Auxins are plant hormones that regulate growth and shape. The main natural auxin is indole-3-acetic acid (IAA), made mostly in young leaves and shoot tips and moved down the stem by polar transport. Auxin promotes cell elongation, maintains apical dominance, causes phototropism and gravitropism, and triggers adventitious and lateral root formation.
In practice
Two everyday uses for growers: - Training: topping removes the main auxin source, so side buds wake up. Bending a stem changes auxin flow, which is part of why LST evens out a canopy. - Cloning: rooting products use synthetic or related auxins, mainly indole-3-butyric acid (IBA) and sometimes NAA, as gels, powders or dips. In cannabis, IBA treatment improved rooting of cuttings in controlled trials (Caplan et al. 2018).
Auxin works in balance with cytokinin: high auxin relative to cytokinin favours roots; high cytokinin favours shoots. That ratio is the core of tissue-culture media.
Rooting products are concentrates of plant-growth regulators. Follow label rates and wear gloves.
Don't confuse with
- Cytokinin: promotes shoot and bud growth, opposing apical dominance.
- Gibberellin: drives internode elongation and stretch.
- Fertiliser: supplies nutrients; hormones are signals, not food.
