The coldest time of the year in this area is generally from mid-December through January. Have your damage control plan ready because frost conditions may occur any time from now through mid-March. That means a handy supply of old bed sheets, light blankets, newspapers, or commercial frost cloth for covering cold-sensitive plants.
Cold soil, long nights, and occasional freezing air temperatures make it difficult for perennial transplants to adapt this time of year. It is therefore recommended to hold off on planting, pruning, or fertilizing perennials. Also be aware that any plants in containers are more vulnerable to low temperatures than are those in the ground.
Hardy annual plants such as Sweet Alyssum, Pansy, Petunia, Viola, Snapdragons, Stock, Calendula and Dianthus can still be set out this month. However, it is not advised to plant seed now because most annual seed does not germinate in cool soil. Check before watering your annuals to be sure the top l inch of soil is dry.
When freezing temperatures become frequent, keep cactus and succulents dry, whether in containers or the ground. These plants are more susceptible to freeze damage when taking up water. Also do not fertilize cactus during December.
To protect columnar cactus, invert a Styrofoam cup over the growing tip for the next couple of months.
When commercially available, bare-root roses can be planted during the next month. Do not fertilize roses in December. Prune them only to remove spent blossoms and dead canes that remain on the plants. Water roses deeply every seven to10 days, in the absence of winter rains.
Cold hardy shrubs can also be planted this month; however, do not prune nor fertilize them now. For the first year in the ground after planting, do not prune shrubs. Adding a layer of protective mulch to these plants is desirable, but do not allow it to lie against the bark.
Deciduous and bare-root trees can be planted in December, but do not plant cold-sensitive trees or palms. It is recommended to not feed nor prune trees this month. However, water is now very important in the life of the tree, whether by winter rainfall or deep irrigation.
During cool weather aphids can appear, especially on vegetable and herb plants. First, try spraying them off with the garden hose. If that does not get rid of the insects try the following. Add 4 to 5 cloves of garlic to a quart of water in the blender. Process to a light slurry and use to spray infested plants.
Leave time this month to peruse the early flower-filled garden catalogs that start arriving in the mail … and to prepare for the festive atmosphere of the coming holidays!
Mary Kidnocker is a University of Arizona Master Gardener who lives in the Green Valley area. Her articles are featured weekly.