High Light Intensities Can Be Used to Grow Healthy and Robust Cannabis Plants During the Vegetative Stage of Indoor Production

Abstract

Although the vegetative stage of indoor cannabis production can be relatively short in duration, there is a high energy demand due to higher light intensities (LI) than the clonal propagation stage and longer photoperiods than the flowering stage (i.e., 16 – 24 hours vs. 12 hours). While electric lighting is a major component of both energy consumption and overall production costs, there is a lack of scientific information to guide cultivators in selecting a LI that corresponds to their vegetative stage production strategies. To determine the vegetative plant responses to LI, clonal plants of ‘Gelato’ were grown for 21 days with canopy-level photosynthetic photon flux densities (PPFD) ranging between 135 and 1430 µmol·m-2·s-1 on a 16-hour photoperiod (i.e., daily light integrals of ≈ 8 to 80 mol·m-2·d-1). Plant height and growth index responded quadratically; the number of nodes, stem thickness, and aboveground dry weight increased asymptotically; and internode length and water content of aboveground tissues decreased linearly with increasing LI. Foliar attributes had varying responses to LI. Chlorophyll content index increased asymptotically, leaf size decreased linearly and specific leaf weight increased linearly with increasing LI. Generally, PPFD levels of ≈ 900 µmol·m-2·s-1 produced compact, robust plants that are commercially relevant, while PPFD levels of ≈ 600 µmol·m-2·s-1 promoted plant morphology with more open architecture – to increase airflow and reduce the potential foliar pests in compact (i.e., indica-dominant) genotypes.

Supplemental greenhouse lighting increased the water use efficiency, crop growth, and cutting production in Cannabis sativa

“…Despite growth increments in the vegetative stage of cannabis under high light, the light-to-biomass conversions in Moher et al. (2021) were lower than in our study.…”

“…Within the realm of cannabis cultivation, this study, as well as prior investigations employing exclusive LED lighting sources ( Moher et al., 2021 ; Rodriguez-Morrison et al., 2021 ), provides compelling evidence to classify cannabis among the most elevated lighting requiring crops. For comparison, optimal lettuce production is associated with a maximum of 17 mol m -2 d -1 for marketable leaf growth, with higher light levels potentially leading to increased biomass but also an elevated risk of leaf tip burn ( Both, 2002 ).…”

“…(2021) were lower than in our study. For instance, the biomass yield in the Moher et al. (2021) study was 246 g m -2 with 52 mol m -2 d -1 , and it increased to 271 g m -2 with 82 mol m -2 d -1 .…”

“…In corn breeding, supplemental greenhouse lighting is recommended to reach up to 750 µmol m -2 s -1 or ≥38 mol m -2 d -1 , depending on the photoperiod, while corn research in chamber conditions employs as much as 1000 µmol m -2 s -1 or 58 mol m -2 d -1 ( Eddy and Hahn, 2010 ). Remarkably, indoor farming studies have shown that cannabis crops can utilize 82 mol m -2 d -1 for shoot growth ( Moher et al., 2021 ) and 78 mol m -2 d -1 for flower production ( Rodriguez-Morrison et al., 2021 ).…”

“…For instance, cannabis flower yield exhibited a linear increase in response to increasing DLI levels, up to 78 mol m -2 d -1 , which represented the highest DLI investigated under short-day conditions, 12 h ( Rodriguez-Morrison et al., 2021 ). Moreover, when subjected to long day durations, 16 h, the shoot biomass demonstrated a similar positive trend and increased even with 82 mol m -2 d -1 ( Moher et al., 2021 ). However, it is essential to acknowledge that the dynamics of light within the context of greenhouse production can deviate substantially from those observed in sole-source LED facilities, and those changes may strongly affect plant physiological and crop efficiencies.…”