Chapter 20

Vegetative Plant Propagation

Rooting Hormones

Auxins are natural plant hormones that encourage root formation on cuttings and are available from natural and synthetic sources. In practice, auxins are commonly referred to as rooting hormones. Most cuttings are treated with synthetic hormones that are available in powder and liquid form, and some preparations may contain chemical fungicides (e.g., Captan). Synthetic hormones can be purchased ready to use or can be mixed by growers to specific concentrations using ingredients purchased from horticultural suppliers. Indole-3-butyric acid (IBA) and naphthaleneacidic acid (NAA) are the most widely used synthetic auxins. Often, mixtures of IBA and NAA are more effective than either component alone.

Powdered Products

Many growers prefer powders because several commercial products of varying strengths are available, they are easy to use, and large quantities of cuttings can be treated quickly. Powder must be applied uniformly to all cuttings; variable amounts of rooting powder adhere to the base of a cutting, which can affect rooting results. The following precautions and special techniques are necessary when using powders:

Liquid Products

Liquid products are formulated with alcohol and often must be diluted with great care to create the desired strength. Some of the advantages of using solutions are the availability of a wide range of commercial preparations, specific concentrations can be formulated at the nursery, and they can be stored for longer periods under the right conditions. Some growers believe that liquid solutions are more accurate than powders regarding the amount of rooting hormone entering the stem tissue.

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