Subcanopy and Inter-Canopy Supplemental Light Enhances and Standardizes Yields in Medicinal Cannabis (Cannabis sativa L.)

Abstract

Light supplementation within the canopy is an effective method to improve light distribution throughout the whole plant, ensuring the inner canopies receive adequate light exposure to maximize overall growth. This approach is gaining interest among cannabis growers looking for more efficient lighting strategies to enhance their valuable production for medicinal purposes. We compared the traditional top lighting (TL) approach with two light supplementation methods: subcanopy lighting (SCL), which adds extra light to the inner canopies from below, and inter-canopy lighting (ICL), providing dedicated light at the basal and middle levels. Both SCL and ICL resulted in a more uniform light distribution throughout the plants and increased the yields of inflorescences, cannabinoids, and terpenes. The ICL treatment achieved the highest yield increases, showing a 29.95% increase in dry inflorescence yield, a 24.4% higher accumulation of THC, and a 12.5% increase in total terpene concentration. Notably, both SCL and ICL reduced the coefficients of variation, yielding more standardized products by decreasing the variability of the dry inflorescences yield, which also had more consistent chemical profiles, with reductions in variability for both THC and total terpene yields of over 50%. Although using more energy for lighting, SCL was more power-efficient for inflorescence and cannabinoid yields, while ICL was more efficient in achieving yield enhancements. In conclusion, adding supplemental light to the inner canopies enhances the profitability of medical cannabis cultivation, resulting in higher yields, improved energy efficiency, and more standardized products for research and medical purposes.

Keywords: LEDs; THC; inter-canopy; medicinal cannabis; standardization; subcanopy; terpenes.

Figure 1

(a) Diagram depicting the measurements conducted at the defined levels: apical, middle, and basal thirds. At each level, measurements were taken in multiple directions (indicated by red arrows), and the PPFD recorded in each orientation was combined and averaged to determine the average PAR for each level. (b) Distribution of PAR (PPFD, μmol·m⁻²·s⁻¹) throughout the canopy across the different treatments. Data were analyzed by 2-way repeated-measures ANOVA. Means and standard errors are represented. Statistical differences in total PAR received among treatments are noted above the bars. Different letters denote significant differences (Tukey HSD, p ≤ 0.05).

Figure 2

(a) SPAD values of youngest fully developed fan leaves. (b) Fv/Fm values of youngest fully developed fan leaves. Wide bars show the mean value of whole plant, and inner bars represent the means for each fraction. Weekly values (means and standard errors, from weeks 2 to 11, W2 to W11) are depicted. Different letters denote significant differences (Tukey HSD, p ≤ 0.05) between the mean values of whole plants.

Figure 3

Dry biomass fractions (FDW, LDW, and SDW, in grams) obtained per plant fraction and treatment. Means and standard errors are represented. Statistical differences among treatments are noted above the bars. Different letters denote significant differences (2-way ANOVA and Tukey HSD, p ≤ 0.05).

Figure 4

Cannabinoid results per treatment and plant fractions. Concentration is expressed as percent (left) and yield as grams (right). Means and standard errors are represented. Different letters denote significant differences (2-way ANOVA and Tukey HSD, p ≤ 0.05).

Figure 5

Terpene concentration per treatment and plant fractions. Means and standard errors (fraction by treatment) are represented. Statistical differences among treatments are noted above the bars. Different letters denote significant differences (2-way ANOVA and Tukey HSD, p ≤ 0.05).