December gardening tasks

In December, gardeners should watch for signs of approaching frost because an early or a late frost causes the most plant damage. When temperatures drop, be especially wary of clear, windless nights. Welcome rain and fog, which help protect the garden from extensive frost damage.

When frost is expected, protect tender garden plants such as bougainvillea, citrus, fuchsia and succulents by covering them. This is best done by setting stakes in the ground and draping burlap, plastic or sheets over the stakes, making sure that the covering does not touch the plant. Cardboard boxes also make handy coverings. Remove the covering when the temperature rises. If you use frost cloth (sold in garden centers), the cloth can remain in place. In areas where the temperature does not go much below freezing, protect vulnerable plants by spraying them with an anti-transpirant (commonly used on indoor Christmas trees and greens). This technique works best when employed early and reapplied in January.

- Clean up the garden by weeding, raking and storing pots, which will discourage garden pests from wintering in the garden.

- Spray horticultural oil (diluted with water to the manufacturer's specifications) on roses and fruit trees after they have dropped their leaves. Dormant sprays kill overwintering insect eggs, mites, soft-bodied pests and some scales.

- Bait or otherwise remove snails around cymbidium spikes. Once the buds have reached full size, bring cymbidiums indoors.

- Tend holiday plants brought indoors. Azaleas and cyclamen are outdoor plants that suffer inside a hot, dry house. Misting them helps them survive indoors. Unlike chrysanthemums, the azaleas and cyclamen sold for indoor use do fine when later transplanted outdoors.

- Select poinsettias (pictured) with green foliage all the way down to the soil line, which indicates active, healthy roots. Place them in a location with bright, morning daylight. Hot afternoon sunlight could fade the colored bracts. They like to be slightly moist and placed out of drafts of either hot or cold air. Poinsettias have been bred to become indoor holiday plants that last for months.

- Katherine Grace Endicott, home@sfchronicle.com

This article appeared on page M - 4 of the San Francisco Chronicle