HORTSCIENCE 52(9):1307–1312. 2017. doi: 10.21273/HORTSCI11903-17 but the medicinal effects of CBD have re- cently been identified (Russo, 2011) leading some breeders to select for high CBD. Most Optimal Rate of Organic Fertilizer indoor production of cannabis occurs in two growth stages, vegetative and flowering, during the Vegetative-stage for which are controlled by photoperiod (Farag and Kayser, 2015). Modern day cultivation of Cannabis Grown in Two Coir-based cannabis takes place almost exclusively in- doors under artificial lighting using either solution culture systems or soilless growing Substrates substrates (Leggett, 2006; Potter, 2014). In Deron Caplan, Mike Dixon, and Youbin Zheng1 addition, many cannabis growers favor or- School of Environmental Sciences, University of Guelph, Guelph, ON N1G ganic production practices because consumers 2W1, Canada and regulating bodies often demand pesticide- free cannabis (Canada Gazette, 2016). Additional index words. Cannabis sativa, cannabis growth, floral dry weight, marijuana, THC, Online horticultural resources are avail- CBN able for cannabis production; however, lim- ited information is available in peer-reviewed Abstract. Cannabis producers, especially those with organic operations, lack reliable scientific literature. Furthermore, there is information on the fertilization requirements for their crops. To determine the optimal scant published scientific research on any organic fertilizer rate for vegetative-stage cannabis (Cannabis sativa L.), five rates that aspect of organic cannabis production. Be- supplied 117, 234, 351, 468, and 585 mg N/L of a liquid organic fertilizer (4.0N–1.3P– cause of a lack of systematic horticultural 1.7K) were applied to container-grown plants with one of two coir-based organic research, current cannabis producers rely substrates. The trial was conducted in a walk-in growth chamber and the two substrates on cultivation methods derived largely used were ABcann UNIMIX 1-HP with lower water-holding capacity (WHC) and from anecdotal information. Information on ABcann UNIMIX 1 with higher WHC. No differences in growth or floral dry weight fiber-type cannabis cultivation techniques (yield) were found between the two substrates. Pooled data from both substrates showed allows for some parallels to be drawn; how- that the highest yield was achieved at a rate that supplied 389 mg N/L (interpolated from ever, fiber-type cannabis is field-grown yield-fertilizer responses) which was 1.8 times higher than that of the lowest fertilizer and has been selectively bred for fiber pro- rate. The concentration of Δ9-tetrahydrocannabinol (THC) in dry floral material was duction rather than for essential oil content maximized at a rate that supplied 418 mg N/L, and no fertilizer rate effects were observed (Amaducci et al., 2015). A chemotaxonomic on D9-tetrahydrocannabidiolic acid (THCA) or cannabinol (CBN). The highest yield, study found low gene flow between drug- and cannabinoid content, and plant growth were achieved around an organic fertilizer rate fiber-type cannabis (Hillig and Mahlberg, that supplied 389 mg N/L during the vegetative growth stage when using the two coir- 2004) and was supported by a recent genomic based organic substrates. study comparing fiber and drug-type canna- bis (van Bakel et al., 2011). This makes it difficult to relate cultivation techniques be- Cannabis (Cannabis sativa L.) legislation use of cannabis became widespread, with tween the two crops (Amaducci et al., 2015). in North America continues to move rapidly evidence of cultivation and use in ancient Fertilization is one of the most important toward liberalization and in some instances Egypt around 2800 BCE and in China around factors for indoor organic cannabis produc- legalization, shifting cultivation from a largely 2000 BCE (Russo, 2007). The medicinal tion. For fiber-type cannabis, the suggested illicit practice to one that is not only legal, but value of cannabis is attributed primarily to fertilization rate is around 50–200 kg N/ha in high demand. In the United States, with a group of secondary metabolites called (Aubin et al., 2015; Ehrensing, 1998; Vera only a handful of states having legalized cannabinoids which are concentrated mostly et al., 2004), which is similar to other high- recreational cannabis as of 2017, the market in the essential oils of unfertilized female yielding field crops such as wheat (Triticum for legal cannabis was estimated at $2.7 billion flowers (Potter, 2014). spp.; Baxter and Scheifele, 2008). It is USD in 2014, and it is expected to reach $11 More than 100 unique cannabinoids have difficult, however, to estimate fertilizer re- billion by 2019 (ArcView Market Research been identified (Ahmed et al., 2008, 2015; quirements of drug-type cannabis based on and New Frontier, 2014). The current Cana- ElSohly and Slade, 2005), although Δ9-THC fiber-type cannabis or other crops because of dian government has pledged to follow suit and cannabidiol (CBD) are considered the the differences in species and growing con- and pass legislation to legalize cannabis for primary psychoactive and medicinal compo- ditions (Wright and Niemiera, 1987). Fur- recreational purposes beginning in spring of nents (Elzinga et al., 2015; Mechoulam et al., thermore, it is well-known that different 2017. Until then, current legislation allows 1970). In live plants, cannabinoids exist pri- growth stages of the same species have a limited number of private, licensed facilities marily as carboxylic acids such as D9-THCA varying nutrient demand; when the demand to produce and distribute cannabis for medic- and cannabidiolic acid (CBDA) (Muntendam is met, plant performance is improved (Raviv inal purposes as well as conduct scientific et al., 2012). These acids undergo decarbox- and Lieth, 2007; Wang, 2000). Most studies research (Canada Gazette, 2016). ylation during storage (Ross and ElSohly, on fertilizer application in other crops have Cannabis is an annual dioecious species, 1997; Taschwer and Schmid, 2015) and upon been conducted using conventional fertil- producing separate male and female plants. heating (Kimura and Okamoto, 1970) to izers, and there are few on the use of organic Archeological evidence of cultivation dates become neutral cannabinoids such as THC fertilizers for container crops. Fertigation to 10,000 BCE in China where cannabis was and CBD. Varieties of cannabis with low rates of 190–400 mg N/L have been reported used primarily for fiber. Later, the medicinal THC and high CBD are termed hemp or fiber- for container production of organic greenhouse- type cannabis, whereas those with high THC grown tomatoes (Solanum lycopersicum L.; and low CBD are termed marijuana or drug- Surrage et al., 2010; Zhai et al., 2009). To type cannabis, hereafter referred to as canna- our knowledge, neither organic nor conven- We thank ABcann Medicinals Inc. for providing bis (van Bakel et al., 2011; Vollner et al., tional fertilizer application rates have been funding as well as materials, expertise, and ground-level support. We would also like to thank 1986). Selective breeding has produced hun- published for indoor cannabis production in Millenniumsoils Coir and EZ-GRO Inc. for pro- dreds of varieties of cannabis with varying scientific literature. viding materials and technical support. chemical compositions and growth character- Appropriate choice of a growing substrate 1Corresponding author. E-mail: yzheng@uoguelph. istics (Vollner et al., 1986). Selection has is essential for soilless crop production be- ca. mostly been for high floral THC concentration, cause it directly affects root zone water, air,
HORTSCIENCE VOL. 52(9) SEPTEMBER 2017 1307 and nutrient availability and balance (Zheng, element concentrations of Nutri Plus Grow and leaves were trimmed thereafter. Floral 2016). While there are no experimental data were (in mg·L–1): 0.0 Ca, 0.0 Mg, 14.5 Zn, fresh weight was measured before the floral on growing substrates for cannabis, the in- 0.0 Mn, 12.0 B, 2.6 Mo, 2.1 Cu, and 8.5 Fe. material was placed in paper bags for drying formation we collected from the industry At the end of the vegetative growth period at 21 C and 40% RH for 5 d until moisture indicates that many North American canna- (21 d after transplanting), six plants with content reached 11 ± 1%. Dry material was bis producers are using either coir- or peat- representative height and canopy size from then cured at 18 C and 60% RH for 14 d based substrates, or inert substrates such as each treatment were selected and transferred before determining the floral dry weight rockwool. Different substrates have different into a growth chamber for the flowering (yield). physical and chemical properties; therefore, stage. Plants were potted into 6 L blow- Substrate electrical conductivity and pH it is essential to fertigate plants accordingly to molded black pots (22 cm diameter · 22 cm measurement. Substrate pH and electrical ensure an adequate root zone environment height) containing a custom blended organic conductivity (EC) were determined weekly (Zheng, 2016). growing substrate (60% sphagnum peat and using the pour-through method (Wright, The objective of this study was to de- 40% bulk coconut coir; Premier Tech, 1986) during the vegetative stage and at 4 termine the optimal organic fertilizer rates for Rivi ere-du-Loup, QC, Canada). Agricultural and 5 weeks of the flowering stage. Pour- growing vegetative-stage cannabis plants in dolomitic lime (Premier Tech) was incorpo- through solutions were measured for pH and two coir-based organic growing substrates in rated at a rate of 3.0 kg·m–3 of substrate. EC using a HI991300 portable pH/EC/TDS/ a controlled environment growth chamber. Plants were spaced on tables to a density of Temperature Meter (Hanna Instruments, 6.5 plants/m2. The PAR was maintained at Woonsocket, RI). Materials and Methods 500 ± 50 mmol·m–2·s–1 with a 12-h photo- Floral cannabinoid analysis. Dried, cured period. Irrigation was administered with one floral material was stored in dark and cool Plant culture and treatments. Seventeen- emitter per plant. During the first 11 d in the conditions according to United Nations Of- day-old rooted cuttings (10 cm high with flowering stage, plants were irrigated when- fice on Drugs and Crime (2009) before being 6 leaves) of cannabis ‘OG Kush · Grizzly’ ever the substrate moisture content reached analyzed by an independent laboratory (RPC were transplanted into round peat-based pots 30% with Nutri Plus Grow at a recommended Science and Engineering, Fredericton, NB, (9.5 cm diameter · 10.2 cm high) with one rate of 140 mg N/L and from then on with Canada). Cannabinoid analysis was per- plant per pot. Pots were filled with one of two a flowering specific fertilizer, Nutri Plus formed on the floral material of plants grown growing substrates, ABcann UNIMIX 1-HP Organic Bloom (2.00N–0.87P–3.32K; EZ- in U1 substrate. Analysis of the neutral (U1-HP) or ABcann UNIMIX 1 (U1) (Phys- GRO Inc.). Other nutrient element concen- cannabinoids THC, CBD, and CBN as well ical and chemical properties presented in trations in Nutri Plus Organic Bloom were (in as acid forms, THCA and CBDA were Tables 1 and 2, respectively; ABcann Me- mg·L–1): 0.0 Ca, 100.0 Mg, 10.0 Zn, 0.0 Mn, conducted by high-performance liquid chro- dicinals Inc., Napanee, Canada). The two 12.8 B, 0.1 Mo, 2.3 Cu, and 6.8 Fe. Nutri Plus matography as described in section 5.4.8 of organic substrates were coir-based and with Organic Bloom was administered at the United Nations Office on Drugs and Crime two distinct WHCs: U1-HP with lower WHC following manufacturer-recommended rates: (2009). and more drainage than U1. 77 mg N/L from day 12 to 19 in the flowering Statistical analysis. Data were analyzed Pots were randomly arranged in a growth stage, 103 mg N/L from day 20 to 27, and using JMP Statistical Discovery Version 13.0 chamber at a density of 97 plants/m2. The 129 mg N/L from day 28 to 39. Both (SAS Institute Inc., Cary, NC) at a Type 1 growth chamber was set at 22 C, 85% RH, vegetative and flowering fertilizers were error rate of #0.05. Full-factorial ANOVA –1 500 ppm CO2 (day and night), and a photo- amended with 2 mL·L of an organic with repeated measures was used to deter- synthetically active radiation (PAR)of calcium-magnesium supplement (3.0N–0.0P– mine the effects of substrate, fertilizer, and 250 ± 50 mmol·m–2·s–1 at canopy level with 0.0K–3.0Ca–1.6Mg; EZ-GRO Inc.). Between their interaction on substrate EC and pH as an 18-h photoperiod under fluorescent light- days 39 and 47 in the flowering stage, no well as growth index, leaf number, and ing. Beginning 3 d after transplant, plants fertilizer was applied and the substrates were branch number over time. Differences among were hand-fertigated with corresponding flushed, as per current industry practice, with means were tested with Tukey’s multiple nutrient solution to saturation with a 20% RO water: 10 L per pot at 7 d before harvest means comparison test. Two-way ANOVA leaching fraction when mean substrate mois- and 6 L at 5 d before harvest. was used to determine the effects of substrate, ture was 30%, measured using a WET-2 Growth and yield measurements. During fertilizer, and their interaction on yield and soil moisture sensor (Delta-T Devices Ltd., the vegetative stage, leaf number, canopy the effects of fertilizer on cannabinoid con- Cambridge, UK). This was considered the area, and plant height were measured every centrations. first day of treatment application. Plants were 7 d on five randomly selected plants from Pearson correlation coefficients were cal- rerandomized after each irrigation event. each treatment. Repeated measurements culated to determine if there is a relationship The experiment was a completely ran- were made on these same plants throughout between growth attributes and final yield. domized design with two factors: five fertil- the vegetative stage. During the flowering stage, Orthogonal partition and regression analysis izer rates and two substrate types, with 10 branch number, canopy area, and plant height (Bowley, 1999) were used to relate substrate replicates for each factor combination. Each were measured on all plants every 10 d. EC, pH, plant growth, yield, and cannabinoid potted plant was an experimental unit. Plants Growth index for each plant was calculated concentrations with fertilizer rate and/or were fertilized at one of the five rates of Nutri as height (cm) · length (cm) · width (cm) · yield. If the partitioning variance analysis Plus Organic Grow liquid organic fertilizer 300–1 (Ruter, 1992). Plants were harvested indicated a significant treatment effect, then (4.0N–1.3P–1.7K; Nutri Plus Grow; EZ-GRO after 47 d in the flowering stage on 14 Dec. the treatment effects were partitioned into Inc., Kingston, ON, Canada), supplying 117, 2015, when floral resin on most plants had one or more regression effects followed by an 234, 351, 468, or 585 mg N/L, diluted with 50% amber coloration. Stems were cut at estimation of regression parameters for the reverse osmosis (RO) water. Other nutrient soil level, floral material was cut from stems, best-fit regression. In all analyses, if there
Table 1. Physical properties of growing substrates ABcann UNIMIX 1-HP (U1-HP) and ABcann UNIMIX 1 (U1). Total porosityz CCz Air spacez Bulk densityz Growing substrate (%) (g·cm–3) U1-HP 93 ± 0.4 61 ± 1.2 31 ± 1.3 0.09 ± 0.001 U1 91 ± 0.3 72 ± 0.2 19 ± 0.3 0.10 ± 0.001 z Data are means ± SE (n = 3). CC = container capacity.
1308 HORTSCIENCE VOL. 52(9) SEPTEMBER 2017 Table 2. EC, pH, and nutrient content measured using the saturated paste method for growing substrates ABcann UNIMIX 1-HP (U1-HP) and ABcann UNIMIX 1 (U1). 2– - ECz Nitrate N P K Ca Mg SO4 Na Cl Zn Mn Cu Fe B Mo Growing substrate (mS·cm–1)pHz (mg·L–1) U1-HP 1.8 ± 0.07 6.30 ± 0.01 5 9.2 338.1 <1 2.7 31.2 104.5 413 <0.01 <0.01 <0.01 0.12 0.09 <0.01 U1 2.3 ± 0.12 6.28 ± 0.01 8 10.4 431.2 2.3 5.3 41.3 136.3 724 <0.01 0.01 <0.01 0.84 0.13 <0.01 z Data are means ± SE (n = 3). 2– - EC = electrical conductivity; N = nitrogen; P = phosphorus; K = potassium; Ca = calcium; Mg = magnesium; SO4 = sulfate; Na = sodium; Cl = chloride; Zn = zinc; Mn = manganese; Cu = cupper; Fe = iron; B = boron; Mo = molybdenum.
rate linearly at 13 DAT and quadratically at 19 DAT, and leaf number responded to fertilizer rate quadratically at 13 and 19 DAT. At 19 DAT, maximum leaf number was 42, achieved at a rate that supplied 420 mg N/L and maximum growth index was 51 at a rate that supplied 477 mg N/L. Treatment effects carried forward into the flowering stage in which branch number responded quadratically to vegetative-stage fertilizer rate (maximum of 17.6 at a rate that supplied 403 mg N/L) and growth index increased linearly with increasing vegetative-stage fertilizer rate. Yield. There was no yield difference between substrates, and no substrate · fertil- izer rate effect on yield. Based on the pooled data from both substrates, yield responded to fertilizer rate quadratically with the highest yield at a rate that supplied 389 mg N/L (Fig. 2). Yield at this fertilizer rate was interpolated to be 41.6 g/plant which is 1.8 times higher than that at the lowest which supplied 117 mg N/L. The yield was posi- tively correlated with growth index (r =0.45, P < 0.001), leaf number (r =0.39,P = 0.0027), and branch number (r =0.53,P < 0.0001) measured at the end of the vegetative stage (19 Fig. 1. Response of cannabis growth attributes to organic fertilizer (4.0N–1.3P–1.7K) rate [indicated by DAT; n =58). nitrogen (N) concentration] applied during the vegetative stage. Values are means ± SE and lines are the Cannabinoids. Of the analyzed cannabi- P n n best fit regression relationships at < 0.05. For days 5 and 13, = 10; for day 19, = 20 (vegetative noids, only THC, THCA, and CBN were stage; left); for days 45 and 63 (flowering stage; right) at rates that supplied 117, 234, and 468 mg N/L, above the detection limit (0.05%). Floral n = 12; at rates that supplied 351 and 585 mg N/L, n = 11. THC concentration responded quadratically to increasing fertilizer rate, reaching a maxi- mum of 0.31% a rate supplying 418 mg N/L (<0.05%), the values were excluded from (Fig. 3). There was no fertilizer rate effect on the analysis. The residuals of the above the floral THCA concentration (mean ± SE of analyses were tested for normality and equal- 10.6% ± 0.31%) or CBN concentration ity of variance using the Shapiro–Wilk test (mean ± SE of 0.08% ± 0.018%). Cannabinoid and Bartlett’s test, respectively. concentrations also varied with yield. THC and CBN were positively correlated with Results yield, whereas THCA was not correlated with yield (Fig. 4). Growth. There were no observed signs of Substrate EC and pH. Substrate pH de- nutrient toxicity or deficiency at any fertilizer creased over time for all fertilizer rates during rate during the vegetative or flowering stage. the vegetative stage (Fig. 5), decreasing Identifying nutrient disorders based on visi- linearly or responding quadratically to in- Fig. 2. Response of cannabis yield to organic ble foliar symptoms became difficult at 6 creasing fertilizer rate. The lowest mean pH fertilizer (4.0N–1.3P–1.7K) rate [indicated by weeks of the flowering stage when all plants was 6.19 at the 351 mg N/L rate, measured at nitrogen (N) concentration] applied during the began showing signs of foliar senescence. 17 DAT. Substrate EC, measured at 5, 13, vegetative stage. Values are means ± SE. The Older leaves started to become chlorotic in and 17 DAT, increased linearly over time and curve is the best fit regression relationship with P n week 6 and eventually necrotic before har- with increasing fertilizer rate. Mean EC < 0.05 ( = 12 at rates that supplied 117, 234, vest. Substrate and substrate · fertilizer rate ranged from 0.9 to 3.9 mS·cm–1 from the and 468 mg N/L; n = 11 for rates that supplied 351 and 585 mg N/L). had no effect on leaf number, branch number, lowest to the highest fertilizer rate at 17 DAT. or growth index. During the vegetative stage, In the flowering stage, pH (measured at 47 both leaf number and growth index responded and 59 DAT) increased linearly with increas- was no significant treatment effect, then data similarly to fertilizer rate (Fig. 1). Growth ing vegetative-stage fertilizer rate with were presented as the average of all the attributes did not respond to fertilizer rate at means ranging from 6.74 to 7.16 (Fig. 6). treatments (pooled). If cannabinoid concen- 5 d after the first treatment application (DAT), No difference was observed in EC among trations were below the detection limit although growth index responded to fertilizer vegetative stage fertilizer rates during the
HORTSCIENCE VOL. 52(9) SEPTEMBER 2017 1309 flowering stage with substrate EC at 1.3 ± 0.03 organic-specific fertilizer rates rather than ranging in EC from of 1.0 to >4.2 mS·cm–1 mS·cm–1 and 1.6 ± 0.02 mS·cm–1 (mean ± SE) using conventional standards as guidelines. (Sonneveld et al., 1999). In the current study, at 47 and 59 DAT, respectively. No differ- Results from our present study showed cannabis tolerated substrate EC up to 3.0 ences in substrate EC or pH were observed a fertilizer rate supplying 389 mg N/L pro- mS·cm–1 without reduction in yield. betweenthetwotestedsubstratesinboththe vided the highest yield while increasing or In all fertilizer rates, pH decreased grad- vegetative and flowering stages. having no effect on the concentration of the ually during the vegetative stage; and the cannabinoids measured. highest yielding rates, which supplied 234, Discussion Substrate EC increased over time during 351 and 468 mg N/L, exhibited the lowest pH the vegetative stage, and the increase was values. In most organic fertilizers, nitrogen + + No visual signs of nutrient disorders were more apparent at higher fertilizer rates. Sub- exists primarily as NH4 (i.e., high NH4 -N/ – observed in this trial which suggests that the optimal yields were seen at fertilizer rates NO3 -N ratio; Gul€ et al., 2007) and can be fertilizers used had nutrient elements and that supplied 468 and 585 mg N/L under taken up by plants directly or as other forms ratios within an acceptable range. Both which substrate EC was 3.0 ± 0.13 and 3.8 ± after being converted by microorganisms in growth attributes and yield of the cannabis 0.13 mS·cm–1, respectively. These yield re- the substrate via ammonification and nitrifi- plants exhibited a typical response to varying ductions may have been caused by high cation (Shinohara et al., 2011). Reductions in fertilizer application rates. Yield increased substrate salinity. High salinity can damage pH under organic fertilization can be caused + with increasing fertilizer until reaching crops through increased yS, depressing the by NH4 nitrification and the excretion of + a maximum at a rate supplying 389 mg N/L. external water potential in the root zone. In protons by the roots after NH4 uptake Optimal organic fertilizer application rates greenhouse-grown flowering crops, salinity (Johnson et al., 2011; Silber et al., 2004). It in this experiment were higher than syn- thresholds vary dramatically among species, is possible that larger plants, those fertilized thetic fertilizer recommendations for most at rates identified as, or close to, optimal in + conventional crops (Raviv and Lieth, 2007). this study, had higher rates of NH4 uptake Organic fertilizers contain slower releasing which decreased root zone pH. There are no and less soluble forms of nitrogen and experimental data in the literature on ideal phosphorus compared with most synthetic growing substrate pH range for cannabis in fertilizers and may release only 25% to 60% soilless production system; however, infor- of their nitrogen content (Prasad et al., mation we collected from the industry and 2004). Therefore, it is important to establish gray resources (Cervantes, 2006) suggest a range of 5.8–6.8 to avoid causing nutrient disorders. In the current study, there were no visual signs of pH-induced disorder in plants within the pH ranges measured (means of 6.2 to 7.1 in the vegetative stage and 6.7 and 7.2 in the flowering stage) suggesting that these ranges are suitable for container production of organic cannabis. More research is needed to determine the optimal growing substrate pH ranges for cannabis. Around the optimal fertilizer rate, both growing substrates tested in the current study demonstrated acceptable qualities for the growth of cannabis in the vegetative stage. There were no growth or yield differences Fig. 3. Relationship between Δ9-tetrahydrocannab- observed between plants grown in the lower inol (THC) concentration in dry floral material Fig. 5. Response of substrate pH and electrical WHC (drier) substrate (U1-HP) and the of cannabis and organic fertilizer (4.0N–1.3P– conductivity to organic fertilizer (4.0N–1.3P– higher WHC (wetter) substrate (U1) with 1.7K) rate [indicated by nitrogen (N) concen- 1.7K) rate [indicated by nitrogen (N) concen- fertigation administered when substrate tration] applied during the vegetative stage. tration] applied during the vegetative stage. moisture content dropped to 30%. This in- Values are means ± SE. The curve is the best fit Data are means ± SE (n = 5 for pH at the 585 mg regression relationship with P < 0.05 (n = 3). N/L rate on day 17 and n = 10 for all other dicated that both substrates were appropriate means) and lines are the best fit regression for container production of organic cannabis. relationships with P < 0.05. The positive correlations between growth attributes in the vegetative stage and final yield may indicate that growing larger plants during the vegetative stage will increase yield. Because larger plants, those fertilized at rates around the optimal fertilizer rate, had increased THC concentration in floral mate- rial (maximized at the rate supplying 418 mg N/L) and the concentrations of other canna- binoids were unaffected, it may be concluded that to optimize the yield and total THC content, cultivation techniques to increase vegetative growth, specifically branching, should be used. Besides fertigation, other Fig. 4. Relationships between cannabinoid concen- cultural practices such as topping (Tanaka trations in dry floral material of cannabis and and Fujita, 1974) may also be used to dry floral weight. Values are means ± SE (n =15 Fig. 6. Response of substrate pH during the flower- for THCA and THC; n = 13 for CBN). Lines are ing stage to organic fertilizer (4.0N–1.3P–1.7K) increase branching. the best fit regression relationships with P < rate [indicated by nitrogen (N) concentration] The highest yielding plants, those fertil- 0.05. THCA = D9-tetrahydrocannabidiolic acid; applied during the vegetative stage. Data are ized around the optimal rate, had higher THC = Δ9-tetrahydrocannabinol; CBN = can- means ± SE (n = 8), and lines are the best fit concentrations of THC and CBN. In fact, as nabinol. regression relationships with P <0.05. yield increased, so did the concentration of
1310 HORTSCIENCE VOL. 52(9) SEPTEMBER 2017 these neutral cannabinoids. During the flow- Furthermore, larger plants (e.g., higher Leggett, T. 2006. Review of the world cannabis ering stage, THCA transcription in floral growth index, branching and leaf number) situation. Bull. Narc. 58:1–155. material slows between weeks 1 and 3 generally had higher yield and floral THC Mechoulam, R., A. Shani, H. Edery, and Y. whereas total cannabinoid concentration con- concentrations which may indicate that Grunfeld. 1970. Chemical basis of hashish tinues to increase until weeks 3 and 4, as plants should be grown as large as possible activity. Science 169:611–612. Muntendam, R., N. Happyana, T. Erkelens, F. THCA breaks down into neutral cannabi- during the vegetative stage. Bruining, and O. Kayser. 2012. Time depen- noids such as THC and CBN (Muntendam Literature Cited dent metabolomics and transcriptional analysis et al., 2012). This leads to an accumulation of of cannabinoid biosynthesis in Cannabis sativa neutral cannabinoids as plants mature Ahmed, S.A., S.A. Ross, D. Slade, M.M. Radwan, var. Bedrobinol and Bediol grown under stan- through the flowering stage. It is estimated I.A. Khan, and M.A. ElSohly. 2015Minor dardized condition and with genetic homoge- that higher concentrations of neutral canna- oxygenated cannabinoids from high neity. Intl. J. Med. Plants Res. 1:31–40. Cannabis sativa binoids, as seen in plants fertilized around the potency L. Phytochemistry Potter, D.J. 2014. A review of the cultivation and 117:194–199. optimal rate, would be observed in plants processing of cannabis (Cannabis sativa L.) for Ahmed, S.A., S.A. Ross, D. Slade, M.M. Radwan, production of prescription medicines in the which mature early. Optimal fertigation dur- F. Zulfiqar, and M.A. ElSohly. 2008. Cannabi- ing the vegetative stage may, therefore, re- UK. Drug Test. Anal. 6:31–38. noid ester constituents from high potency Potter, D.J. and P. Duncombe. 2012. The effect of Cannabis sativa duce maturation time in cannabis. Early L. Planta Med. 74:536–542. electrical lighting power and irradiance on maturation is desirable as it could decrease Amaducci, S., D. Scordia, F.H. Liu, Q. Zhang, H. indoor-grown cannabis potency and yield. J. time to harvest and result in more frequent Guo, G. Testa, and S.L. Cosentino. 2015. Key Forensic Sci. 57:618–622. crop turnover. To evaluate whether fertiga- cultivation techniques for hemp in Europe and Prasad, M., P. Simmons, and M.J. Maher. 2004. tion can, in fact, reduce maturation time, China. Ind. Crops Prod. 68:2–16. Release characteristics of organic fertilizers. further study is required with cannabinoid ArcView Market Research and New Frontier. Acta Hort. 644:163–170. 2014. The state of legal marijuana markets. Raviv, M. and J.H. Lieth. 2007. Soilless culture: analyses throughout the flowering stage. 4th ed. ArcView Mkt. Res. New Frontier, San In the current study, treatments were Theory and practice. 1st ed. Elsevier B.V., Francisco, CA. Burlington, MA. applied only in the vegetative stage whereas Aubin, M.-P., P. Seguin, A. Vanasse, G.F. Tremblay, Δ cannabinoid production occurs primarily dur- Ross, S.A. and M.A. ElSohly. 1997. CBN and 9- A.F. Mustafa, and J.-B. Charron. 2015. Industrial THC concentration ratio as an indicator of the ing flowering because of an increase in hemp response to nitrogen, phosphorus, and age of stored marijuana samples. Bull. Narc. potassium fertilization. Crop Forage Turfgrass glandular trichome development in the flower- 49:139. Mgt. 1:1–10. ing stage (Muntendam et al., 2012; Vogelmann Russo, E.B. 2007. History of cannabis and its Baxter, W.J. and G. Scheifele. 2008. Growing et al., 1988). Treatment effects carried for- preparations in saga, science, and sobriquet. industrial hemp in Ontario. Ontario Ministry ward to some final floral cannabinoid con- Chem. Biodivers. 4:1614–1648. of Agriculture, Food and Rural Affairs. Russo, E.B. 2011. Taming THC: Potential cannabis centrations; however, effects may have been Queen’s Printer for Ontario, Toronto, Canada. synergy and phytocannabinoid-terpenoid more apparent with variable fertilizer treat- Bowley, S. 1999. A hitchhiker’s guide to statistics entourage effects. Brit. J. Pharmacol. ments during the flowering stage. Further in plant biology. Any Old Subject Books, 163:1344–1364. research is needed to evaluate the effects of Guelph, Canada. Ruter, J.M. 1992. Influence of source, rate, and fertilizer rate on flowering-stage cannabis. Canada Gazette. 2016. SOR/2016-230, s.2. Access method of applicating controlled release fertil- to cannabis for medical purposes regulations. Yields in the current study were slightly izer on nutrient release and growth of ‘‘Savan- lower than industry standards and reports P.C. 2016-743 (5 Aug. 2016). Canada Gazette, Part II. 150(17) 3525. 23 Nov. 2016.
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