Fine-Tuning Irrigation: The effects of phase-specific drought stress on Cannabis sativa L. architecture, yield, and cannabinoid content.

Dominique Van Gruisen
Aug 7, 2025
4 min read

Updated: Aug 8, 2025

A whitepaper by Innexo BV – Research by Ramon van Esch

Summary

Optimizing irrigation strategies is key to balancing yield, plant architecture, and cannabinoid content in medicinal cannabis cultivation. This whitepaper summarizes the findings of a trial conducted at Innexo BV that investigated how drought stress applied during two specific flowering phases—the transition phase and the generative phase—affects plant height, flower yield, and the chemical composition of Cannabis sativa L. Results show that while phase-specific drought stress can help steer plant growth and improve product quality, it also introduces trade-offs that growers must consider carefully.

Research Design

This study was conducted in a climate-controlled glasshouse with LEDs using rooted cuttings of two cannabis cultivars, 'Skunk' and 'Strawberry', grown in coco coir under controlled fertigation. The no-veg method was applied, meaning rooted clones were transferred straight to the greenhouse with a 12-12h light-dark cycle, omitting the vegetative phase. The research consisted of two trials: on in the transition phase, first 3 weeks of the flowering phase, and one in the generative phase, the last 4 weeks of the generative phase.

*Figure 1: Treatments during the transition phase experiment.*

In the transition phase experiment, following transplanting, substrate was not irrigated for 7 days. Then treatments were imposed by delaying irrigating to field capacity for 1, 3, 7, or 12 days, control, mild moderate, and severe treatments, respectively (Figure 1). Thereby imposing low substrate water content for a variable period. It was hypothesized that this would reduce the flowering stretch and increase yield. In the generative phase experiment, overnight dry backs of 10, 15, 20, or 30% were used to create controlled drought conditions over the final four weeks of flowering. It was hypothesized that this would not affect morphology, but increase flower yield and cannabinoid and terpene content. Flower samples were categorized by location on the plant (top, side, bottom, rest) to assess chemical variability. Measurements included plant height, dry biomass, leaf area, flower yield, and inflorescence chemical composition using near-infrared spectroscopy. Data were analyzed using two-way ANOVA to determine the effects of treatment and cultivar.

Key Findings

Transition Phase (early flowering)

Drought stress reduced plant height and internode length in one cultivar (Figure 2). However, this was accompanied by a significant reduction in total biomass and flower yield under severe drought (Figure 3). Terpene content increased in one cultivar, particularly in the one most affected in terms of biomass.

*Figure 2: Plant height of two Cannabis sativa cultivars ‘Strawberry’ and ‘Skunk’ under different drought treatments in the transition phase. Error bars represent mean ± SD (n = 10).*

*Figure 3: Flower dry weight of two Cannabis sativa cultivars ‘Strawberry’ and ‘Skunk’ under different drought treatments in the transition phase. Error bars represent mean ± SEM (n = 10).*

Furthermore, strong variation in THC and terpene levels was observed depending on the sampling location of the inflorescence: flowers at the top of the plant had up to 4% higher THC content than flowers at the bottom - highlighting the importance of consistent sampling protocols.

Generative Phase (late flowering)

Drought had no observable impact on plant height or morphology in either cultivar. However, flower yield was reduced under moderate drought stress, while severe drought did not have the same effect, suggesting a non-linear stress response (Figure 4).

*Figure 4: Flower dry weight of two Cannabis sativa cultivars ‘Strawberry’ and ‘Skunk’ under different drought treatments in the generative phase. Error bars represent mean ± SEM (n = 10).*

A trend of increasing THC content with drought intensity was observed, although terpene content was more variable and showed cultivar-specific responses (Figure 5+6).

Figure 5: Tetrahydrocannabinol (THC) content of dried inflorescences at harvest of Cannabis sativa cultivars ‘Strawberry’ and ‘Skunk’ under different drought treatments in the generative phase. Error bars represent mean ± SEM

Figure 6: Total terpene content of dried inflorescences at harvest of Cannabis sativa cultivars ‘Strawberry’ and ‘Skunk’ under different drought treatments in the generative phase. Error bars represent mean ± SEM (n = 3).

Implications for Growers

Phase-specific drought stress can be a useful crop steering tool, but it requires careful calibration and cultivar-specific adjustments. Drought in the transition phase may reduce vertical stretch, aiding in crop uniformity and spatial efficiency, but it may also reduce biomass and yield. Generative phase drought may increase THC content without altering plant structure, but with a risk of yield loss under moderate stress. An additional finding is that consistency in flower sampling is crucial, as chemical composition varied significantly by plant location.

Cultivar-Specific Response

Genotype plays a decisive role in drought response. The compact cultivar ‘Skunk’ showed limited morphological change under drought, while the taller ‘Strawberry’ cultivar responded more clearly in both height reduction and terpene accumulation. These results support the use of cultivar-specific irrigation strategies to optimize both plant structure and chemical composition, however, should be tested to assess potential

Conclusion

Drought stress, when applied in a controlled and timely manner, offers a promising tool for crop steering, reducing the flowering stretch, and the enhancement of specific plant metabolites. However, these benefits might come at the cost of reduced yield, and the effects differ significantly between cultivars. These findings emphasize the need for cultivar-specific strategies and reinforce the importance of precision irrigation and standardized sampling in medicinal cannabis cultivation.

More Information

This whitepaper is based on the MSc internship research of Ramon van Esch, conducted at Innexo BV. To receive the full report contact: dewi.delange@innexo.nl