Does Stress Increase THC or Terpenes?

Because cannabinoids and terpenes can contribute to plant defence, it is reasonable to ask whether environmental stress can increase their production. Growers have tried water restriction, higher EC, cold nights, additional light, nutrient restriction, heat, UV and physical damage. These interventions do not produce one consistent response.

Stress can increase some cannabinoid or terpene concentrations under particular conditions, but it can also decrease them or reduce flower biomass. A higher concentration does not necessarily mean greater total production. The practical question is whether an intervention produces a useful response while preserving photosynthesis, roots and flower development.

Stress is not the same as crop steering

A plant experiences stress when environmental conditions challenge its physiological functioning. Limited water, high root-zone salinity, excessive temperature or light, nutrient limitation and biological attack can all contribute.

Professional growers manipulate many of these variables to influence crop development, but a steering intervention is not necessarily intended to damage the crop. In tomato cultivation, for example, growers monitor the relationship between vegetative growth in leaves, stems and roots and generative growth in flowers and fruit. Excessive investment in either direction can reduce productive capacity over the season.

Wageningen University & Research guidance describes plant balance in this horticultural context: a strongly vegetative crop may carry too little fruit, while an excessively generative crop may lack enough leaf area and a sufficiently strong growing point to sustain production. Irrigation, EC, temperature, humidity, leaf removal and fruit load can influence that balance. This is professional greenhouse context, not direct evidence that tomato steering prescriptions produce the same response in Cannabis.

What steering looks like in professional horticulture

From my own work in professional horticulture, I have seen growers use changes in substrate dryback, irrigation timing, root-zone EC, temperature strategy, crop load and leaf area to give a crop a small vegetative or generative push.

Growers may informally describe this as “teasing” or “stressing” the plant, but the crop is not supposed to collapse. The aim is to observe its direction and correct an imbalance before a large swing develops.

Professional substrate guidance describes lower water content, larger drybacks and higher substrate EC as possible generative steering tools, while higher water content, more frequent irrigation and lower EC can encourage a more vegetative response. These are contextual principles, not universal Cannabis settings. Water content and EC need to be interpreted together, in relation to substrate, climate, crop stage and the actual plant response.

Mild challenge and damaging stress are different things

A relatively small environmental challenge may trigger acclimation without substantially reducing growth. A stronger challenge may change architecture or metabolism but can also begin to reduce productive capacity. The transition depends on the treatment and plant; a useful intermediate response cannot be assumed in every case.

This helps explain why the term drought stress can be misleading. A modest substrate dryback and severe wilting may both be described as drought, although their physiological consequences differ substantially.

Why would stress change THC or terpenes?

Cannabinoids and terpenes are part of Cannabis specialised metabolism. Cannabinoids can contribute to defence against herbivores, while terpenes participate in defence and ecological signalling across plant species. Environmental signals can alter their production, although the specific ecological roles require crop- and compound-specific evidence.

The compounds still require photosynthetically fixed carbon, energy, enzymes, functioning glandular trichomes, water and mineral nutrition. A treatment can stimulate defence signalling while reducing the resources available to produce flowers and metabolites. Both responses need to be considered.

Drought responses depend on timing and recovery

Dimopoulos and colleagues (2025) investigated short-term water deficit and abscisic acid during early flower development, followed by recovery until harvest. During the water-deficit treatment, cannabinoid concentrations decreased while sesquiterpenes increased. At harvest after recovery, cannabinoids were no longer suppressed, CBGA was higher and monoterpenes had increased. The reported treatment did not reduce final biomass.

A separate late-flowering study by Dimopoulos and colleagues used ‘Hindu Kush’ and examined the glandular-trichome proteome alongside floral metabolites. Water deficit increased CBGA, but proteins associated with cannabinoid and terpenoid biosynthesis either decreased in abundance or did not change. The authors proposed changes in resource allocation and stress signalling rather than a simple upregulation of the pathway's proteins.

These findings distinguish treatment effects from mechanisms proposed to explain them. They also show why responses measured during water deficit cannot be assumed to persist unchanged after recovery or apply at another developmental stage.

Controlled treatments are not the same as repeated severe wilting

A short reduction in water availability followed by recovery is different from repeatedly allowing a crop to wilt severely. The absence of a biomass penalty in one experiment does not establish a generally safe drought prescription.

For a treatment to be useful in production, the desired response needs to be evaluated alongside root condition, water uptake, canopy function and flower yield. The range within which this is possible can differ between genotypes and growing systems.

Concentration is not production

Consider a hypothetical comparison:

• Plant A produces 100 g of flower at 20% cannabinoids, equivalent to 20 g of cannabinoids.
• Plant B produces 70 g of flower at 22% cannabinoids, equivalent to 15.4 g.

Plant B has the higher concentration but the lower total cannabinoid yield. These numbers illustrate the calculation; they are not results of a particular stress experiment.

An increase in percentage alone therefore does not establish a better production strategy. Concentration per gram, total flower biomass and total cannabinoid or terpene yield per plant or square metre answer different questions.

High EC can change architecture without improving cannabinoid concentration

Higher salinity makes water uptake more difficult through its osmotic effect. Allred, Fatzinger and Bugbee (2025) tested this in the Cannabis cultivars ‘Trump’ and ‘Cherry’ grown in stone wool. The applied nutrient solutions had EC values of 4 or 8 mS/cm; a third treatment used 8 mS/cm during the first four weeks of short days and 4 mS/cm during the remaining four weeks.

These values describe the supplied nutrient solutions, not identical, constant EC values measured throughout the root zone. The researchers measured leachate separately. Feed EC, leachate EC and measurements within a substrate should not be treated as interchangeable.

The high and hybrid treatments reduced plant height by about 15%. In ‘Cherry’, flower yield declined by approximately 20% in both treatments. In ‘Trump’, a roughly 20% reduction was significant in the hybrid treatment, while the reduction under continuously high EC was not statistically significant. Cannabinoid concentrations did not differ significantly among treatments in either cultivar.

The experiment changed plant architecture without demonstrating a cannabinoid-concentration benefit. The cultivar differences matter, as do the controlled conditions: CO₂ was elevated to 1,200 ppm. Cannabinoid measurements had two subsamples per treatment and cultivar, which also limits how broadly a nonsignificant result should be interpreted.

Higher EC can be a steering tool in professional horticulture, but its effect depends on water availability, radiation, crop demand and irrigation management. These experimental feed values are not recommended Cannabis targets.

Nutrient restriction and excess both require careful interpretation

Nutrient restriction can alter cannabinoid concentrations while also reducing biomass. If a lower nutrient input maintains approximately the same total cannabinoid yield, that may be useful for nutrient-use efficiency. It is a different outcome from an increase in total cannabinoid production.

Adding more fertiliser does not necessarily improve the result either. Hershkowitz, Westmoreland and Bugbee (2025) examined phosphorus inputs of 15–90 mg/L alongside nutrient-solution EC treatments of 2 and 4 mS/cm in closed-system hydroponics. Higher inputs increased nutrient accumulation without significantly improving yield or quality in the tested system.

Those results do not establish a universal phosphorus or EC target. They show that additional input beyond the requirements met in that experiment did not produce the assumed production benefit.

Additional usable light can increase biomass and metabolite yield

Increasing specialised-metabolite yield does not always require deliberately imposing stress. Sae-Tang and colleagues (2024) grew ‘Critical CBD’ under broad-band white LEDs at 600, 800 and 1,000 µmol m⁻² s⁻¹ PPFD during eight weeks of the generative phase, with a 12-hour photoperiod.

Within that experiment, increasing PPFD increased inflorescence dry mass, cannabinoid and terpenoid concentrations, and total specialised-metabolite yield. Higher inflorescence mass was mainly associated with greater total dry-matter production, and leaf photosynthesis was higher at higher growth PPFD.

This differs from raising a concentration while suppressing biomass. It demonstrates a response in one cultivar and controlled system, not a universal instruction to raise light intensity in every crop.

Useful light can become excessive relative to plant capacity

The response to irradiance depends on water supply, CO₂, temperature, root function and nutrition. If another factor limits the use of incoming energy, additional light can exceed the plant's capacity rather than improve production.

A PPFD that is productive in one system may therefore be excessive in another. The relevant question is whether the whole crop can use the input under its current conditions.

Genetics influences the operating range

Cultivars exposed to the same dryback, EC or temperature can differ in stomatal responses, growth and metabolite profiles. A change that has little effect on one cultivar may reduce flower mass in another.

This is why crop steering requires repeated observation of a particular cultivar in a particular environment. A fixed instruction such as raising EC in a specified flowering week to increase THC overlooks the actual response of the plants being grown.

Evaluate the plant response, not only the input

A dryback percentage, EC value or VPD target is not sufficient evidence that an intervention is useful. Track changes in internode growth, water use, leaf area, root condition and flower development, together with signs that canopy function is being maintained.

Consider whether the crop has moved towards the intended balance or whether growth and water uptake have begun to deteriorate. Visible appearance and water use provide useful practical observations, but they are not direct measurements of photosynthetic rate.

Metabolite production is part of the whole production system

Growth, reproduction, maintenance and defence all depend on the plant's resources. Producing specialised metabolites is part of that system rather than a process that can be optimised independently of roots, leaves and biomass.

This does not mean growth and defence always compete directly. Additional usable light can support both, as the light experiment illustrates. When resources become limiting, however, changes in specialised metabolism need to be evaluated alongside primary production.

What about trichomes?

Cannabinoids and much of the terpene fraction are produced in glandular trichomes. Their final contribution depends on density, maturity, secretory-cell activity, enzyme expression, precursor availability and genotype.

A treatment could alter trichome density while reducing flower biomass, or change cannabinoid composition without visibly changing trichome numbers. Visible resin coverage therefore cannot establish total metabolite production.

Should growers deliberately stress Cannabis?

I would distinguish deliberate crop management from seeking damage as a route to higher potency. Changing irrigation timing, EC, PPFD, temperature, pruning or canopy structure already influences plant development. The useful question is whether the intervention moves the crop towards a defined objective without an unacceptable loss of productive capacity.

A controlled response can be useful, but neither an obvious stress symptom nor a higher laboratory percentage is enough to demonstrate success. The outcome needs to include plant function, flower yield and the total amount of the compounds of interest.

The lesson from professional growers

The principle I would transfer from professional horticulture is to observe small changes and correct an emerging imbalance before it becomes severe. This is practical experience and a management approach, not evidence that every greenhouse technique transfers directly to Cannabis.

A stable crop can be adjusted while continuing to intercept light, take up water, maintain roots and develop flowers. The purpose of the adjustment should be explicit, and the observed response should determine whether to continue or stop.

Choosing a useful intervention

Before imposing a treatment, identify the response being sought and how it will be assessed. A modest dryback might be useful under some conditions, higher EC may change architecture, and additional light may improve both biomass and chemistry where the crop can use it. In other circumstances, reducing an excessive input is the better decision.

The aim is not maximum stress or the highest possible concentration in isolation. It is a measured production outcome that accounts for plant condition, flower biomass, metabolite concentration and total yield.

References

Dimopoulos, N., Purdy, S.J., Liu, L., Halimi, R.A., Barkla, B.J. & Kretzschmar, T. (2025). Regulation of secondary metabolism in Cannabis sativa L. by abscisic acid and water deficit during early flower development and after recovery. Plant Stress, 18, 101074. https://doi.org/10.1016/j.stress.2025.101074.

Dimopoulos, N. et al. (2025). Regulation of secondary metabolism in Cannabis sativa glandular trichomes by abscisic acid and water deficit stress during late flowering development. Plant Stress, 15, 100799. https://doi.org/10.1016/j.stress.2025.100799.

Allred, J., Fatzinger, B. & Bugbee, B. (2025). Crop steering through osmotic stress can reduce height but reduced yield in medical Cannabis. Journal of Cannabis Research, 7, 92. https://doi.org/10.1186/s42238-025-00351-2.

Sae-Tang, W. et al. (2024). High light intensity improves yield of specialized metabolites in medicinal cannabis (Cannabis sativa L.), resulting from both higher inflorescence mass and concentrations of metabolites. Journal of Applied Research on Medicinal and Aromatic Plants, 43, 100583. https://doi.org/10.1016/j.jarmap.2024.100583.

Hershkowitz, J.A., Westmoreland, F.M. & Bugbee, B. (2025). Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science, 16, 1433985. https://doi.org/10.3389/fpls.2025.1433985.

Wageningen University & Research. Plant Balance. Professional greenhouse crop-management guidance. https://edepot.wur.nl/156934.

Grodan. Steering crops in high-tech controlled environment agriculture. Part 2. Professional substrate-management guidance. Grodan white paper.