Garden Doctors: When to use rooting hormones

Jacquie B. of Sebastopol asks: I want to start taking cuttings of some of my plants. When do you use rooting hormones and how do I use them?

Plants possess hormones, and one of them is called auxin which is important when you’re trying to root cuttings. Commercially available rooting hormones are natural or synthetic versions of auxin at different concentrations. Usually, low concentrations are used for herbaceous cuttings (annuals and perennials), and high concentrations are used for woody cuttings (trees and shrubs). Commercially made hormones sometimes contain cytokinins (another plant hormone), fungicides and other chemicals.

You would use a rooting hormone with cuttings that root slowly, such as most trees and shrubs, if the propagation conditions aren’t ideal, like in a greenhouse with a misting system and heating mats. It can also be used to speed up rooting time, and some species that root without hormones can benefit from hormone application, just to speed up the process.

Rooting hormones come in two forms - powder and liquid. Powders are easier to use because they’re hard to over-apply. Liquids are either alcohol- or water-based and are stronger than powders, and this makes it easier to burn cuttings if not used correctly. If you don’t know which type is best for your cuttings, check the label or ask at your favorite nursery.

Pour a little into a cup or dish, because a little goes a long way. Throw away the unused portion. Don’t pour it back into the bottle because this can spread disease! Dip the base of the cutting into the powder or liquid, tap or shake the cutting to remove any excess. Stick the cutting into your potting mix or other growing medium, after you have poked the soil with a small stick. This prevents the hormone from being smeared off when putting it into the soil. If cuttings are very dry and no powder stays on, dip the cuttings in water first.

Applying too much rooting hormone can damage the cutting. Just as taking too much medicine doesn’t cure you any faster, overdosing on rooting hormone harms the cutting rather than helps it.

Don’t get the rooting hormone on the foliage, because this causes misshapen leaves.

The next time you visit your friend’s garden, you can say to yourself, “I’d love to take a cutting of that beautiful penstemon.” By using a little rooting hormone, you too, can have that beautiful new plant!

Must have hormones: Dahlia (Dahlia), Hibiscus (Hibiscus), Lobelia (Lobelia), Cape daisy (Osteospermum

Maybe could use hormones: Pocket petunia (Callibrachoa), Fuchsia (Fuchsia), some salvias (Salvia), Snapdragon (Antirrhinum)

Don’t need it at all: Coleus (Solenostemon or Coleus), Impatiens (Impatiens), Petunia (Petunia), Moss rose (Portulaca)

Dana Lozano and Gwen Kilchherr are garden consultants. Send your gardening questions to The Garden Doctors, at pdgardendoctor@gmail.com. The Garden Doctors can answer questions only through their column, which appears twice a month in the newspaper and online at pressdemocrat.com.