Abscisic acid (ABA) is the plant's main drought and stress hormone. When roots dry out or leaves lose water, ABA levels rise within minutes and guard cells close stomata to cut water loss. ABA also keeps seeds dormant, slows growth under stress and helps leaves cope with cold and salinity. Despite the name, its role in abscission (leaf drop) is minor; ethylene does most of that.
In practice
ABA is why plants stop drinking and growing when the medium gets too dry or the air too harsh. With stomata shut, CO₂ uptake falls and growth stalls, even with perfect light.
It's also part of the story behind controlled late drought. Caplan et al. (2019) reported that a moderate drought stress in late flower raised cannabinoid concentration and yield per area in their trial. GenetixBay endorses mild late dry-backs where a cultivar tolerates it (Supported, house-endorsed), and notes every cultivar responds differently. Push too hard and you lose yield.
Don't confuse with
- Ethylene: the ripening and senescence gas.
- Cytokinin: a growth hormone that ABA broadly opposes.
- Wilting: the visible result of water loss, which ABA tries to prevent.
Microscopic pores, mostly on the underside of leaves, each opened and closed by two guard cells to control gas exchange and water loss.A gaseous plant hormone that regulates ripening, senescence, stress responses and, in cannabis, female flower expression; blocking it makes females produce pollen.Drying cannabis below the target water activity (under about 0.55), leaving buds brittle and harsh, with lost terpenes; rehydrating does not restore them.A cannabinoid is any compound that binds the body's cannabinoid receptors or shares the typical cannabis terpenophenolic structure; the plant-made ones are phytocannabinoids such as THCA and CBDA.Dryback is the drop in a substrate's water content between irrigations, usually expressed as a percentage of its content at full saturation.The programmed ageing and breakdown of leaves and other tissues, in which the plant recycles nutrients (especially nitrogen) from old leaves to developing flowers and seeds.A class of plant hormones made mainly in roots that promote cell division, shoot and side-bud growth, and delay leaf ageing.The evaporation of water from a plant, mainly through open stomata, which pulls water and dissolved nutrients up from the roots.
