There are several hormones that are used to assist root formation on cuttings. The most common is Indole butyric acid (IBA) although Naphthalene acetic acid (NAA) is also used, sometimes in combination with IBA.
|Applying a talc-based hormone powder
to the base of a cutting.
The products are usually available as powders in several strengths (softwood, medium wood and hardwood), but they can also be available as a gel or in liquid form. The 'medium' strength is recommended for most applications.
To use these chemicals, the lower centimetre or so of the cutting is dipped into the powder, liquid or gel before setting the cutting into the propagating mix. It's usually a good idea to pour out a small amount of the hormone into a small container - sufficient for the number or cuttings to be treated in the current session - to prevent possible contamination of the chemical remaining in the original container.
Do they work? Most experienced growers would say "yes". The use of hormones often results in a stronger root system and may also produce earlier root formation. Many would also claim that the liquid formulations are superior to the other types but hard data is not readily obtained.
One fact to keep in mind whatever the formulation is that the hormones have a limited shelf life and should be kept in a cool, dark place when not being used (eg. a refrigerator).