In the Garden:
Southwestern Deserts
December, 2008
Regional Report

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PVC pipe vaulted over a citrus tree supports bird netting or frost cloth, depending on season.

Protect Frost-Tender Plants

Utter the word "desert" and most people think "heat." It is a surprise to some visitors that Southwestern deserts also experience freezing cold. Frost strikes as early as mid-November and as late as early April, depending on elevation and other factors. Be prepared to protect frost-tender plants such as bougainvillea, hibiscus, lantana, natal plum, yellow bells, and annual and perennial garden beds. Citrus fruit and foliage can be damaged when temperatures drop below 29 or 30 degrees F for 30 minutes or longer. The longer the cold lasts, the greater the damage.

Prepare
Study your microclimates on a regular basis. Temperatures can vary significantly within a small area. Record daily high and low temperatures in your yard from year to year, and compare with official weather reports. This information helps you gauge when protection is most likely needed. Gather materials and store in a convenient location. Use burlap, sheets or blankets, or special frost protection material.

Wrap trunks of young citrus trees. Loosely wrap multiple layers of insulating material (cardboard, newspaper, burlap, or frost cloth) from the ground up to the lowest branches. This can be left on all winter but if it gets wet, replace it.

Reduce Heat Loss
During the day, soil, hardscape surfaces, and even plants absorb heat. On cold clear nights, this heat escapes (radiates) quickly into the atmosphere. Covering plants with material that reaches all the way to the ground retains rising heat around the plant. If practical, use stakes, poles or PVC pipe as a "tent frame" to drape the material over so that it does not touch leaves, which reduces foliar damage. There should be no openings to allow heat to escape. Don't gather the material and tie it around the trunk or heat will be lost.

Drape the cover over plants as the sun is setting. (If you wait too long, the heat has already escaped.) Remove sheets, blankets, or burlap the following morning before temperatures reach 50 degrees F. Otherwise, it heats up in the "tent" and the buds break dormancy. If using frost protection material, check product specifications. Some of these fabrics are more "breathable" and can remain in place longer.

Add More Heat
Apply water to the surrounding soil. As water cools, it releases energy in the form of heat, increasing the surrounding air temperature slightly, probably no more than two degrees. Let hose or drip irrigation trickle around the base of the tree several hours before temperatures are predicted to drop and continuing until they rise. This method shouldn't be used more than several days in a row as roots rot in waterlogged soil.


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