What Is Rooting Hormone?
Rooting hormone is a tool you can use to encourage a cutting of a plant's stem and foliage to start producing root cells. Plants do this naturally, and while some plants can root themselves easily when you just stick them in a glass of water, others need a little chemical encouragement.
The main ingredient in rooting hormone is auxin, a growth-regulating hormone that occurs naturally in plants. It stimulates the new cells of a plant's stem to elongate into root cells — but what the hormone is actually doing is suppressing the plant's ability to differentiate between root, stem and leaf cells. When exposed to auxin, the plant's fresh cells essentially "forget" they're able to make a variety of different types of cells, and just start replicating root cells, which are the most basic type. Thanks to the natural auxin found in plants, this can occur even without help, but a little auxin can speed up the process.
Are There Different Kinds of Rooting Hormone?
Auxin-based rooting hormone comes in powder, liquid and gel form, and in different concentrations. Some gardeners prefer powdered or spray rooting hormones because they are less likely to be contaminated by a diseased plant than a liquid product.
Larger plants generally need a higher concentration of the rooting hormone than smaller, herbaceous plants. Semi-hardwood and hardwood plants require 10-20 times the product you would use on something like a small succulent.
How Do You Use Rooting Hormone?
Although the product label will have general directions about how to use it, and in what concentration, it's a good idea to research directions for the specific type of plant you're trying to propagate before using rooting hormone.
In general, to propagate a plant with rooting hormone, first clip a piece from the parent plant with a clean knife or scissors — stem cuttings are likely to work best, but the hormone can also work on roots and leaves. Dip the cut surface of the clipping in the rooting hormone and then place it in potting medium, making sure to keep the medium damp, but not overwatered. Rooting hormone should never be used when propagating in water, since it will wash directly off the cutting.
Rooting can take a couple weeks to a couple months to work, but the roots will be more robust than if you used no auxin-boosting product. It's important to use the correct amount of rooting hormone, however, as too heavy a dosage can dehydrate or burn the plant's stems, change the plant's color or keep it from flowering.
Rooting hormone is available for purchase at most big box and smaller garden store retailers.