Forum francophone de permaculture

The way that it works can be attributed to two substances that can be found within the Salix (Willow) species, namely, indolebutyric acid (IBA) and Salicylic acid (SA).
Indolebutyric acid (IBA) is a plant hormone that stimulates root growth. It is present in high concentrations in the growing tips of willow branches. By using the actively growing parts of a willow branch, cutting them, and soaking them in water, you can get significant quantities of IBA to leach out into the water.
Salicylic acid (SA) (which is a chemical similar to the headache medicine Aspirin) is a plant hormone which is involved in signalling a plant’s defences, it is involved in the process of “systemic acquired resistance” (SAR) – where an attack on one part of the plant induces a resistance response to pathogens (triggers the plant’s internal defences) in other parts of the plant. It can also trigger a defence response in nearby plants by converting the salicylic acid into a volatile chemical form.