Gardening: Put your cold protection plan in place

Don’t think that winter skipped past us. The warm autumn may have lulled us into thinking temperatures will be like this all winter. However, with the average first-frost date being Nov. 15, the Santa Cruz Valley may see freezing temperatures anytime from now through early April.

Most native and desert-adapted plants are cold hardy, but also grown here are many cold-sensitive selections. For these particularly, a plan for winter protection should be ready. First, in the early day, make it a habit to check the local weather prediction for nighttime lows. Then be ready to take protective action if needed.

On the morning prior to a predicted frost, water plants thoroughly, including those in containers. The sun will have time to warm the moist soil before you cover the plants that evening. Moving containers of cold sensitive plants under a tree or patio cover may be all the protection they need.

Plant covers may include commercial frost cloth, old bed sheets, paper grocery bags, light blankets or newspapers. Do not use plastic because it transmits the cold and damages leaf surfaces.

Bottlebrush, Brazilian pepper tree, bougainvillea, lantana, cape honeysuckle, Arizona yellow bells, hibiscus, young queen palms, pygmy date palm, hardenbergia, snail vine, queen’s wreath vine, red bird-of-paradise, and many non-native cactus are cold-sensitive. Most have cold-hardy root systems, so when spring warmth arrives, they will recover quickly.

Winter annuals vary in their cold hardiness. Petunias and pansies can take cold down to 20 degrees. Begonias, geraniums, and impatiens are damaged at 32 degrees. Snapdragons, stock, and calendula fall somewhere in between. If you have a mixed planting of annuals, it may be best to cover them when temperatures fall below freezing.

Columnar cactus can be protected by inverting a Styrofoam cup over the growing tip. There is some debate about whether to leave these cups on the cactus all winter. There is thought that the cups cause sensitivity to sun on the skin when left in place a long while before removal. The suggestion here is to remove the cups every week or so, to allow for sun exposure, replacing when needed. For several years, at The Arid Garden, the cups have been left on cactus all winter with no obvious harm so far.

Cold hardiness of citrus depends on the age of the tree and the duration of cold. When temperatures drop to the critical level for just a few hours, little or no injury will occur. However, if below these levels for 10 or more hours, damage may be severe. The first two to three years after planting, any citrus should be covered when temperatures drop below freezing. Young citrus, regardless of type, will become more cold hardy as they mature.

Among citrus trees, tangerines and grapefruit can tolerate temperatures into the low 20s. Oranges can withstand temperatures in the mid-20s; lemons into the upper 20s. Most cold sensitive are limes which can suffer injury when temperatures fall below 32 degrees.

Large citrus trees may need the addition of a heat source such as a light bulb under the cover, or a string of old-fashioned 7-watt Christmas lights. In this case, be sure the frost cover fits to the ground to envelope the heat.

Temperatures will vary in Green Valley by as much as 5 to 10 degrees, depending on location. Look at where your plants are and keep in mind that cold air rushes to the low areas, down washes and arroyos. Neighborhoods east of Interstate 19, near the Santa Cruz River may have frost when the western foothills do not.

The subject of winter protection is an important one in the desert. If our temperatures dip, don’t take the chance of frost damage in your landscape... when in doubt, protect.

Mary Kidnocker is a Master Gardener who lives in Green Valley. Her columns are featured each Sunday.