By Tom Mcdonald
Frost is the most common type of cold weather plant injury in our area. When low temperatures combine with humidity and calm, clear nights, surfaces such as leaves and car windshields cool faster than the surrounding air – hence, frost. Young plants, those recently transplanted, plants near washes and those planted in the open are particularly vulnerable.
Frost is challenging enough but a freeze is worse. Plants especially need protection during a freeze when temperatures dip below 32 degrees and remain there for a period of time. This doesn’t happen often in our part of the Sonoran Desert, but it does happen and sometimes with little warning.
Now for the basics of protection. Since warmth at night radiates up from the earth and cold is dropping from the sky, we want to cover the plants completely with the cloth going clear to the ground to trap the warmth of the earth. Cloth is much better than plastic and frost cloth is readily available this time of year. Install the covers in the afternoon before temperatures start to drop and remove them the next day as soon as the air has warmed back up to a safe level. This will allow the soil under the plants to heat up again. An incandescent light combined with cloth can protect even the most frost-sensitive plants but use caution! Light bulbs can start fires and will burn any plant material they come in contact with.
If frost damage has already occurred and your plants have taken on that “just blowtorched” look, do not trim it off. The burnt foliage will provide some protection for the undamaged leaves underneath and help prevent further damage. It is usually safe to trim frost damage off around mid-March. Most of our desert adapted plants will rise like the proverbial Phoenix if shown a little patience. Keep those pruners in their scabbard till spring!
At Smiling Dog Ranch, we tend to only cover a few of the most sensitive specimen plants like my Myers lemon (damaged at 32 degrees). Otherwise we just hunker down, live with the damage and have a major clean up in March.
A good site to check out for a list of cold-tolerant winter blooming plants is Mountain States Wholesale Nursery (mswn.com). Click on Plant Information, then Winter Wonderful, and don’t forget to buy your plants locally!