the most common ones when attacked or infested (Barron et al., 2003), or as McPartland
(1999) puts it “Hemp is pest tolerant, not pest-free” as many seem to believe. The low
frequency of fields nearby with closely related crops where pest and disease could linger and
spread is one of the reasons behind hemp’s low susceptibility to these. During all growth
stages hemp is a low-maintenance crop. What do require some effort are the harvesting and
retting processes. Coming from a family previously unintroduced in the crop rotation, hemp
also favours biodiversity on the larger scale. Barron et al. (2003) point out that in organic
farming systems profit is not always the self-evident and primary objective. Measuring all the
advantages with this cropping system in economical terms is not feasible, nor desirable.
However, considering hemp being a short cycle crop it provides good return.
28
Keeping a holistic view, McPartland (1999) sheds light over the outlook and
interchangeability of hemp as a crop grown for textile purposes. “The substitution of cotton
with hemp in the textile industry would lead to considerable ecological advantages during the
cultivation and harvesting stages. The reduction in primary energy consumption and
emissions would be about three times per each ton of fibre.”
As noted earlier, hemp is not pest free. In fact, many diseases and pests find hemp an
attractive crop, but the damage is often limited and does only rarely cause severe yield losses.
Since fibre hemp grows in dense plantations and canopy closure occurs early, insects are
attracted to the protective environment. High humidity also predisposes stalks and leaves to
fungal diseases. So far, more than 300 insect species attacking hemp are described in the
literature (McPartland, 1999).
Plant threats and protection
There is a plethora of leaf damaging insects infesting hemp; caterpillars, leaf miners, aphids,
whiteflies, leafhoppers, mealy bugs, scales and thrips (McPartland, 1999). The insects
attacking hemp may be many, but few are a serious threat. The hemp flea beetle (Psylliodes
attenuata Koch) occurs primarily in Eastern Europe. The larvae feed on the cotyledons and
the hypocotyl, and later on on developed leaves so that the plant growth rate is slowed down.
The hemp borer (Grapholita delineana) feeds as a larva on top leaves. After pupation the
larvae feed from the cavity of the stem and the more tender parts. The fibres from infested
plants do not meet industry standards and the fibre yield is also lower. The European corn
borer (Ostrinia nubilalis) affects primarily eastern and south-eastern Europe. Its caterpillars
make holes in the stem causing them to break in the wind (Bócsa and Karus, 1998).
The biocontrol methods for insect pests are mainly other predatory insects or parasitoids.
Trichogramma wasps are parasitoids which have been used successfully against the European
hemp borer. To the grower’s discontent they are not limited to stay within the boundaries of
the field. Fortunately there are alternative options, for instance microbial pesticides with
bacteria, viruses, protozoans, or nematodes. Bacillus thuringiensis is a favourite against
caterpillars, beetle larvae and maggots. The Nuclear polyhedrosis virus is sometimes used
towards caterpillars and borers. These microbial pesticides are easily mixed with water and
sprayed onto the foliage. They are also specific and the only drawback is they need to be
29
ingested by the pest to work which means they do not affect insects with sucking mouthparts.
Those insects will instead be combated by the application of fungi. Other measures of control
are soap and oil which suffocate small insects. Organically approved plant derived pesticides
are also on the market (McPartland, 1999).
In addition a number of colourful leaf spots occur on hemp; white, black, brown, yellow and
olive leaf spots. Mildews occur in the forms downy, powdery, and black mildew (McPartland,
1999). Hemp rust (Melampsora cannabina) attacks the fibre in the plant. A thiocarbamate
solution can be applied in conventional cultivation, but its high aqueous toxicity renders it
unsuitable for sites with erosion or runoff (Bócsa and Karus, 1998). Fungal attacks easily
occur after pest infestations but are rare as epidemics. Grey mould (Botrytis cinerea)
particularly occurs on hemp in Western Europe where humidity and temperatures are high
(McPartland, 1999). The plants break and fall over. During field retting stalks can be attacked
if subjected to recurrent rainfall. A good crop rotation and resistance breeding serve as the
two best control methods since the cost of fungicides does far from compensating for the
relatively higher price of organic hemp. Pythium debaryanum thrives in wet and poorly
aerated soils. It will attack seeds and sprouting plants and cause plantlets to topple over, but is
easily prevented if the field water balance is improved. Hemp canker (Sclerotinia
sclerotiorum) grows under the same preconditions as Pythium but attacks the roots, causing
the plant to dry out and die (Bócsa and Karus, 1998).
Many types of nematodes occur on hemp. Although there is no successful treatment, resistant
plant varieties are available (Bócsa and Karus, 1998).
The only weed of importance is a root parasitic plant, broomrape (Orobanche ramosa), but it
only appears in hemp seed plantations with Chinese varieties, and there are resistant varieties
available (Bócsa and Karus, 1998). Hemp can also be infected with bacteria or viruses, but
biocontrol is less efficient against these disease organisms and fungi.
Preventative measures
Preventative cultural and mechanical control usually has good effect, making the environment
unfavourable for pathogen and pest survival. This includes tillage, destruction of infested crop
residues, and maintaining a good water and nutritional balance throughout the growing
season. The use of resistant varieties and keeping a good crop rotation are key factors to
30
keeping the plantation devoid of pest organisms. Curative methods such as steam sterilisation
of the soil can be used against nematodes. The approach with sex pheromone insect traps has
been successful against both European hemp borer and hemp borer moths (McPartland,
1999).
Postharvest
Retting
Release of the hemp bast fibres from the stem is done by separation of them from the woody
core, to which they are attached by pectin, a glue-like substance made up from galacturonic
acid units. The chain of postharvest processes to attain high quality hemp fibre normally
begins with retting, but fibre separation can also be done mechanically with unretted stalks
(Östbom, 2007).
Retting is a natural degrading process where the pectic substances holding the fibres in place
are subjected to and broken down by fungi, bacteria or enzymes (Ranalli, 1999). Without
retting, there can be significant fibre loss during the subsequent refinement processes (Bócsa
and Karus, 1998).
Water retting is a method where stalk bundles are submerged in water. Normally the bundles
are placed in streams, tanks or ponds and left for about 10 days (Ranalli, 1999). Warm water
of 30–34oC shortens the process to 4 days (Osvald, 1959). The water becomes highly rich in
bacteria degrading the pectin. From an ecological point of view this type of retting is not a
sustainable method as it uses vast amounts of water and also leaves the water deficit of
oxygen and with a high concentration of bacteria that risk polluting the environment (Ranalli,
1999). However, when comparing this retting process with other types, Östbom (2007) found
that water retting gave the best fibre quality when visually determining the quality parameters
length, colour and smoothness. But water retting also seemed to have a more pronounced
thinning effect on the diameter of the fibres, than did field retting.
Dew- or field retting usually takes about 2–3 weeks and is completed when the hemp fibres
are easily separated from the bark when the stem is bent. The hemp stalks are simply left in
thin piles in the field after harvest for exposure to rain and dew (Bócsa and Karus, 1998). For
uniform retting they are turned over once or twice. Preferably the crop should be homogenous
with regard to height and stem thickness too (Ranalli, 1999). Both field and water retting
31
traditionally require a lot of manual work (Keller et al., 2001). Winter retting is taking
advantage of the natural fluctuations of temperature and humidity over the course of the entire
winter. The harvest is not done until springtime and the result is easy-to-handle already dried
and separated stalks (Östbom, 2007). In some cases herbicides are applied to the crop which is
left to dry standing. This method called stand retting takes longer than dew retting since there
is no contact with the soil to provide any moisture (Barron et al., 2003). Enzymatic retting is
also commonly performed in tanks with the addition of pectin degrading enzymes into the
water (Östbom, 2007). According to Barron et al. (2003) it is an environmentally friendly
method which gives good quality fibre which is strong yet fine. Ultrasonic retting and steam
explosion are physical methods used to minimise the fibre damage. These however, together
with chemical retting processes, have high chemical and energy input and are costly (Keller et
al., 2001).
Drying is important to halt the retting process (Ranalli, 1999). Over-retting adversely affects
fibre thickness and leads to discolouration of the fibres which turn dark grey or brown
(Östbom, 2007). Under-retting where the humidity is not sufficient can also lead to reduced
fibre quality (Barron et al., 2003).
Unretted dry green hemp stalks can be decorticated mechanically without any profound effect
on the tensile fibre strength if harvested at the right time. An optimal harvest time at the
beginning of seed maturity was determined for the variety ‘Kompolti’ by Keller et al. (2001).
Fibres from unretted hemp stalks become cheaper since the handling time is shorter. They
also contain a lower degree of microorganisms and do not require bleaching, which is more
environmentally safe (Östbom, 2007).
Fibre separation
Once retting is completed and the stalks are properly dried, the fibres need to be separated.
The process is mechanised and the stalks are passed between rollers which break the stems.
Thereafter the fibres are separated from the woody core. This procedure is called scutching
and can be done either by beating the stalks, or by passing the stems trough blades rotating
parallel to the fibres. The blades cut close to the fibres and the shives and short fibres are
discarded. The final element before the fibre can be spun, is combing or “hanckling” it to
further parallelise the fibres. After this treatment the fibres are soft and shiny and ready for
spinning (Ranalli, 2001).
32
Cottonisation
Cottonisation of coarse and very long hemp fibres can be done to make them attain quality
characteristics similar to that of cotton. Shorter hemp fibres are obtained from splitting up the
long tow gained in the regular fibre separating process. This is for the most part necessary
when the fibre is intended for garment textile use. The process makes the fibres soft and
adaptable to be combined with other short fibres and spun on cotton spinning machines
(Östbom, 2007).
Legislation and related authorities
Legislation regarding organic cultivation
The Nordic definition of organic farming was passed by the Nordic department of the
International Federation of Organic Agriculture Movements (IFOAM) in 1989. IFOAM is an
international umbrella organisation with around 700 member organisations and institutes. One
of its main tasks is to facilitate for producers consumers and intermediaries by setting up
uniform regulations regarding production, processing and trade (Sandskär, 2005). IFOAM’s
definition of organic farming is described here. Organic farming regards a self supporting,
sustainable agro-ecosystem in balance. The system is based, as far as possible, on local and
renewable resources. A key difference between organic and conventional farming is the view
on purchased means for production. For the conventional grower the only aspects of
importance are the business administrative and economical aspects, whereas the organic
grower has the limitation to base his cultivation on the prerequisites of the location. This
limitation means there is strong incentive for the organic grower to minimise nutrient losses
where they can be influenced (Jordbruksverket, 2007b).
For member countries of the EU, the council’s regulations serve as the basis for organic
production, but countries and organisations are allowed to have further restricted
arrangements (Sandskär, 2005). The EU regulations comprise production, processing, storage
and import of organically manufactured agricultural products and foodstuffs. There are also
regulations about the control, labelling, and marketing of organic products (Jordbruksverket,
2007a).
The EU has a set of requirements which must be met by any organic grower. Firstly, the
cultivation must be carried out within a varied and balanced crop rotation. The soil fertility
and biological activity also need to be sustained or improved by one or several measures
33
comprising cultivation of leguminous leys, green manure or plants with a deep root system.
Tillage of the soil with the addition of organic material derived from an organic farm, or
addition of manure and other by-products from organic husbandry will also enhance the soil
quality (Jordbruksverket, 2007a).
In Sweden, the Swedish Board of Agriculture, Jordbruksverket, is the authority with the
overall responsibility for organic production and handling. There are also two control organs,
KRAV and SMAK performing the actual control on the farms and certifying the produce as
organic. These are both authorised by IFOAM as control organs, and KRAV’s regulations are
based on those set by IFOAM (Sandskär, 2005).
There are a number of regulations to follow as an organic grower. To begin with, there must
pass a certain amount of time between growing as a conventional farmer and growing as an
organic farmer. When it concerns annual plants, such as hemp in this case, this period is 2
years. Until 2 years have passed the produce can be neither labelled nor marketed as organic.
Genetically modified organisms (GMOs) are totally prohibited, as well as any products
derived from GMOs. Even seeds need to come from plants which have been grown
organically for at least one generation (Jordbruksverket, 2007a).
For plant protection purposes one or several steps have to be taken into action to prevent the
crop from being damaged by pests, diseases or weeds. Again the crop rotation and the order
of the crops are central issues as well as choosing appropriate species and varieties.
Mechanical processing, flaming of the soil surface, and use of traps and capture bars serve as
good preventative measures. It is also essential to favour or sometimes even plant out the
natural enemies of the pests. Occasionally, these methods will not suffice and the need for
curative methods may arise. In the “EU regulations for organic cultivation” booklet there is a
list of products with their active substance given. These may be used in exceptional cases
(Jordbruksverket, 2007a).
Another list which may become of use is their list of manure and soil improving products in
case the basic measures do not make the soil fertile enough. Each product is accompanied by
preconditions. For example; the need has to be confirmed by the organ controlling the organic
cultivation. Potassium salt (KSO4) and raw phosphates are two examples of additive nutrients
on the list (Jordbruksverket, 2007a).
34
Legislation regarding hemp cultivation
A decision is taken annually as to which varieties of industrial hemp are allowed within the
EU. The criterion for being on the list is that the level of THC must never exceed 0.2 % of the
weight in any test, or else the variety will be discarded from the list of approved ones.
When it comes to growing industrial hemp in Sweden it is mandatory to apply for a financial
support, “gårdsstöd”. If this is not done, the cultivation will be considered illegal for narcotic
purposes. However, in order to actually receive the financial support, several criteria must be
fulfilled.
• The variety has to be on the list of approved varieties, and the cultivation field needs
to be within the borders of Sweden.
• Hemp seeds need to be certified and sown solely.
• The label from the seed package needs to be sent in to the Swedish Board of
Agriculture before a specific date.
• Harvest must be carried out at earliest after seed maturation or 10 days after flowering
has ended.
• Also, some special preconditions need to be fulfilled, “tvärvillkoren”.
o All agricultural land must be managed in an environmentally friendly way to
preserve the land in good condition.
o Swedish legislation aiming at achieving positive effects on environment,
human health, and plant and animal protection must be followed
(Jordbruksverket, 2008).
The time of harvest regulated at the EU level (earliest 10 days after the end of flowering)
sometimes poses a problem to the farmer. To ensure pollen is not collected at harvest for
illegal breeding purposes, there need to be more mature than immature seeds. But stem
growth is completed already at the time of seed production. Later harvest will cause stems to
be more lignified than what is optimal for the decortication and following fibre separation
processes. It may also hinder the farmer from sowing the subsequent crop at an adequate time
(Barron et al., 2003).
35
Conclusion
Obtaining a good quality hemp fibre for the textile industry by organic means requires good
planning all the way from choosing the right cultivar to the postharvest processing of the
fibre. This includes deciding on location, practices throughout the cultivation period, being up
to date with the plant stand development, harvesting at the very right moment and finally
choosing an appropriate retting method, all in order to produce a fibre with the desired
characteristics.
Despite all advice given, hemp is a low maintenance crop easily cultivated for textile fibre
production in an organic way. The major problem is being unable to harvest at a time when
the primary fibre quality is at its best and the decortication processes does not negatively
influence the fibre quality. However, thanks to postharvest retting techniques and processing a
lot can be done to make the fibre soft and applicable for use in garments.
Although no official standards are set by the textile industry for hemp fibres as those for flax,
there are guidelines provided by the IENICA project. When looking at the textile fibre quality
parameters length and diameter, the desired values are >10 mm and <100 µm. Fine fibres are
highly valued. The hemp natural fibre diameter varies between 16 and 50 µm, but since fibre
suitable for garments should have a diameter of <40 µm, I suggest this as the higher limit in a
standard for hemp fibres used for garments. The IENICA guidelines also recommend a fibre
strength of between 270 and 690 MPa. The strength largely depends on the fibre diameter, at
least up to a certain diameter after which the increase in strength levels off. The higher the
strength/diameter ratio of the fibre is, the more likely it is that it will constitute a textile fibre
of high quality. It seems clear that a hemp standard ratio very well could be set higher than
12.5 (as suggested for a blend with cotton) since such a low ratio often is the result of a fibre
coarser than 40 µm. Considering the Östbom trials where fibres appear coarser and weaker as
compared to other hemp fibre studies, a hypothetical minimum ratio which I set to 15 gave a
diameter range of ~22–37 µm. Peak ratios of 18,19 and 20 were obtained at diameters of
~23–26 µm and fiber strengths from ~440–490 MPa, so possibly for high class thin fibre and
high strength, the ratio could be even higher than 15. My personal suggestion for a strength
minimum is 300 MPa to allow for thin fibres of ~20 µm and a ratio of at least 15.
36
Unfortunately, peak values in strength above 520 MPa invariably seems to result from a fibre
that is coarser than 35 µm, i.e. close to the suggested upper limit for the fibre diameter.
Recovering the quality guidelines developed within the IENICA project were as far as I could
reach in trying to find quality standards from the industry point of view, for hemp fibre
intended for textiles. However, it was satisfying to find that the IENICA guidelines for
uniform material were easily attainable by either cultivation method, organic or conventional.
Hemp showed to be not only suitable but excellent as a crop in organic cultivation. I was able
to look at the different growth stages and specific organic practices that are crucial in
obtaining a fibre of optimal quality for processing. Even though several quality parameters of
hemp fibre can be influenced by cultivation practices, the fine fibre quality required by the
industry for the fabrication of garment textiles turned out to be largely a matter of postharvest
processing techniques. My view today is that despite hemp fibre being slightly tricky to
process, hemp has great potential in meeting future demands of crops and growing practices
adapted to be more environmentally friendly. If there had been more time for this study I
would have liked to also look at quality comparisons with other types of plant fibre that are
used in garments as well as their growing techniques and implementations from an
environmental point of view.
37
References
Amaducci, S., Medeghini Bonatti, P. and Pelatti, F. (2005). Fibre development in hemp
(Cannabis sativa L.) as affected by agrotechnique: preliminary results of a microscopic study,
Journal of Industrial Hemp, Vol. 10(1) p. 31-48.
Ashton, C. H. (2001). Pharmacology and effects of Cannabis: a brief review, British Journal
of Psychiatry, Vol. 178 p. 101-106.
Barron, A., Coutinho, J., English, A., Gergely, S. and Lidouren, E. (2003). Integrating
hemp in organic farming systems – A focus on the United Kingdom, France and Denmark
[online]. Available from:
http://www.kursusinfo.life.ku.dk/Kurser/250069/presentation/~/media/Kurser/IJV/250069/int
egrting_hemp.pdf.ashx. [2007-06-30]
Bennett, S. J., Snell, R. and Wright, D. (2006). Effect of variety, seed rate and time of
cutting on fibre yield of dew-retted hemp, Industrial Crops and Products, Vol. 24 p. 79-86.
Bócsa, I. (1999). Genetic improvement: Conventional approaches. In: Ranalli, P (Ed.)
Advances in hemp research. 153-184. New York: The Haworth Press, Inc. ISBN 1-56022-
872-5.
Bócsa, I., and Karus, M. (1998). The Cultivation of Hemp: Botany, Varieties, Cultivation
and Harvesting. Nashville, Vaughan Printing.
Bruce, D.M., Hobson, R.N., Hamer, P.J.C. and White, R.P. (2005). Drying of Hemp for
Long Fibre Cultivation, Biosystems and Engineering, Vol. 91(1) p. 45-59.
Clarke, R.C. (1999). Botany of the Genus Cannabis. In: Ranalli, P (Ed.) Advances in hemp
research. 1-19. New York: The Haworth Press, Inc. ISBN 1-56022-872-5.
de Meijer, E.P.M. (1999). Cannabis germplasm resources. In: Ranalli, P (Ed.) Advances in
hemp research. 133-151. New York, The Haworth Press, Inc. ISBN 1-56022-872-5.
Ebskamp, M.J.M. (2002). Engineering flax and hemp for an alternative to cotton, Trends in
Biotechnology, Vol. 20(6) p. 229-230.
Haverkort, A.J., Mathijssen, E.W.J.M. and van der Werf, H.M.G. (1999). Crop
Physiology of Cannabis sativa L.: A simulation Study of Potential Yield of Hemp in
Northwest Europe. In: Ranalli, P (Ed.) Advances in hemp research. 85-108. New York: The
Haworth Press, Inc. ISBN 1-56022-872-5.
Hillig, W.K. (2005). Genetic evidence for speciation in Cannabis (Cannabaceae), Genetic
Resources and Crop Evolution, Vol. 52 p. 161-180.
IENICA, Interactive European Network for Industrial Crops and Applications (2004).
Fibre facts - A framework for buyers and sellers of flax and hemp fibres within the EU
[online]. Available from: http//www.ienica.net/marketdatasheets/fibresmds.pdf [2007-04-19]
38
Jordbruksdepartementet (2006). Ekologisk produktion och konsumtion – Mål och
inriktning till 2010. Skrivelse 2005/06:88. Stockholm.
Jordbruksverket (2007a). EG:s regler för ekologisk odling, Jordbruksverkets handbok
[online]. Available from:
http://www.sjv.se/download/18.1ee2ea81117a7a944180001637/VG5-3Jordbruksv_vagled.pdf
[2007-05-10]
Jordbruksverket (2007b). Ekologisk produktion [online]. Available from:
http://www.sjv.se/amnesomraden/vaxtmiljovatten/ekologiskproduktion/definitioner.4.145865
71043c6e11ac8000108.html [2007-03-30]
Jordbruksverket (2008). Gårdsstöd and Tvärvillkoren [online]. Available from:
http://www.sjv.se/amnesomraden/stodtilllandsbygden/allastodformer/gardsstodet/odlingavha
mpa.4.2136c610a3b62996e80001818.html [2007-05-15]
Keller, A., Leupin M., Mediavilla, V. and Wintermantel, E. (2001). Influence of the
growth stage of industrial hemp on chemical and physical properties of the fibres. Industrial
crops and products, Vol. 13 p. 35-48.
Mediavilla, V., Leupin, M., and Keller, A. (2001). Influence of the growth stage of
industrial hemp on the yield formation in relation to certain fibre quality traits. Industrial
crops and products, Vol. 13 p. 49-56.
McPartland, M. (1999). A survey on hemp diseases and pests. In: Ranalli, P (Ed.) Advances
in hemp research. 109-131. New York, The Haworth Press, Inc. ISBN 1-56022-872-5.
NAIHC, North American Hemp Council (1997). Hemp facts – Scientific facts [online].
Available from: http://www.naihc.org/hemp_information/hemp_facts.html [2007-05-14].
Osvald, H. (1959). Hampa, Cannabis sativa L. In: Åkerns nyttoväxter. 574-584. Stockholm:
AB Svensk Litteratur.
Ranalli, P. (1999). Agronomical and physiological advances in hemp crops. In: Ranalli, P
(Ed.) Advances in hemp research. 61-84. New York: The Haworth Press, Inc. ISBN 1-56022-
872-5.
Ranalli, P. (2004). Current status and future scenarios of hemp breeding, Euphytica, Vol. 140
p. 121-131.
Roberts, A. (2006). Glossary – Tissues and cell types of the plant body. Available from:
http://www.uri.edu/cels/bio/plant_anatomy/glossary.html#wood [2007-07-27]
Robinson, R. (1996). The great book of hemp. Vermont: Park Street Press. ISBN 0-89281-
541-8.
Ryegård, C. (2007). Ekologiska världsmarknaden växer med 35 miljarder årligen [online].
Available from: http://www.ekoweb.nu/ [2007-05-10]
39
Sandskär, B. (2005). Växtskyddsmedel i ekologisk odling. Jordbruksinformation Vol. 5, p.1-
62. ISSN 1102-8025.
Serebriakova, T. I. (1940) V. Fiber Plants Part 1. In: Wulff, E.V. (Ed.) Flora of cultivated
plants. Moscow and Leningrad: State Printing Office.
Svennerstedt, B. (2003). Plant fibres in sustainable construction, Specialmeddelande, Vol.
243, p 1-47. ISSN 1104-7321.
van der Werf, H. M. G. (2004). Life Cycle Analysis of field production of fibre hemp, the
effect of production practices on environmental impacts, Euphytica, Vol. 140 p. 13-23.
Wikimedia Commons (2000). Cultivation of industrial hemp for fiber and for grain [online].
Available from: http://commons.wikimedia.org/wiki/Image:Industrialhemp.jpg
[2008-11-16]
Wikimedia Commons (2007a). Marijuana plant [online]. Available from:
http://commons.wikimedia.org/wiki/Image:Marijuana_plant.jpg [2008-11-16]
Wikimedia Commons (2007b). Stem fibres [online]. Available from:
http://commons.wikimedia.org/wiki/Image:Hennepvezel_Cannabis_sativa_fibre.jpg [2008-
11-16]
Wikimedia Commons (2008). Cannabis sativa [online]. Available from:
http://commons.wikimedia.org/wiki/Image:Cannabis_sativa01.jpg [2008-11-16]
Zublena, J.P., Baird, J.V., and Lilly, J.P. (1997). Nutrient content of fertilizer and organic
material [online]. Available from: http://www.soil.ncsu.edu/publications/Soilfacts/AG-439-
18/ [2009-03-25]
Östbom, G. (2007). Hampa ett textilt material – Undersökning av styrka och finlek hos
gotländsk hampfiber. Master thesis 2007:7.2. Institutionen Textilhögskolan, Högskolan i
Borås.
40
