In the case of medical marijuana, the cultivation of active pharmaceutical ingredients requires standardization of the quality of both the products (i.e. analysis of cannabinoids, terpenes and flavonoids) and the cultivation processes. That is why most medical cannabis cultivation technique often base on indoor growing and greenhouse systems. It allows both greater control of environmental conditions and thus greater standardization of cultivation processes.
Optimizing medical cannabis growth
The importance of optimizing systems is growing due to increasing demand and the need to improve or maintain the efficiency of cultivation systems. The final yield and the quality of the inflorescences are very variable and depend on many factors, such as: genotype, agronomic practices, exposure, plant density, environmental conditions, the impact of biotic and abiotic stresses and the length of the vegetative and generative period. For this reason, there are many differences in the yield reports of medicinal cannabis in the literature.
The key to maximizing yields, however, is always the right time to harvest based on inflorescence maturity and biomass accumulation. Identifying the optimal harvest time for each genotype can help optimize cultivation processes, as cannabis is economically resource-intensive. Another important management factor is pruning, e.g. removal of the apical meristem or branches and leaves. This modulates both plant layout and biomass allocation as well as inflorescence yields, including cannabinoids per plant and area. Removing the apical meristem changes the hormonal balance in the plant. It stimulates shoot development and thus changes the plant’s architecture, which can affect access to light and air. Researchers have noted that pruning techniques affect the uniformity of cannabinoid concentrations in the plant. That is why it is so important to check the effect of harvest time and different pruning techniques on inflorescence yield, CBD content, CBDA and total CBD concentration.
Research about pruning and harvesting
A study by researchers from Germany showed that the optimal harvest time for the high CBD genotype tested was around nine weeks of flowering. The experimental pruning techniques were successful in altering plant architecture and biomass allocation, with significantly higher inflorescence dry weight in the plants. The results showed that both pruning techniques increased the yield of cannabis plants compared to unpruned plants. However, there was no significant difference in CBD concentration between the pruned and unpruned plants. In addition, the results for internal plant variability showed a much higher total CBD concentration in the upper part of the plant and much lower in the lower part of the plant. This may indicate the advantage of the pruning technique of cutting the plants apically. Thus shifting the plant biomass from the low to medium and high fractions compared to control plants.
The researchers examined three different harvest times (early, mid, and late). In terms of harvest time, the researchers found that the mid-harvest time produced the highest CBD concentration in the plants. On the contrary, the late harvest time produced the highest yield. The early harvest time resulted in the lowest CBD concentration and yield. As the study noted, the mid-harvest time produced the highest CBD concentration in the plants. This suggests that the cannabinoids were still accumulating in the trichomes at this stage. In the later harvest times, however, the researchers found a significant increase in CBD concentration. That may indicate that some of the CBD-A had been converted to CBD through decarboxylation processes. This may have been due to the extended exposure of the plant material to oxygen and light during the later stages of growth.
Why is technique choice for cannabis cultivation so important?
Given the differences in inflorescence placement, growers need to be aware of the overall variability in CBD concentration. They should evaluate different techniques to achieve their production goals and optimize their growing systems. Future work on yield optimization should take into account the importance of inflorescence location and the influence of modulation of plant architecture. Overall, this study suggests that the timing of harvest and pruning technique can have a significant impact on the yield and CBD concentration of medicinal cannabis plants, and that careful management of these factors could be important for optimizing cannabis production.