American Journal of Plant Sciences, 2019, 10, 925-946
ISSN Online: 2158-2750
ISSN Print: 2158-2742
10.4236/ajps.2019.106067 Jun. 18, 2019 925 American Journal of Plant Sciences
Cannabis Indoor Growing Conditions,
Management Practices, and Post-Harvest
Treatment: A Review
Dan Jin1,2*, Shengxi Jin2, Jie Chen1,3
1Biomedical Engineering Department, University of Alberta, Edmonton, Canada
2Labs-Mart Inc., Edmonton, Canada
3Electrical and Computer Engineering Department, University of Alberta, Edmonton, Canada
Cannabis has attracted a new wave of research attention as an herbal medi-
cine. To deliver compliant, uniform, and safe cannabis medicine, growers
should optimize growing environments on a site-specific basis.
that environmental factors
are interconnected, changes in a factor prompts
adjustment of other factors. This paper reviews existing work that considers
indoor growing conditions (light, temperature, CO2
growing media, and nutrient supply), management practices (irrigation, fer-
tilization, pruning & training, and harvest timing), and post-harvest treat-
ment (drying and storage) for cannabis indoor production.
Cannabis, Environmental Factors, Growing Conditions, Post-Harvest
Treatment, Indoor Cultivation, Agrology, Agricultural Science
Cannabis is an annual, non-obligate dioecious plant that is used as a complex
botanical medicine containing more than 100 identified cannabinoids . Can-
nabinoids belong to the chemical classification of terpenophenolics, which are
widespread in plants. The most important and frequently detected cannabinoids
are tetrahydrocannabinolic acid (THCA), ∆9-tetrahydrocannabinol (∆9-THC),
∆8-tetrahydrocannabinol (∆8-THC), cannabidiolic acid (CBDA), cannabidiol
(CBD), cannabigerolic acid (CBGA), cannabigerol (CBG), cannabinolic acid
(CBNA), cannabinol (CBN), cannabichromenic acid (CBCA), cannabichromene
How to cite this paper:
Jin, D., Jin, S.X.
Chen, J. (2019) Cannabis Indoor Grow-
ing Conditions, Management Practices, and
-Harvest Treatment: A Review.
ican Journal of Plant Sciences
March 14, 2019
June 15, 2019
June 18, 2019
Copyright © 201
9 by author(s) and
Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
License (CC BY
D. Jin et al.
10.4236/ajps.2019.106067 926 American Journal of Plant Sciences
(CBC), cannabicyclolic acid (CBLA), and cannabicyclol (CBL) . Cannabis can
be classified either as drug-type plants that have high THC concentrations or
as fibre-type plants that are referred to as hemp. Biosynthetic pathways for
cannabinoids have been research hotspots since their discovery. The most
widely-accepted biosynthetic pathway was proposed by Taura   and Mo-
rimoto , in which CBGA is the direct precursor of THCA, CBCA and CBDA,
where CBGA is biosynthesised by geranyl diphosphate (GPP) and olivetolic acid
 . It is crucial to understand how cannabinoids are related with each other
when studying cannabis, considering that degradation (including decarboxyla-
tion, isomerization, irradiation, and oxidation) can affect the chemical compo-
nents through improper operations or during long-term storage with unsuitable
conditions, which may severely alter experimental results. Biosynthetic pathways
for the production of cannabinoids, including degradation products , are
demonstrated in Figure 1. Current research tends to focus on THC, which is
psychoactive. However, non-psychoactive cannabinoids such as CBD, CBG, and
CBC also have broad therapeutic potential . Apart from cannabinoids, terpe-
noids, which are responsible for cannabis’s distinctive odour, are receiving in-
creasing attention for their suggested synergistic interactions with cannabinoids
 . Large amounts of active ingredients endow cannabis with a wide range
Figure 1. Relationships between the major cannabinoids found in cannabis .
D. Jin et al.
10.4236/ajps.2019.106067 927 American Journal of Plant Sciences
of potential therapeutic uses, including the treatment of nausea or vomiting as-
sociated with chemotherapy, anorexia associated with AIDS-related weight loss,
spasticity and neuropathic pain associated with multiple sclerosis and intractable
cancer pain .
Since the turn of the 21st century, cannabis for medical purposes has trended
globally and became particularly well established in North America. To achieve a
consistent profile of effective components in cannabis as an herbal medicine,
significant work has been carried out to investigate the mechanism of cannabi-
noid production. According to recent studies, genetics, growing conditions,
manner of drying and storage, and methods of processing and extraction may
affect the concentration and profile of pharmaceutically active ingredients de-
rived from cannabis . Within a specific cultivar, the ratio of THC and CBD
remains consistent in both male and female plants   as well as in leaves
and flowers throughout vegetative growth and flowering stages   .
However, the density of floral bracts and bracteoles that carry glandular
trichomes, where cannabinoids and terpenes are biosynthesized and stored, is
higher in female plants than in males . Concentration also varies in different
plant parts, decreasing in the order of inflorescences, leaves, stem, seeds, and
roots  . The ratio of THC to CBD is a qualitative trait and the total yield
of THC plus CBD is a quantitative trait . Based on this concept, another
study calculated cannabinoid yield in a fixed cultivation area as the product of
four components: 1) total dry, above-ground biomass; 2) inflorescence leaves
and bracts as a proportion of total plant biomass; 3) total cannabinoids in the in-
florescence leaves and bract fraction; and 4) “purity”, the proportion of one
cannabinoid out of total cannabinoids . The last component “purity” is a
qualitative trait controlled by a simple genetic mechanism that is minimally af-
fected by environmental factors, while the first three components are quantita-
tive traits controlled by different polygenic mechanisms that are heavily affected
by the environment .
Cannabinoid yield in a fixed area
One cannabinoid Total cannabinoid
Total cannabinoid Yield of inflorescence
Yield of inflorescence
Yield oftotal plant biomass
Yield of total plant biomassin a fixed area
In the modern cannabis industry, strains with high THC potency are predo-
minantly propagated in controlled environment systems, such as growth cham-
bers or greenhouses . The process starts with seeds or cuttings and uses light
schedules to trigger and control the duration of the vegetative and flowering
stages  (Figure 2). Environmental factors, including growing conditions,
horticultural management practices, and post-harvest processing (curing, ex-
traction, etc.), combine with genetics to contribute to the variation in medicinal
profiles of the final products. The Dutch government has issued a quality
D. Jin et al.
10.4236/ajps.2019.106067 928 American Journal of Plant Sciences
Figure 2. Environmental factors throughout the growing process impact cannabis yield
assurance system for standardizing cultivation, harvesting and processing of
cannabis, including strain, growing medium, light cycle, light intensity, colour
temperature of the lighting, humidity, temperature, ventilation, plant age at
harvest, time of day for harvesting, drying facility humidity and temperature,
drying facility ventilation rates, and drying time . The American Herbal
Pharmacopoeia (AHP) has also issued standards of identification, analysis, and
quality control of cannabis based on peer-reviewed literature . This article
provides a comprehensive review of the current scientific knowledge on horti-
cultural practices for indoor medical cannabis production. Harvest yield and
consistency depends on environmental factors, which have interdependencies
and interactions. Changes in one factor may have profound effects on how the
plants respond to others . Therefore, an integrated approach to analyzing
growing practices is required.
1.1. Growing Conditions
Light, both the quality (spectrum) and quantity (intensity), plays an important
role in cannabis cultivation in controlled environmental systems, where plants
capture energy from light and assimilate CO2 and water into dry matter through
Plants utilize light in the visible spectrum between 400 nm
and 700 nm, which is typically referred to as photosynthetically active radiation
(PAR). Blue light tends to decreases internode length while a low red/far-red ra-
tio promotes stalk elongation . Ultraviolet A light (UVA, 315 - 400 nm)
helps reverse damage to DNA caused by Ultraviolet B light (UVB, 280 - 315 nm)
 . UVB is reported to increase THC levels in plants; THC is thought to
be a UVB photo-protectant   . Lydon (1987) found a significant lin-
ear relationship between THC content (mg/g d.w.) in floral tissue and UVB dose
in drug-type plants, whereas other characteristics such as physiology, leaf mor-
D. Jin et al.
10.4236/ajps.2019.106067 929 American Journal of Plant Sciences
phology, and content of other cannabinoids (such as CBD) in drug- and fi-
bre-type plants were unaffected . THC content in floral tissue increased from
25% to 32% when the daily effective UVB dose was raised from 0 kJ/m2 to 13.4
kJ/m2. However, this paper only reviews two chemotypes (one each of drug- and
fiber-types) and three levels of daily effective UVB doses (0, 6.7, and 13.4 kJ∙m−2
UVB), thus more data are required to draw firm conclusions.
For indoor cultivation, commonly used lamps include fluorescent lamps (FL),
metal halide lamps (MH), and high-pressure sodium lamps (HPS). The ability to
transform electrical energy to PAR varies between lamps, as does the spectra
emitted. For example, the type of phosphor used to coat the surface of CFLs de-
termines the spectral output. Whereas MH lamps emit insufficient red light to
produce heavy flowers, HPS lamps are heavily concentrated in the yellow, or-
ange, and red spectra with a small amount of blue. A combination of several
lamps may be utilized to cover desired wavelengths.
More recently, light emitting diode (LED) fixtures with adjustable spectra
have been developed. One study compared the effects of three light spectra, in-
cluding one HPS and two types of LEDs (AP673L and NS1), on the morphology
and cannabinoid content of cannabis clones . The spectrum produced by
HPS was 96% PAR and was heavily concentrated with green/yellow (68%) and
orange/red (21%) and less concentrated in violet/blue (8%). In comparison, the
AP673L spectrum was 93% PAR and more concentrated with orange/red (59%)
than green/yellow (20%) and produces more violet/blue light (14%). The NS1
spectrum was 94% PAR and spread between green/yellow (37%), orange/red
(33%), and violet/blue light (24%). The percentage of UVA was 1% in HPS, 0%
in AP673L, and 2% in NS1. At maturity, plants grown under the two LEDs were
shorter and more compact than those grown under HPS due to increased red
and blue emission. HPS resulted in higher flower yields (26.6 g per plant) com-
pared to LED treatments (23.1 g and 22 g for AP673L and NS1, respectively).
These results are comparable to a study by Vanhove
, (2011), where flower
yield per plant was 20.1 g under similar lighting conditions . The author did
not volunteer any explanation for the decreased yield of LEDs—results from
other studies imply that the high thermal efficiency of LEDs decreased the over-
all heat load, thereby reducing temperature and decreasing evapotranspiration
rate, net photosynthesis (PN), CO2 assimilation, and, ultimately, yield . Al-
though the dry flower yield (g/plant) is higher with HPS, it also resulted in the
lowest THC mass proportions (9.5%) while NS1 LED resulted in the highest
(15.4%); this may indicate a positive effect from blue and UV-A light, which was
more prominent with NS1 than the other lamps. One alternative explanation is
that the low red to far-red light ratio in HPS lamps induced shade avoidance
syndrome in plants, reducing phytochemical biosynthesis. Interestingly, despite
inducing different morphologies and cannabinoid concentrations, the different
lamp treatments did not result in significant differences in total cannabinoid
yield (3.2 g/plant for HPS and 4.3 g/plant for NS1, p > 0.05). LED technology
enables the manipulation and optimization of light spectra and could be a useful
D. Jin et al.
10.4236/ajps.2019.106067 930 American Journal of Plant Sciences
tool for modulating cannabinoid profile and improving yields of specific com-
In a recent study, subcanopy lighting (SCL) utilizing LED lights improved
cannabis flower quality, consistency, and yield . In this study, plants were
not exposed to supplemental SCL or exposed to one of the two kinds of supple-
mental SCL spectra: red/blue (Red-Blue) and red-green-blue (RGB), positioned
15 cm to the side of the plant stem and raised 2 cm off the soil surface during the
flowering stage. Both Red-Blue and RGC SCL increased the yield of dry flowers
compared to the control due to increased amount of light being delivered to
plants. Both Red-Blue and RGCSCL increased yield and concentration of total
THC in flowers from the lower plant canopy compared to the control treatment.
Red-Blue produced a more homogenous cannabinoid and terpenoid profile
throughout the canopy (between the upper and lower canopies).
There is a close relationship between yield and photosynthetic
rate . Chandra
carried out a series of experiments to study the effects of
light intensity, CO2 concentration, and temperature on individual leaves 
 . The PN and water use efficiency (WUE) of a high potency Mexican
drug-type variety increased to a point, with increasing PPFD (0, 500, 1000, 1500,
and 2000 μmol/m2/s) at 20˚C and 25˚C . At 30˚C, both PN and WUE in-
creased up to 1500 μmol/m2/s PPFD and decreased at higher light intensities. At
higher temperatures (35˚C and 40˚C), higher PPFD (2000 μmol/m2/s) showed
an adverse effect on PN and WUE . The rates of transpiration (E) were posi-
tively correlated with increasing PPFD and temperature (2000 μmol/m2/s and
40˚C), but leaf stomatal conductance (gs) increased with PPFD up to 30˚C only
. The maximum of PN (PNmax) for this variety was observed at 30˚C with a
PPFD of 1500 μmol/m2/s . In another study, all four drug varieties from
Mexico and Switzerland show increasing PN with increasing light intensity with a
range of (0, 400, 800, 1200, 1600, and 2000 μmol/m2/s) PPFD at 25˚C ± 3˚C .
Although the trend of PN increasing with PPFD is similar for different varieties,
the magnitude of increase and PNmax varied considerably with the four varieties
studied, with PNmax higher in three Switzerland varieties than one Mexican vari-
ety . However, the relationship between higher photosynthesis rate and
higher cannabinoid yields has not been conclusively demonstrated . Potter
(2009) compared leaf tissue collected from a rare variegated cultivar, which had
leaves coloured green and yellow on opposite sides of the midrib, and found that
photosynthetic ability has minimal effect on the cannabinoid synthesis on local
glandular trichomes . The THC content (w/w%) of yellow leaf tissue was
higher than green leaf tissue on the symmetrically opposite side of the same leaf.
To investigate the influence of light intensity on cannabinoids and terpene pro-
duction, further research is required under controlled environments over a longer
term and on whole plants.
When CO2, nutrients, water, and temperature are not limiting factors, dry
matter production is proportional to the amount of light intercepted by a crop
canopy . Because area is a limiting factor for indoor production, the amount
D. Jin et al.
10.4236/ajps.2019.106067 931 American Journal of Plant Sciences
of light received per plant is heavily influenced by plant density. With a fixed
density, the amount of light received per plant and per square meter is propor-
tional to light intensity at canopy level such that higher light intensity increases
yield per plant and per square meter before light saturation occurs. Potter em-
phasised the close-to-linear correlation between the irradiance level at the com-
mencement of flowering and the subsequent final yield . At the initiation of
flowing, the plants maximize light energy usage by developing dense foliar cano-
pies. As a result, increasing PPFD from 78 μmol/m2/s (converted from 17 W/m2
of mercury vapour lamps by an conversion factor of 4.59 ) to 274 µmol/m2/s
(converted from 55 W/m2 of HPS lamps by a conversion factor of 4.98 ) at
plant canopy resulted in a significant increase (p < 0.01) in yield per square me-
ter. A follow-up study measured yield and THC concentrations under PPFD of
400, 600, and 900 μmol/m2/s (converted from 80, 120, and 180 W/m2of HPS
lamps by a conversion factor of 4.98 ) at the canopy and did not find an in-
crease in concentration at brighter conditions. However, the overall floral THC
yield (g/m2) increased because plants in brighter conditions yielded more floral
material . In contrast, increasing irradiance did not significantly affect THC
concentration or yield in leaf tissue; high light intensity at high temperatures
may adversely affect PN. Additionally, high light intensity is costly. The same
study also investigated mean inflorescence yield per unit of electrical power—
results ranged from 0.9, 1.2, to 1.6 g/W, with the highest yield efficiencies occur-
ring at the lowest power consumption levels (600 W/m2, 400 W/m2, 270 W/m2).
The result was explained by a decreasing tendency for plants to convert light en-
ergy into biomass with increasing light saturation at high irradiance levels. This
can be used as a reference for licensed producers and individual growers to bal-
ance financial input/output when setting up a growing area. A comparison of
effects of lighting intensity on the mean yields of dry cannabis flower under dif-
ferent electrical power consumption (400 W/m2, 510 W/m2, 600 W/m2) in four
published European studies suggested that the mean yield of dry cannabis flower
is approximately 1 g/W, while electrical energy consumption per gram of yield
averaged approximately 1 kWh/g from planting to harvest .
With the same light output and room size, increasing plant density beyond a
certain point decreases light interception per plant, resulting in decreased yield
per plant, but the total room yield remains constant. One study investigated two
light intensities (one 600 W HPS lamp per square metervs. one 400 W HPS lamp
per square meter), two plant densities (16 plants/m2 density vs. 20 plants/m2),
and four varieties in a total of sixteen scenarios. It concluded that all three fac-
tors significantly affect yield per plant; however, plant density had no effect on
yield per square meter . This indicates that light interception is the limiting
factor for total indoor yield. Specifically, yield per plant increased with light
wattage, decreased with density, and was significantly different between culti-
vars. Similar observations were made on yield per area, except that yield per area
is independent of plant density. Based on these results, light intensity and plant
density are considered as independent additive factors. This topic is of interest to
D. Jin et al.
10.4236/ajps.2019.106067 932 American Journal of Plant Sciences
industrial growers, and studies are required to determine the optimized combi-
nation of light intensity with plant population to fully utilize light and space re-
sources to maximize yield and profitability. However, there must exist upper and
lower thresholds at which plant density will affect yield per area, either in ex-
treme overcrowding or sparseness situations. Such thresholds have not been in-
Cannabis is a “short-day” plant that naturally flowers in late
summer , where it needs uninterrupted and sufficiently long nights to initi-
ate flowering. This process is regulated by a class of photoreceptors in the plants
called phytochromes . Phytochromes exist as two photoreversible forms: the
red light absorbing form (Pr) and the far-red light absorbing form (Pfr), the latter
of which inhibits flowering . In the dark, the active form Pfr slowly reverses
back to the state form Pr, but the fewest photons of a flash red light with a peak
near 667 nm, which is found in both daylight and lamp light, can convert the Pr
to Pfr, subsequently, inhibits flowering  . For indoor cultivation, a regi-
men of 18 hours or 24 hours of continuous light has been used for vegetative
growth. A schedule of 12 hours of light and 12 hours of darkness is considered a
short day length, and has been widely utilized to initiate flowering—the first
flowers are visible one week after the light schedule change . The critical day
time length is related closely with a variety’s geographical origin, especially those
originating far from the equator . Because day time in all latitudes in the
North Hemisphere is longer than 12 hours at summer solstice, 12 hours of
darkness will initiate flowering for most varieties. Eleven hours of darkness ini-
tiated flowering in tropical varieties, possibly due to plant age instead of light
The effect of light regimen on plant development and cannabinoids profile
were studied by Potter by subjecting dozens of cannabis varieties (clone lines) to
either 11, 12 or 13 hours of light (short day length) after three weeks of vegeta-
tive growth under continuous light for 24 hours . The first part (comparison
of 12 and 13 hour of light) of the study was carried out in glasshouses while the
second part (comparison of 11 and 12 hours of light) was carried out in an in-
door environment. The results are summarized in Table 1. The yield of total
floral and foliage material of plants was referred to as Botanical Raw Material
(BRM) yield (g/m2). The mean BRM yield (g/m2) and the cannabinoid yield
(g/m2) of plants was significantly higher when grown under 12 hours of light
compared to 11 hours. There was no benefit in increasing from 12 to 13 hours of
light, but there were large decreases in yield in decreasing from 12 to 11 hours of
light. Therefore, a 12-hour light regime is the most energy-efficient and eco-
nomical . It is notable that although there is no significant difference in
mean values of all clone lines of some effects investigated, for example, the mean
height, the total floral and foliage material (g/m2), and the cannabinoid yield
(g/m2), these effects varied with individual clone lines (strains). Each strain re-
quires unique growing conditions and harvest timings that should be investi-
gated and optimized within its specified growing environment.
D. Jin et al.
10.4236/ajps.2019.106067 933 American Journal of Plant Sciences
Table 1. The effect of light regimen on plant development and cannabinoids profile.
Glasshouse (10 clone lines)
Indoor/Artificial Light (12 clone lines)
Eight weeks in short light
Ten weeks in short light Eight weeks in short light Ten weeks in short light
12 hours 13 hours 12 hours 13 hours 11 hours 12 hours 11 hours 12 hours
Proportion of senesced stigmas
Higher Lower Higher Lower NSD
NSD NSD NSD
Mean height of all clone lines
NSD NSD Shorter Taller NSD NSD NSD NSD
Mean yield of BRM (g/m2)
NSD NSD NSD NSD Lower Higher Lower Higher
Cannabinoid yield (g/m2)
NSD NSD NSD NSD - - Lower Higher
Proportional CBG content
(CBG as % of CBG + THC)
Lower Higher Lower Higher NSD NSD NSD NSD
Proportional THCV content
(THCV as % of THCV + THC)
Higher Lower Higher Lower - - - -
No significant difference (p > 0.05).
Light cycle in the vegetative stage.
Under a continuous light regimen of 24 or
18 hours of light per day, cannabis plants remain vegetative. Vegetative growth
shifts to reproductive growth after a two week exposure to 12 continuous hours
of light per day . Cuttings from a THC dominant variety were grown in-
doors by Bedrocan VB (Netherlands) under 18 h of light for 37 days of vegeta-
tive stage and 12 h of light for 40 days of flowering stage . One batch was
grown under standard conditions and other three batches were grown with one
less week of vegetative growth plus one extra week of flowering, one extra week
of vegetative growth, one extra week of vegetative growth and one extra week of
flowering, respectively. Differences were observed in certain compounds com-
pared with the standard batch. The conclusion was that alterations in growth cy-
cle time appear to cause more differences in chemical profile than growing cut-
tings in different batches .
Light cycle in the flowering stage
. A recommended growth period for 200 in-
door high-THC cannabis varieties from 20 producers in Europe is between seven
to nine weeks in short day length, with a mean recommended duration of 57
days . In order to study the effect of duration of flowering period on can-
nabinoid yield, 25 THC-dominant clone lines from 14 varieties were sampled in
the GM Pharmaceuticals’ glasshouses at the sixth, eighth, and tenth weeks flow-
ering . With a 33% extension in flowering duration from the sixth to eighth
week, mean THC yield (g/m2) increased over 50%. With 25% extension in flow-
ering period from the eighth to ten weeks, mean THC yield (g/m2) increased
30%, while the yield increases for approximately half of the clones were less than
25%. The mean THC and CBG content in floral and foliage material continu-
ously increased in the twenty-five clones between the sixth and tenth week of
flowering, while the mean proportion of CBG fell as a proportion of total THC
and CBG. This suggests that the ratio of these two cannabinoids can be affected
by harvest timing. Furthermore, genetics impact THC:CBG ratios more than
harvest timing because the THC:CBG ratio of one clone was stable at all harvest
D. Jin et al.
10.4236/ajps.2019.106067 934 American Journal of Plant Sciences
timings whereas the average THC:CBG ratios combined from three harvest dates
(six, eight, ten weeks) showed significant differences between clone lines. The
effect of flowering period length on mixed THC/CBD profiles were studied on
five clone lines from five seeds of one variety. THC and CBD content in floral
and foliage material continuously increased from the fourth week to eighth week
in 12-hour light regime but stopped increasing after the ninth week. For one of
the clone lines, the CBD/THC ratio remained constant over the entire flowering
stage whereas the ratio fluctuated in other clone lines. Potter concluded that the
clone lines with stable CBD/THC ratio can be used as phytopharmaceutical
feedstocks and, if such clones are absent, desirable consistent cannabinoid mix-
tures could only be achieved by blending materials possessing one single domi-
nant cannabinoid. THC dominant Sativex plants grown in the GM Pharmaceu-
ticals’ glasshouses were normally harvested at eight weeks after switch to a
12-hour light regime. While the THC content in floral tissue was relatively stable
(13% - 17%) between the fourth week and ninth week with highest value achieved
around six weeks in short day length, the floral yield per plant increases steadily
until the end of cultivation, which is 400 g/m2 of floral material combined with
200 g/m2 of foliage material.
Another study concluded that the peak total THC content (THC + THCA) in
floral material was achieved between the sixth and seventh week after changing
to a 12-hour regime in an indoor grow box and the total THC content started to
decline at the onset of senescence in all three chemotype I varieties . Aizpu-
rua-Olaizola (2016) observed that plants from chemotypes II and III needed
more time to reach peak production of THCA, CBDA, and monoterpenes than
plants from chemotype I . Clones from all chemotypes were kept for 42 days
for root-growing phase, followed by 60 days for vegetative stages under 18 hours
of light and 77 days for flowering phase under 12 hours of light . THCA in
flowers of chemotype I plants peaked at the ninth week in short day length (day
165) for indoor growth, while peak content of THCA and CBDA in chemotype
II (THC and CBD with equivalent ratio) and chemotype III (CBD dominant)
continued to increase until the end of the study (eleventh week, or day 179). The
total amount of eight monoterpenes in flowers reached its peak in the ninth
week of the flowering phase for chemotype I while the levels continued to in-
crease until the end of the study for chemotype II and III. The amount of ses-
quiterpenes was stable during the flowering phase. Different maxima may de-
pend on cultivars, cultivation method (from seed or clone), and growing envi-
ronment (lighting, temperature, humidity, growing medium, nutrients, etc.).
Temperature can be a limiting factor for PN: Low temperatures
slow PN and excessive heat stops PN. High temperature causes plants to expend
energy in cooling by acquiring water and transpiring it through the stomata.
Chandra (2011) studied PN in seven cannabis varieties and concluded that the
optimal temperatures varied between 25˚C to 30˚C and were variety-specific
. The optimum growth temperature is 25˚C - 30˚C for tropical varieties and
25˚C for temperate varieties . In a field experiment on industrial hemp, Sikora
D. Jin et al.
10.4236/ajps.2019.106067 935 American Journal of Plant Sciences
calculated accumulative growing degree days (GDD) instead of daily tempera-
tures and found that THC and CBD concentrations are positively correlated
with GDD . However, the authors assumed a linear relationship between
climate and the content of major cannabinoids, resulting in poor statistical re-
gression between GDD and THC & CBD content. Four varieties from both
temperate (Illinois and Nepal) and tropical (Jamaica and Panama) climates
yielded higher THC content (mg/g dry weight) in cannabis leaves under cool
conditions (23˚C) than under warm conditions (32˚C) .
Carbon dioxide (CO2) is one of the two limiting factors
for PN. A high potency Mexican drug-type variety was exposed to different con-
centrations of CO2 (250, 350, 450, 550, 650, and 750 µmol/mol) under optimum
lightning and temperature conditions (30˚C and 1500 μmol/m2/s PPFD) .
Elevated CO2 concentration (750 µmol/mol) increased PN, WUE, and intercellu-
lar CO2 concentration (Ci) by 50%, 111%, and 115% respectively and suppressed
the rate of transpiration E and gs by 29% and 42% respectively compared to am-
bient CO2 (Ca: 350 µmol/mol) . Higher PN, WUE, and nearly constant Ci/Ca
under elevated CO2 concentrations suggested a potential for better survival,
growth, and productivity in CO2 rich environments .
. Compared to relative or absolute humidity, vapor pressure deficit
(VPD) more accurately describes the driving force of water loss from plant
leaves. VPD combines the relative humidity and air temperature and describes
the difference between the actual and maximum amounts of water the air can
hold for a given temperature. VPD impacts the opening of leaf stomata, which
are responsible for CO2 and water vapor exchange, thereby affecting PN and nu-
trient transportation. High VPD may induce wilt and necrosis of the leaf tips.
For indoor cultivation, ventilation is crucial to control humidity because both
high and low VPD can result in reduced yield . At a growing temperature of
25˚C, the recommended relative humidity is 75% for juvenile cannabis plants
and 55% - 60% for vegetative growth and flowering , which correspond to
VPD of 0.8 kPa and 1.3 - 1.4 kPa respectively. VPD is calculated using the fol-
lowing formula :
VPD 1 610.7 10
is the atmospheric temperature in centigrade and
is relative humid-
A review of several works reported an increased THC content in drier cli-
mates, which was explained as an enhanced THC production in response to
stress . A recent experiment confirmed that controlled drought stress may be
an effective horticultural management technique to maximize both floral weight
and cannabinoid yield in cannabis . An eleven-day drought (withholding ir-
rigation until the drought stress threshold of −1.5 MPa was reached at week
seven of the flowering stage) increased the concentration of major cannabinoids
THCA and CBDA by 12% and 13%, respectively. In Chemotype II plants, yield
per unit growing area of THC was 43% higher, CBDA yield was 47% higher,
D. Jin et al.
10.4236/ajps.2019.106067 936 American Journal of Plant Sciences
THC yield was 50% higher, and CBD yield was 67% higher than the control. A
follow-up investigation directly contradicted these results: drought stress timing
and frequency (in weeks four, five, six, or seven weeks in the flowering stage) did
not result in higher floral yield or cannabinoid content compared with the con-
trol . The author attributed the differences to the container size and growing
medium—the follow-up study used larger growing vessels than the previous
trial, so it took longer for a plant to deplete the water already in the vessel to
achieve drought conditions. The timing of controlled drought stress was found
to influence the content of some terpenoids. Earlier drought stress increased the
yield of linalool and cis-ocimene but decreased yield of caryophyllene. Later
drought stress increased the yield of alpha-bisabolol and trans-ocimene.
Both soil and soilless (i.e. hydroponics) mediums are used
for cannabis production. AHP recommends neutral to alkaline loamy and sandy
soil with a pH between 6.5 and 7.2 . One study grew cannabis in eleven dif-
ferent soils that varied in pH and elemental composition . Soil parameters
were correlated with the leaves’ elemental and cannabinoid contents. Extractable
soil Mg was negatively correlated with THC and CBD concentrations in leaf tis-
sue. Extractable soil P was negatively correlated with CBD concentrations in leaf
tissue . Another study showed that there was no difference in floral material
yield between two organic coir-based growing media, which had distinct wa-
ter-holding capacities . However, the lower capacity (U2-HP) growing me-
dium produced 11% higher floral dry weight, 13% higher growth index, 20%
higher THC yield, and 20% higher CBGA yield than the one with higher capac-
ity (U2) . The increases may be attributed to the higher irrigation frequency
(17 times in U2-HP and 13 times in U2), which was necessary for maintaining
moisture (30%), and/or high root zone oxygen, which positively affects plant
health, nutrient uptake, root growth, and root-bone disease prevention .
Hydroponic systems have greater control over the growing environment by de-
livering a full range of nutrients to the roots. Active hydroponic systems use
pumps and include ebb and flow systems, nutrient film technique, drip irriga-
tion, aeroponics, and deep-water-culture systems. Passive systems use capillary
action to drag water to the roots and these include reservoir systems, wick sys-
tems, and capillary mats. Commonly used growing media for hydroponic sys-
tems include light expanded clay aggregate (referred to as LECA), rock wool,
and coconut fibre (coir).
Both soil and hydroponics are widely used for commercial cultivation, and
each has its own advantages and disadvantages. Soil has a greater buffer capacity
than hydroponics and is simpler to set up. Hydroponic systems allow for com-
prehensive control, enabling quicker and easier troubleshooting for nutrient de-
livery. With easy access to nutrients and water, plants are commonly believed to
grow faster and have higher yields with hydroponics. However, evidence sug-
gested that yields and potency are not improved by hydroponics compared to
soil systems . In addition, a hydroponics system is more complex and re-
quires constant availability of water, electricity, nutrients, and other supplies.
D. Jin et al.
10.4236/ajps.2019.106067 937 American Journal of Plant Sciences
The increased complexity without corresponding increases in cannabis produc-
tivity or potency led to GW Pharmaceuticals’ rejection of hydroponic growing
systems in the Netherlands .
1.2. Management Practices
Seeds vs. clones.
Two starting materials are available: seeds and clones. Clones
are made from tissue cultures by micropropagation or from cuttings of a mother
plant. Clones guarantee genetic uniformity, which the pharmaceutical industry
values for consistency of quality, safety, and efficacy—qualities that the industry
regards as more important than high yield . Clones can also avoid the de-
velopment of male plants that can be encountered when starting from seeds .
To compare the yield and uniformity of plants grown from seeds and clones,
Potter grew thirty plants from cuttings and thirty plants from seeds of one vari-
ety under identical environmental conditions. The yield of floral and foliage
material obtained from plants grown from seeds (494 g/m2) and those grown
from cuttings (515 g/m2) were not significantly different (p > 0.05). However,
the mean THC content of the cloned plants (14.6% THC w/w) was significantly
higher than those grown from seeds (11.1% THC) (p < 0.01). Although the mean
CBG and CBC content in floral and foliage has no significant differences (p >
0.05) from plants grown from seeds and grown from cuttings, the CBC potency
of seed derived plants was significantly more variable (p < 0.01).The ratios of
cannabinoids were also found to be significantly more variable in plants grown
from seeds (p < 0.01). However, it was not discussed whether the variability re-
sulted from the uniformity of the heterozygous seeds or homozygous seeds.
Furthermore, to achieve maximum rooting success and root quality, cuttings
from either apical or basal positions (p > 0.05) should have at least three fully
expanded (compared with having two leaves) and uncut leaves (compared with
removing the leaf tip), and treated with 0.2% indole-3-butyric (IBA) rooting
hormone (compared with treating with 0.2% willow extract gel) . Among
these factors, rooting hormone had the greatest effect on both rooting success
rate and root quality while removing leaf tips had the second greatest effect on
rooting success rate.
. Water quality is critical for PN and its products and nutrient trans-
port. For greenhouse crops, the water should be absent of contamination from
metals, herbicides, pesticides, and toxicologically hazardous substances . In
addition, irrigation water should be tested for the following desirable parame-
ters: alkalinity (expressed as CaCO3 concentration), pH, and electrical conduc-
tivity (EC) . The recommended parameters vary greatly among different
strains. The optimal EC or pH for cannabis in soil or hydroponic systems has yet
to be established through experimentation. General recommendations for irrigation
are CaCO3 concentrations between 30 mg/L and 100 mg/L, EC below 1.5 mS/cm,
and hardness as Ca and Mg ions between 100 mg/L to 150 mg/L . AHP rec-
ommends that the pH in irrigation water should be 6.5 - 7.2 for soil and 5.8 - 6.0
D. Jin et al.
10.4236/ajps.2019.106067 938 American Journal of Plant Sciences
for hydroponics . The pH should be continuously monitored and adjusted
whenever it deviates from the set point. Watering frequency and amount can be
visually determined or automated to satisfy plant requirements   .
If the growing medium lacks nutrients, it must be supple-
mented to ensure the plants’ health and yield. Different fertilizers may be used
or mixed in accordance with different growth cycles, however, organic fertilizers
are not recommended for hydroponic systems because they ferment in the res-
ervoirs, causing microbiological contamination and clogging.
Several studies analyzed the effect of applied fertilizers on morphological and
biochemical characteristics of cannabis plants. One study analyzed responses of
greenhouse-grown cannabis to N, P, and K at low (0 ppm), medium (25 ppm for
N and 50 ppm for P and K), and high concentrations (125 ppm for N and 150
ppm for P and K) . Fertilizers were applied during planting. Mean height (at
28 days and harvest) and tissue yield (combined leaves and flowers) were posi-
tively correlated with applied P at three concentrations but were not statistically
significant for applied N or K. Although THC and CBD concentrations showed
no significant differences after treatment with applied P, N, and K (p > 0.05), to-
tal THC yield was significantly positively correlated with applied P due to in-
creased biomass (p < 0.05). In a study where three levels of N fertilizer were ap-
plied once each month with totals of 150, 450, and 600 mg/kg, applied N had a
positive effect on plant height and a negative effect on THC content (% dry
weight) in leaves . Mg and Fe were reported to be important for THC pro-
duction as enzyme co-factors .
Caplan sought to determine the optimal rate of organic fertilizer during vege-
tative and flowering stages for cannabis grown in coir-based growing media. The
study applied liquid fertilizer with a N-P-K ratio of 4:1.3:1.7 at rates of 117, 234,
351, 468, and 585 mg nitrogen per litre of irrigation water (N/L) during vegeta-
tive growth and found that the interpolated optimal rate was 389 mg N/L. This
optimal rate increased the yield of floral dry weight by 80% as compared to 117
mg N/L . The final yield was positively correlated with growth attributes
(growth index [height (cm) × length (cm) × width (cm) × 300−1], leaf number,
and branch number) in the vegetative stage . This result suggests that grow-
ing larger plants during the vegetative stage by supplying optimal fertilizer rate
will increase yield . The study also concluded that fertilization rate had no
effect on floral THCA concentrations (10.6% ± 0.31%) or CBN concentrations
(0.08% ± 0.018%) but increased THC concentrations, reaching a maximum of
0.31% at 418 mg N/L . Optimal fertilization during the vegetative stage may
reduce maturation time .
The same study applied five rates of liquid organic fertilizer (57, 113, 170, 226,
and 283 mg N/L) with a N-P-K ratio of 2.00:0.87:3.32 during the flowering stage
in two coir-based growing media . Fertilizer rate was positively correlated
with floral yield. In the medium with lower water-holding capacity (U2-HP), the
interpolated optimal rate (261 mg N/L) increased the yield of floral dry weight
by 110% compared to the lowest rate (57 mg N/L). Similar results were found for
D. Jin et al.
10.4236/ajps.2019.106067 939 American Journal of Plant Sciences
the other medium. Although growth and floral yield are increased with fertilizer
rate, concentrations of THC, THCA, and CBGA decreased. The optimal fertil-
izer rate for U2-HP for maximizing both floral yield and cannabinoid yield was
between 212 and 261 mg N/L.
Growing medium management.
The condition of the growing medium is de-
pendent on the primary inputs: irrigation and fertilization. Caplan’s experiment
showed that growing medium pH decreased over time for all fertilizer rates ap-
plied during vegetative growth . The highest floral yield, which supplied 234,
351, and 468 mg N/L, resulted in the lowest pH values, which were between 6.19
and 6.5, with lowest mean pH (6.19) occurring at 351 mg N/L rate on day 17
. The low pH values for organic fertilizers may be caused by
tion and the excretion of protons by the roots after
uptake . This
study showed no visual signs of nutrient disorders with pH between 6.2 - 7.1 for
the vegetative stage and 6.7 - 7.2 for the flowering stage. EC was positively cor-
related with fertilization, ranging from 0.9 to 3.9 mS/cm . Floral yield was
reduced at 468 and 585 mg N/L, and was attributed to high EC, which was 3.0 ±
0.13 and 3.8 ± 0.13 mS/cm, respectively. Salinity is expressed in EC and can lead
to increased osmotic potential and reduced external water potential in the root
zone. The pH decreased and EC increased upon higher rates of fertilizer applica-
tion during flowering . The study concluded that cannabis tolerates EC up to
3.0 mS/cm without reductions in yield.
Pruning and training.
Pruning and training enhance yield by maximizing light
interception, optimizing nutrient allocation, creating more air circulation, and
reducing humidity. Clipping the lower branches on the Bedrocan variety (hybrid
“Indica”/“Sativa”), which were grown under 37 days of vegetative stage and 54
days of flowering stage, resulted in lower concentrations for THC, CBG and
some terpenes . Additional studies need to be conducted to quantitatively
determine the effects of pruning timing and amount on growth and yield.
Another technique uses framed netting to support and position buds in an
“opened-up” gesture to provide more light to the lower branches. Knight utilized
the ScrOG method, which uses framed netting, to enhance yield of an indoor
hydroponic system . An average of 687 g dried inflorescence was achieved
per plant using this method. This relatively high yield per plant maybe due to the
characteristics of the strains selected and the relatively low plant density (6
plants in 15 m2). The estimated yield per area was 274.8 g/m2 and was compara-
ble to yields reported in other studies .
Because the content of cannabinoids and terpenes change
throughout growing and flowering stages, harvest timing affects final chemical
composition. To determine specific harvest timing, two methods are commonly
used by growers: chemical analysis and visually observation/organoleptic evalua-
tion. The University of Mississippi checks THCA concentrations of raw materi-
als daily to determine optimal harvest time . Whereas chemical analysis is de-
structive, visual examination is adopted to set harvest timing without disturbing
the plants. AHP suggests four physical evaluations. The first evaluation is based
D. Jin et al.
10.4236/ajps.2019.106067 940 American Journal of Plant Sciences
on the percentage of senesced stigmas, which appear brown. The percentage at
harvest is suggested as 75% . The second evaluation is based on the firmness
of the inflorescence—relatively firm resistance when pressed suggested maturity.
The third evaluation is based on the color of glandular trichomes. Harvest
should occur when there is a shift from a clear to amber or a cloudy white of the
first resin heads, which indicates the degradation of THC to CBN. The last
evaluation is based on odor, which will reach a peak and give a unique and
strain-specific pungent aroma at maturity. These methods can be combined to
determine optimal harvest timing .
After harvesting cannabis, it is manicured, cured, dried, and stored. Fresh can-
nabis material typically contains 78-80% moisture  and drying is necessary
for handling, storage, and avoiding degradation of major cannabinoids before
chemical examination. The Office of Medicinal Cannabis of the Dutch Govern-
ment specifies that the water content of cannabis must be between 5% - 10% di-
rectly after packing . Drying crops directly on the ground or under direct
sunshine must be avoided . Plants dry within 24 hours to 15% ± 2% mois-
ture when spread evenly to a depth of approximately 15 cm at 40˚C . Mois-
ture content can be checked by measuring weight loss after drying for 24 hours
at 105˚C. If the plants are hung to dry, the mean times taken to achieve 15%
moisture were 36, 18, and 11 hours at 30˚C, 40˚C, and 50˚C, respectively .
When stored in paper bags to dry at 21˚C and 40% RH, fresh floral material cut
from stems reached 11% ± 1% moisture in 5 days . The dried material was
then cured at 18˚C and 60% RH for 14 days before determining the floral dry
weight . Drying at temperature higher than 37˚C for 24 hours may decar-
boxylate cannabinoid acids . The effect of high drying temperatures on can-
nabinoids and terpenes requires further investigation. To minimize loss of vola-
tile terpenes during heating, another method for cannabinoid and terpene pres-
ervation is freezing by sublimation, which takes 10 to 20 days.
As oxidation occurs with the presence of light, heat, and oxygen, degradation
of major cannabinoids is minimized after drying by storage in cool and dark
places. Fresh products must be stored between 1˚C and 5˚C and frozen products
must be kept at −18˚C to −20˚C for long-term storage . The content of THC
stored at −18˚C, 4˚C, and 22˚C ± 1˚C decomposed at rates of 3.83%, 5.38%, and
6.92% per year, respectively . Samples can be stored at −18˚C or 4˚C for
about 30 weeks before concentrations of THCA and THC change, however,
samples stored at 22˚C ± 1˚C showed some immediate decomposition. Dried
samples stored at 50˚C for 24 hours showed slight decarboxylation while those
stored at 100˚C and 150˚C showed significant decarboxylation of THCA and
decomposition of THC within two hours . The effect of freeze-drying on
terpenes has not been well-studied, but reportedly fails to preserve the profile of
the fresh plant by changing terpene concentrations .
D. Jin et al.
10.4236/ajps.2019.106067 941 American Journal of Plant Sciences
Cannabis standardization is required to obtain consistent cannabinoid and ter-
pene profiles and, subsequently, stable efficacy for medical purposes. Growing
conditions and management practices should be optimized and standardized to
maximize yields; light, temperature, CO2 concentration, irrigation, humidity,
nutrients, and growing media combine and interact to affect the final yield.
The effects of LED should be compared with traditional lamps used in canna-
bis cultivation in terms of cannabis yield and electricity consumption. The ef-
fects of near-visible light, especially UV, on yield require additional data to form
conclusions. Light intensity studies have been conducted with conclusive results,
but comparisons between studies are hampered by the differences in controlled
variables between experiments. Optimal light conditions for cannabis should be
researched under controlled environments to determine the optimized combina-
tion of light intensity with plant density for maximum plant yield. Light inter-
ception and plant growing density may affect the development rate of inflores-
cences, however, current research yields conflicting results. Optimal growing
temperatures for cannabis are believed to be associated with the cultivars’ geo-
graphic origins. Studies that control for temperature are lacking.
The pH value recommendations in growing media vary in current literature.
Watering amount and frequency is not well specified. Fertilizers have many
variables and the effects of content, elemental ratio, and frequency of fertiliza-
tion on yield are unclear. Analyzing the effects of the dozens of interacting vari-
ables of the nutrient in growing media will be a significant undertaking and will
require large amounts of indoor growing space to control for individual vari-
ables. Studies comparing the yield and quality of cannabis cultivation in soil and
hydroponic systems are still lacking.
Details on pruning and training are limited. The effects of different pruning
and training techniques, including pruning lower leaves during vegetative stage,
clipping or inverting the top to make the plant bushy, utilization of framed net-
ting or ScrOG methods needs to be examined in controlled studies. Harvest
timing is subjective and must be examined on a case-by-case basis. Due to the
large number of variables, it may not be possible to determine exact harvest
times for cannabis. The fluctuation of cannabinoids and terpenes throughout a
24-hour cycle needs further research. Post-harvest treatment, especially drying
temperature and duration, should be studied for the effects on cannabinoids and
Current industrial practices for growing conditions vary significantly, and
certain aspects of harvest can be subjective. Additional research and studies are
required to conclusively develop a set of optimal and standardized growing con-
ditions and harvest techniques.
The authors acknowledge Labs-Mart Inc. for providing funding during the
D. Jin et al.
10.4236/ajps.2019.106067 942 American Journal of Plant Sciences
preparation of this manuscript. We are also grateful to Dr. Tiequan Zhang from
Agriculture and Agri-Food Canada and Dr. Thomas Graham from the Univer-
sity of Guelph for providing valuable comments and suggestions.
Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this pa-
 ElSohly, M.A., Gul, W., Wanas, A.S. and Radwan, M.M. (2014) Synthetic Cannabi-
noids: Analysis and Metabolites.
, 97, 78-90.
 Upton, R., Craker, L., ElSohly, M., Romm, A., Russo, E., Sexton, M.,
Cannabis Inflorescence: Cannabis Spp. ; Standards of Identity, Analysis, and Quality
Control. American Herbal Pharmacopoeia, Scotts Valley, CA.
 Taura, F., Morimoto, S., Shoyama, Y. and Mechoulam, R. (1995) First Direct Evi-
dence for the Mechanism of Delta-1-Tetrahydrocannabinolic Acid Biosynthesis.
Journal of the American Chemical Society
, 117, 9766-9767.
 Taura, F., Morimoto, S. and Shoyama, Y. (1996) Purification and Characterization
of Cannabidiolic-Acid Synthase from
L.: Biochemical Analysis of a
Novel Enzyme That Catalyzes the Oxidocyclization of Cannabigerolic Acid to Can-
Journal of Biological Chemistry
, 271, 17411-17416.
 Morimoto, S., Komatsu, K., Taura, F. and Shoyama, Y. (1997) Enzymological Evi-
dence for Cannabichromenic Acid Biosynthesis.
Journal of Natural Products
 Fellermeier, M. and Zenk, M.H. (1998) Prenylation of Olivetolate by a Hemp
Transferase Yields Cannabigerolic Acid, the Precursor of Tetrahydrocannabinol.
, 427, 283-285. https://doi.org/10.1016/S0014-5793(98)00450-5
 Fellermeier, M., Eisenreich, W., Bacher, A. and Zenk, M.H. (2001) Biosynthesis of
Cannabinoids. Incorporation Experiments with 13C-Labeled Glucoses.
Journal of Biochemistry
, 268, 1596-1604.
 Hazekamp, A. (2007) Cannabis: Extracting the Medicine. Print Partners Ipskamp,
 Russo, E.B. (2011) Taming THC: Potential Cannabis Synergy and Phytocannabi-
noid-Terpenoid Entourage Effects.
British Journal of Pharmacology
, 163, 1344-1364.
 Jin, D., Jin, S., Yu, Y., Lee, C. and Chen, J. (2017) Classification of Cannabis Culti-
vars Marketed in Canada for Medical Purposes by Quantification of Cannabinoids
and Terpenes Using HPLC-DAD and GC-MS.
Journal of Analytical & Bioanalytical
, 8, 349. https://doi.org/10.4172/2155-9872.1000349
 Health Canada (2013) Information for Health Care Professionals: Cannabis (Mari-
huana, Marijuana) and the Cannabinoids.
 Potter, D.J. (2014) A Review of the Cultivation and Processing of Cannabis (
L.) for Production of Prescription Medicines in the UK.
Drug Testing and
D. Jin et al.
10.4236/ajps.2019.106067 943 American Journal of Plant Sciences
, 6, 31-38. https://doi.org/10.1002/dta.1531
 Fetterman, P.S., Keith, E.S., Waller, C.W., Guerrero, O., Doorenbos, N.J. and
Quimby, M.W. (1971) Mississippi-Grown
L.: Preliminary Observa-
tion on Chemical Definition of Phenotype and Variations in Tetrahydrocannabinol
Age, Sex, and Plant Part.
Journal of Pharmaceutical Sciences
 De Meijer, E.P.M. (2014) The Chemical Phenotypes (Chemotypes) of Cannabis. In:
Pertwee, R., Ed.,
Handbook of Cannabis
, Oxford University Press, Oxford, 89-110.
 Pacifico, D., Miselli, F., Carboni, A., Moschella, A. and Mandolino, G. (2008) Time
Course of Cannabinoid Accumulation and Chemotype Development during the
, 160, 231-240.
 De Backer, B., Maebe, K., Verstraete, A.G. and Charlier, C. (2012) Evolution of the
Content of THC and Other Major Cannabinoids in Drug Type Cannabis Cuttings
and Seedlings during Growth of Plants.
Journal of Forensic Sciences
, 57, 918-922.
 Aizpurua-Olaizola, O.S. (2016) Evolution of the Cannabinoid and Terpene Content
during the Growth of
Plants from Different Chemotypes.
, 79, 324-331. https://doi.org/10.1021/acs.jnatprod.5b00949
 United Nations Office on Drugs and Crime (2009) Recommended Methods for the
Identification and Analysis of Cannabis and Cannabis Products. United Nations,
 Hillig, K. (2002) Letter to the Editor.
Journal of Industrial Hemp
, 7, 5-6.
 Clarke, R. and Merlin, M. (2016) Cannabis: Evolution and Ethnobotany. University
of California Press, Oakland, CA.
 Office of Medicinal Cannabis (2003) Guidelines for Cultivating Cannabis for Me-
 Sabeh, N. (2017) Maximizing Profitability: By Managing Plant-Environment Inter-
Marijuana Venture Magazine
 Magagnini, G., Grassi, G. and Kotiranta, S. (2018) The Effect of Light Spectrum on
the Morphology and Cannabinoid Content of
, 1, 19-27. https://doi.org/10.1159/000489030
 Malloy, K.D., Holman, M.A., Mitchell, D. and Detrich, H.W. (1997) Solar
UVB-Induced DNA Damage and Photoenzymatic DNA Repair in Antarctic Zoo-
Proceedings of the National Academy of Sciences of the United States of
, 94, 1258-1263. https://doi.org/10.1073/pnas.94.4.1258
 Ahmed, F.E. and Setlow, R.B. (1993) Ultraviolet Radiation-Induced DNA Damage
and Its Photorepair in the Skin of the Platyfish Xiphophorus.
 Pate, D.W. (1983) Possible Role of Ultraviolet Radiation in Evolution of
, 37, 396-405. https://doi.org/10.1007/BF02904200
 Pate, D.W. (1994) Chemical Ecology of Cannabis.
Journal of the International
, 2, 32-37.
 Lydon, J., Teramura, A.H. and Coffman, C.B. (1987) UV-B Radiation Effects on
Photosynthesis, Growth and Cannabinoid Production of Two
Photochemistry and Photobiology
, 46, 201-206.
D. Jin et al.
10.4236/ajps.2019.106067 944 American Journal of Plant Sciences
 Vanhove, W., Van Damme, P. and Meert, N. (2011) Factors Determining Yield and
Quality of Illicit Indoor Cannabis (
Forensic Science In-
, 212, 158-163. https://doi.org/10.1016/j.forsciint.2011.06.006
 Hawley, D., Graham, T., Stasiak, M. and Dixon, M. (2018) Improving Cannabis Bud
Quality and Yield with Subcanopy Lighting.
, 53, 1593-1599.
 Zelitch, I. (1975) Improving the Efficiency of Photosynthesis.
, 188, 626-633.
 Chandra, S., Lata, H., Khan, I.A. and ElSohly, M.A. (2008) Photosynthetic Response
L. to Variations in Photosynthetic Photon Flux Densities, Tem-
perature and CO2 Conditions.
Physiology and Molecular Biology of Plants
 Chandra, S., Lata, H., Khan, I.A. and ElSohly, M.A. (2011) Temperature Response
of Photosynthesis in Different Drug and Fiber Varieties of
ology and Molecular Biology of Plants
, 17, 297.
 Chandra, S., Lata, H., Mehmedic, Z., Khan, I.A. and ElSohly, M.A. (2015) Light
Dependence of Photosynthesis and Water Vapor Exchange Characteristics in Dif-
9-THC Yielding Varieties of
Journal of Applied Re-
search on Medicinal and Aromatic Plants
, 2, 39-47.
 Potter, D.J. (2009) The Propagation, Characterisation and Optimisation of Canna-
bis Sativa L as a Phytopharmaceutical. Ph.D. Thesis, King’s College, London.
 Monteith, J.L. and Moss, C.J. (1977) Climate and the Efficiency of Crop Production
Philosophical Transactions of the Royal Society of London B
, 281, 277-294. https://doi.org/10.1098/rstb.1977.0140
 Langhans, R.W. and Tibbitts, T.W. Growth Chamber Handbook—NCERA-101.
North Central Regional Research Publication No. 340.
 Potter, D.J. and Duncombe, P. (2012) The Effect of Electrical Lighting Power and
Irradiance on Indoor-Grown Cannabis Potency and Yield.
Journal of Forensic Sci-
, 57, 618-622. https://doi.org/10.1111/j.1556-4029.2011.02024.x
 European Monitoring Centre for Drugs and Drug Addiction (2012) Cannabis Pro-
duction and Markets in Europe.
 Clarke, R.C. (1981) Marijuana Botany. Ronin Publishing, San Francisco, CA.
 Nobel, P.S. (2005) Physicochemical and Environmental Plant Physiology. Academic
 Fischedick, J.T., Hazekamp, A., Erkelens, T., Choi, Y.H. and Verpoorte, R. (2010)
Metabolic Fingerprinting of
L., Cannabinoids and Terpenoids for
Chemotaxonomic and Drug Standardization Purposes.
, 71, 2058-
 Sikora, V., Berenji, J. and Latković, D. (2011) Influence of Agroclimatic Conditions
on Content of Main Cannabinoids in Industrial Hemp (
, 43, 449-456. https://doi.org/10.2298/GENSR1103449S
 Bazzaz, F.A., Dusek, D., Seigler, D.S. and Haney, A.W. (1975) Photosynthesis and
Cannabinoid Content of Temperate and Tropical Populations of
Biochemical Systematics and Ecology
, 3, 15-18.
D. Jin et al.
10.4236/ajps.2019.106067 945 American Journal of Plant Sciences
 Chandra, S., Lata, H., Khan, I.A. and ElSohly, M.A. (2013) The Role of Biotech-
Propagation for the Production of Phytocannabinoids.
In: Chandra, S., Lata, H. and Varma, A., Eds.,
Biotechnology for Medicinal Plants
Springer, Berlin, Heidelberg, 123-148.
 Monteith, J. and Unsworth, M. (2013) Principles of Environmental Physics: Plants,
Animals, and the Atmosphere. Academic Press, Cambridge, MA.
 Caplan, D.M. (2018) Propagation and Root Zone Management for Controlled En-
vironment Cannabis Production. Ph.D. Thesis, University of Guelph, Guelph
and Toronto, Ontario.
 Coffman, C.B. and Gentner, W.A. (1975) Cannabinoid Profile and Elemental Up-
L. as Influenced by Soil Characteristics.
67, 491-497. https://doi.org/10.2134/agronj1975.00021962006700040010x
 Caplan, D., Dixon, M. and Zheng, Y. (2017) Optimal Rate of Organic Fertilizer
during the Vegetative-Stage for Cannabis Grown in Two Coir-Based Substrates.
, 52, 1307-1312. https://doi.org/10.21273/HORTSCI11903-17
 Chen, J., Beeson Jr., R.C., Yeager, T.H., Stamps, R.H. and Felter, L.A. (2003)
Evaluation of Captured Rainwater and Irrigation Runoff for Greenhouse Foliage
and Bedding Plant Production.
, 38, 228-233.
 Swistock, B. (2016) Interpreting Irrigation Water Tests. Penn State Extension.
 Bruci, Z., Papoutsis, I., Athanaselis, S., Nikolaou, P., Pazari, E., Spiliopoulou, C. and
Vyshka, G. (2012) First Systematic Evaluation of the Potency of
Plants Grown in Albania.
Forensic Science International
, 222, 40-46.
 Vanhove, W. (2014) The Agronomy and Economy of Illicit Indoor Cannabis Culti-
vation. Ghent University, Ghent, Belgium.
 Coffman, C.B. and Gentner, W.A. (1977) Responses of Greenhouse-Grown
L. to Nitrogen, Phosphorus, and Potassium.
, 69, 832-
 Bócsa, I., Máthé, P. and Hangyel, L. (1997) Effect of Nitrogen on Tetrahydrocan-
nabinol (THC) Content in Hemp (
L.) Leaves at Different Positions.
Journal of the International Hemp Association
, 4, 78-79.
 Knight, G., Hansen, S., Connor, M., Poulsen, H., McGovern, C. and Stacey, J. (2010)
The Results of an Experimental Indoor Hydroponic
Growing Study, Us-
ing the ‘Screen of Green’ (ScrOG) Method—Yield, Tetrahydrocannabinol (THC)
and DNA Analysis.
Forensic Science International
, 202, 36-44.
 Hazekamp, A., Sijrier, P. and Verpoorte, R. (2006) An Evaluation of the Quality of
Medicinal Grade Cannabis in the Netherlands.
, 1, 1-9.
 Turner, J.C. and Mahlberg, P.G. (1984) Effects of Sample Treatment on Chroma-
tographic Analysis of Cannabinoids in
, 283, 165-171. https://doi.org/10.1016/S0021-9673(00)96251-4
 Turner, C.E., Hadley, K.W., Fetterman, P.S., Doorenbos, N.J., Quimby, M.W. and
Waller, C. (1973) Constituents of
L. IV: Stability of Cannabinoids
in Stored Plant Material.
Journal of Pharmaceutical Sciences
, 62, 1601-1605.
D. Jin et al.
10.4236/ajps.2019.106067 946 American Journal of Plant Sciences
 Taschwer, M. and Schmid, M.G. (2015) Determination of the Relative Percentage
Distribution of THCA and
9-THC in Herbal Cannabis Seized in Austria-Impact of
Different Storage Temperatures on Stability.
Forensic Science International
 Abascal, K., Ganora, L. and Yarnell, E. (2005) The Effect of Freeze Drying and Its
Implications for Botanical Medicine: A Review.
, 19, 655-660.