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Quality improvement of cacti and succulents with alternative
substrates
Domenico Prisa
CREA Research Centre for Vegetable and Ornamental Crops, Council for Agricultural Research
and Economics, Via dei Fiori 8, 51012 Pescia, PT, Italy
Email:
domenico.prisa@crea.gov.it
Keywords: zeolites, cacti, propagation, chabasite, quality improvement
Propagation substrates
The soil performs fundamental functions for the support of the root system. It consists of degraded
rocks, water, air, organic substances and is formed as a result of chemical, physical and biological
actions. In the soil can take place both the germination of the seeds, but also the formation of new
plants through agamic methods, such as cuttings, or the buds, the division of the tufts, rhizomes,
tubers. In the soil there are exchanges and reactions between the elements and there are nutrients
that the roots can only use if dissolved in water.
Soil weaving
- coarse sand: 2 to 0.2 mm
- fine sand: 0,2 to 0,02 mm
- silt: from 0,02 to 0,002
- clay: less than 0,002 mm
The term structure refers to the spatial arrangement of particles and their aggregation.
Propagating substrate means "any material or combination of materials used to provide support,
moisture, ventilation and nutrients during the plant propagation process". At present, a propagation
substrate in modern nurseries must have: lightness, manageability, uniformity, absence of
pathogens, or of seeds of weeds and other contaminants.
Many propagation substrates are characterized by the mixture of various components, each of which
is able to determine particular properties. Only two components can be used to give a substrate the
right properties, which simplifies preparation. Among the most used organic materials are peat,
coconut fibre, bark, wood by-products, compost. Inorganic materials include sand, perlite,
vermiculite, polystyrene, rock wool and zeolites.
The characteristics of a propagation substrate (Iapichino, 2012)
Provide a propagation substrate
For the propagation of seeds and cuttings, the substrate must give the plants the possibility of
anchoring and support, until transplanting into pots. The apparent specific gravity or apparent
density of a substrate represents the solid component, expressed as its dry weight per unit of
apparent volume (g/cm-3). A good substrate should have an apparent specific gravity of 0.50 (g/cm-
3), be stable and maintain its characteristics in the period between the beginning of the propagation
phase and the production of the new plant. Normally it consists of a 30% solid part and the
remaining 70% of empty spaces (total porosity).
Porosity
In order to germinate the seeds or to allow the radical development, it is advisable that in the
substratum there is a good aeration. It is therefore appropriate that carbon dioxide, which is harmful
both to seed plants and to young cuttings, should be able to spread rapidly. The empty spaces of a
substrate (total porosity) represent the volume of the substrate that can potentially be filled by air or
water. Therefore a good propagation substrate should have a total porosity of 65-70%. Reference
should also be made to free porosity (macroporosity), defined as the percentage by volume of a
substrate corresponding to the empty spaces after gravitational water drainage. This type of porosity
should range between 15 and 30%.
Water retention capacity
The percentage volume of water remaining within the substrate at full gravitational water drainage
represents the water retention capacity. It is related to the total volume of pores so small (≤ 8-10
µm) that they exceed the force of gravity, and corresponds to the microporosity of the substrate. Its
value should be between 25 and 35%, but it can reach higher levels especially in peat. The smaller
the size of the micropores, the greater the amount of water retained. The water retention capacity
influences the frequency of irrigation.
Cation exchange capacity (CSC)
Indicates the ability of a substrate to retain positively charged ions. Peat, coconut fibre, vermiculite
and bark have a negative electrical charge and therefore retain cations that can be released to the
solution circulating inside the substrate and then absorbed by the plant's root system. The greater
the exchange capacity, the greater the number of nutrients in the form of cations that the substrate
can retain. Capacity expressed in thousand-equivalents per 100 g of substrate (meq/100g). It is very
important because most of the nutrients are in the form of cations (NH4, K, Ca, Mg, Zi, Cu, Mn,
Fe).
Ph
It is the degree of measurement that expresses the degree of acidity or alkalinity of a solution. It is
defined as the measurement of the concentration of hydrogen ions in the nutrient solution of the
substrate. It's expressed on a scale from 1 to 14. The pH 7 value represents neutrality; a value above
7 indicates a basic pH and a value below 7 an acid pH. It is well known that succulent plants usually
like a neutral (7) or slightly acidic (6-6,5) pH, except for the epiphytes, which want it a little more
acid, and others, on the contrary, which like it more alkaline.
Six simple optical comparison colorimetric kits can be used for measurement. Pour a tablespoon of
soil into 30 ml of demineralised water, mix and leave to rest for 24 hours, then filter through a
funnel in the hole of which bibular paper or a sock has been inserted. 5 ml of liquid is taken and
poured into the graduated tube included in the test and colorimetric comparisons are made.
Otherwise you can buy a professional piaccametro that provides more accurate and easier to make
measurements.
Fertilizers
They are able to supply mineral elements to the ground, you can find natural (organic) and chemical
elements in various titles and forms: liquids, powder, grains, etc.. In a good substrate of propagation
and cultivation must be present: nitrogen, phosphorus, potassium, calcium, sulfur, magnesium, iron
essential for the life of plants. During the germination phases, the seeds already contain sufficient
nutrient reserves to fulfil the first phases, so it is not necessary to provide nutrients. Fertilizers are
required as soon as the cotyledons are visible. It is usually possible to use a ternary fertiliser (N-P-
K) (20-10-20) at a dose of 50 mg/L. This dose can be increased up to 100-150 mg/L in the
following steps. The measurement of the electrical conductivity of the substrate allows you to
monitor the salinity of the solution circulating at the root level and check for any imbalances. The
values must be between 0,5 and 1,2 dS/m at sowing and germination and between 0,9 and 2,5 dS/m
at the stage when the seedling is well rooted.
Nitrogen is a growth regulator necessary for protein synthesis and the formation of living matter. It
is present in organic matter and humus, and is transported by phloem and xylem. It provides for the
construction of the structure of plant tissues together with the hydrogen and oxygen of water and
photosynthetic carbon. Some microorganisms are able to transform organic nitrogen into
ammoniacal and therefore nitric, which is the form in which plants can most easily assimilate it (80-
90%). No plant is able to fix atmospheric nitrogen without entering into symbiosis with bacteria of
the genus Frankia. Fleshy plants require little nitrogen, otherwise they will become susceptible to
disease.
Phosphorus is the constituent of nucleic acids (Dna-Rna), and adenosine triphosphate (ATP), it is
present in chromosomes and its organic compounds are fundamental in energy processes. It
stimulates apical and radical meristems, contributes to the maintenance of good health, strengthens
the defences against diseases and adversities, promotes flowering and seed formation, transforms
raw sap into processed. Bone meal and guano are, among the natural fertilizers, those with the
highest content of phosphorus.
Potassium is fundamental in the osmotic process of the cells, present in the cytoplasm and in the
vacuoles, it determines the internal hydraulic pressure, strengthens the plants, forms the sugar
reserve, gives colour to the flowers, regulates the transpiration. A deficiency in it makes the plant
look withered. Potassium sulphate with a titre of 50-52 is used.
Sulphur and calcium are generally sufficient in field soil, but not always in prepared soils. The first
is sulphur amino acids, and is responsible for protein synthesis; the second is a component of cell
membranes and pectins, activates enzymes, neutralizes organic acids, slows down tissue aging,
strengthens the plant against parasite attacks, supervises water turnover, lymph transport and root
development.
Magnesium is a component of chlorophyll, it facilitates the transfer of phosphorus, it is an activator
of biochemical reactions, it enters into the synthesis of starch and sugars.
Iron is used for the development of chloroplasts for the synthesis of chlorophyll, regulates
photosynthesis and cell respiration, and enters into the constitution of various enzymes. The intake
takes place in chelated form (EDTA, DTPA, EDDHA). A lack of this causes ferric chlorosis, which
gives the plant a yellowish colour.
Among the trace elements that must be present, but in minimal quantities:
- boron: sugar transport and meristematic development
- manganese: photosynthesis and enzymatic activation
- copper: enzymatic activation and protein synthesis
- zinc: enzymatic activation, synthesis of proteins and hormones
- chlorine: photosynthesis
Microelements are fundamental to cell enzyme systems, act as cofactors and can be absorbed by the
leaves. The nutrient solution is mainly taken by means of the roots by osmosis and by active
absorption. It does not fertilize during the rest of the plant, nor after transplanting. The ratio of the
main elements nitrogen, phosphorus and potassium should be 1-2-4 or 1-3-5, i.e. little nitrogen,
much phosphorus, much potassium. For fertilising you can use the method of watering or mixed
with the soil. (Cecarini, 2011)
Substrate disinfection
The practice of substrate disinfection is essential for the use of old soil, or for the use of delicate
sowings. The aim is to eliminate any unwanted seeds, cryptogamic spores, eggs and insect larvae.
Some executable methodologies are as follows:
- water the substrate well with boiling water
- use the oven at 100°C for at least 30 minutes, or the microwave oven at full power for the
same time
- use 40% formaldehyde to be diluted in water at the time of use in a ratio of 1:50 (Cecarini,
2011).
Components used in substrates (organic materials) (Iapichino, 2012)
Peat
It is extracted from deposits of partially decomposed debris and accumulated in cold, marshy and
humid environments in Canada, northern Europe, Russia. The plant species that lead to the
formation of the peat belong to the genera Sphagnum, Caryx, Fragmites and Hypnum. The substrate
is marketed in plastic bales of various volumes. One problem with the use of this substrate is
dehydration. Mixtures with a high proportion of peat (more than 60-70%) shrink when their water
content is too low. The excessive use of peat, being a non-renewable material, has caused a great
deal of environmental criticism in recent years, especially in Europe, and consequently a trend
towards the search for alternative substrates.
Coconut fibre
It is a vegetable material obtained from the shelling of coconuts and which has characteristics
similar to those of sphagnum peat. During processing, smaller fibre fractions are removed,
compacted for 2-3 years and then dehydrated. Coconut fibre absorbs water much more easily than
sphagnum peat. It has excellent water retention, ventilation and good cation exchange capacity (40-
60 meq/100g). It has good stability over time, as it slowly decomposes and excellent resistance to
compaction.
Bark
By-product of woodworking. Pine bark and pine compost have long been used for pot crops and
their use has been extended to the preparation of propagation substrates. The most used conifers are
Picea abies, Pinus pinaster, Pinus sylvestris, Pinus nigra maritima, Sequioa, Cedrus, Abies. The
bark is an excellent substitute for peat, but has a lower capacity for water retention.
Compost
It is the result of the decomposition and humification of various organic materials by various
microorganisms, mainly bacteria, fungi and actinomycetes. For the composting process to take
place in the best possible way, the moisture content inside the mass must be 50-65% and
temperatures of 45-55°C must be reached.
Components used in substrates (inorganic materials) (Iapichino, 2012)
Vermiculite
Hydrated magnesium, aluminium and iron silicate which, when subjected to heat treatment at
760°C, expands to form a porous structure in parallel sheets (total porosity 94-96%). It retains up to
five times its weight of water thanks to its thin-flap structure, but has little resistance to
compression. Vermiculite is characterized by high buffering power and high values of cation
exchange capacity.
Perlite
It is an aluminium silicate of volcanic origin. The water in the granules evaporates to form closed-
cell aggregates. White, sterile material, marketed in particles of various particle sizes, with an
irregular shape. It retains water only on the surface and in the spaces between the aggregates and
has a water retention capacity of 15-35%. It has a low cation exchange capacity and its prolonged
use causes a change in colour from white to yellow.
Sand
It is the heaviest of all the substrates (1400/1600 Kg/m3) and comes from the decomposition of
various types of rocks. Silica sand with particles between 0.02 and 2.0 mm in size is generally used
for plant propagation. It contains few or no nutrients; the one of marine origin has a high content of
sodium chloride so it must be washed.
Polystyrene
It is sometimes used as a substitute for perlite as the granules increase the porosity and drainage of a
substrate. Light material that does not deteriorate over time at neutral pH.
Pumice
Aluminium silicate of volcanic origin, pumice improves the drainage and ventilation of substrates.
It is marketed in various particle sizes and has a tendency to deteriorate due to the disintegration of
the particles. Contains small amounts of sodium, potassium, calcium, magnesium, iron and has a
neutral pH.
Expanded clay
It is obtained by treating the clay at 700°C. It increases the drainage and aeration of the substrate
and is used with organic materials in a percentage of 10-35% for the preparation of mixtures for
pots.
Rock wool
It is obtained through the fusion at 1500-2000°C of aluminium, calcium, magnesium and carbon
coke silicates. Produced in various shapes and sizes such as blocks, blocks and cubes, it is able to
absorb considerable quantities of water while maintaining good porosity and aeration of the root
system.
Zeolitites and zeolites
Zeolites are a family of minerals consisting of 52 species, which can be chemically defined as
"alumino-silicate hydrates of alkaline and/or alkaline-earthy elements (essentially, Na, K, Ca)" and,
structurally, belonging to the roof-silicates such as silica minerals, feldspars and feldspatoids.
By virtue of their crystallochemistry, zeolites have the following chemical-physical
characteristics:
high and selective cation exchange capacity (CSC) for low ion potential cations (NH4, K,
Pb, Ba, Cs, Sr)
reversible dewatering
selective molecular adsorption
catalytic behavior.
In addition to beautiful macro- and microscopic crystals of "hydrothermal" genesis formed within
fractures and cavities of effusive magmatic rocks (especially basalts) of which they form a
subordinate part (5 -10%), zeolites occur in submicroscopic crystals (1-20 m) evenly distributed
within pyroclastic rocks (tuffs, ignimbrites) of which they are diagenized (20- 40%) or
preponderant (50-70%).
In substitution of the generic and improper terms ("natural zeolites", "sedimentary zeolites",
"rocks rich in zeolite", "tuffs rich in zeolite") normally used in literature, the name "zeolite" has
been introduced in order to define in a scientifically correct way the diagenised pyroclastic rocks
with a prevalent (> 50%) zeolite content and subordinate amounts of other silicate phases (quartz,
cristobalite, feldspar, plagioclase, pyroxen, mica) and volcanic glass. The most common zeolithic
species in the "zeolites" are: clinoptilolite (Figure 1) present in variable quantities (40-60%) in
diagenized "acid" tuffs spread in many European countries (Slovenia, Czechoslovakia, Hungary,
Romania, Bulgaria, Greece) and extra-European countries (Turkey, Iran, Russia, USA, Cuba,
Japan, China, Australia); chabasite (Figure 2) and phillipsite (Figure 3) present in variable
quantities (30-70%) especially in Italian alkaline-potassium "basic" ignimbrites (Figure 4).
Figure 3.- SEM photo of prismatic phillipsite crystals from the "Yellow Neapolitan Tuff".
The "zeolites", due to their content in zeolite, possess:
a) high (1.4 -2.1 meq/g) and selective cation exchange capacity
(b) reversible dehydration
(c) structural cryptoporosity
and, by their lithological nature (micro and macro tissue porosity, lithoid consistency), present:
(a) water retention
(b) mechanical strength
(c) permeability
(d) low density
The zeolithic properties (cation exchange capacity, reversible dehydration, structural porosity)
depend on the type and concentration (%) of zeolite present in the rock
Figure 2.- SEM photo of pseudocubic chabasite crystals
of the "Red Tuff with black pumices" (Latium-Tuscany).
Figure 1.- SEM photo of clinoptilolite lamellar
crystals of Greek zeolitis.
The other properties (water retention, mechanical resistance, permeability, density) depend on the
nature (tuff, tufite, ignimbrite) and the diagenetic process (hydrological system "open", "closed",
"geoautoclave") suffered by the volcanic rock.
Since chabasite and phillipsite are zeolithic species with CSC of 3.3 - 3.4 meq/g and are found in
ignimbrites with micro and macroporous texture while clinoptilolite is a zeolithic species with CSC
of 2.2 - 2.3 meq/g and is found in compact tuffs, the chabasite and phillipsite zeolites widespread in
Italy show higher CSC and water retention values and lower density values than those of the
clinoptilolite zeolites widespread abroad.
Use of zeolites in Agriculture and Floriculture- In agronomic field s.l., zeolites, classifiable as
such only if the zeolite content of the rock to which they belong is higher than 50% on the basis of
X-ray analysis using only the Rietveld-RIR methodology (attached to the Decree of the Ministry of
Agriculture, Food and Forestry of 27 January 2014 n. 1377 supplement n.12).), were included
among the soil conditioners by Decree of the Ministry of Agricultural, Food and Forestry Policies
of 3 March 2015 and in Organic Farming by Decree of 17 January 2017 published Official Gazette
of the Italian Republic of 3 March 2017 General Series n.52.
The use of zeolites both in the natural state and enriched in NH4 (through cation exchange or
"exhausted" product of wastewater purification processes) as a corrective of soils and substrates
involves: increase in water retention, cation exchange capacity (CSC), permeability and degree
of aeration of soils, solubilization of tricalcium phosphates, neutralization of excess acidity and
reduction of the assimilation by crops of harmful elements (Pb, Cd) and radiogenic (Cs, Sr), weak
but significant reduction in the intensity of the temperature range of the soil, significant reduction
in the salinity of water for irrigation use
The optimal quantity of zeolites to be applied as a correction varies with the type of soil: 1 - 2
Kg/m2 in soils with a predominantly sandy component; 2 - 4 Kg/m2 in soils with a predominantly
clayey-loamy component. It can be used in soils with the addition of 20% in volume of substrate,
this ensures better supply of water and nutrients, reduction of water and temperature stress,
reduction of compaction and improvement of aeration of the substrate, promotes the development of
bacteria symbionts (Passaglia and Prisa, 2018; Prisa and Burchi 2015a,b; Prisa 2017a,b; Prisa,
2018; Prisa and Castronuovo, 2018).
Substrates for cactus cultivation
General formula
- 4 parts of universal soil
- 1 part humus
- 3 parts of pumice
- 2 parts chabasite zeolite (grain size 3-6 mm)
Alternative formula
- 2 parts of universal soil
- 2 parts humus
- 2 parts of pumice
- 2 parts of lapillus
- 2 parts chabasite zeolite (grain size 3-6 mm)
You can add 0.5% spirulina, 0.5% bone meal, 0.5% pelleted manure or bat guano
Cactus and succulent experiments with zeolite-based substrates
Experimentation on delosperma
Addition to the substrate of cultivation of 20% by volume of zeolite to 3-6 mm chabasite (chabasite
thesis)
Experimentation on sedum
Addition to the cultivation substrate of 10% by volume of zeolite to 3-6 mm chabasite (chabasite
thesis)
Cactus seeding experiment
Addition to the substrate of cultivation of a 10% in volume of zeolite to chabasite 0-3 mm
(chabasite thesis)
Experimentation with aloe vera and arborescens
Addition to the substrate of cultivation of a 10-20% by volume of zeolite to chabasite 3-6 mm
(thesis 1 chabasite 10%, thesis 2 chabasite 20%)
References
E. Passaglia, D.Prisa (2018). Contributo delle zeolititi nella mitigazione delle problematiche
ambientali conseguenti alle vigenti pratiche agricole. Edizioni lulù. ISBN: 9780244661120. 160p
D.Prisa, G.Burchi. (2015a). La forza della chabasite. Il floricultore 10-11:40-44
D.Prisa, G.Burchi. (2015b). Piante più forti con la chabasite. Il floricultore 10:2-5
D. Prisa, (2017a). Microrganismi EM e zeolite a chabasite per la coltivazione di ibridi di
Echinopsis. Il floricultore 2017
D.Prisa (2017b).Microrganismi EM e zeolititi aiutano la coltivazione di Euphorbia e Crassula. Il
floricultore Settembre 2017
D.Prisa (2018). La coltivazione di Aloe Vera e A. Arborescens con metodi sostenibili. Il
floricultore Aprile 4:41-45
D.Prisa, G.Castronuovo. (2018). Succulente, cactacee e soluzioni innovative per giardini salva
acqua. Il floricultore 2:39-43
G. Iapichino (2012). La propagazione delle piante. Edagricole. ISBN: 978-88-506-5354-6
M. Cecarini (2011). Piante Grasse: Le cactacee. Guida pratica completa per coltivare, riconoscere,
moltiplicare, difendere, curare le piante grasse. ISBN: 978-88-97955-09-2