Frost season in Phoenix typically runs mid-November through February. The frequency and intensity of frost varies in both rural and metro areas for a number of reasons including elevation and population density. Our cooler weather provides us with the opportunity to conserve one of the desert’s most precious resources; water.
From roughly Thanksgiving to the end of February, most desert and desert adapted plants do not require water. You can choose to reduce your watering schedule to just a day or two a week or even turn the controller off completely! If you choose to turn your controller off completely, it’s important to continually monitor your lawn for signs of stress and provide water when necessary Once night time temperatures return to the upper 70s, you will want to start watering again. Since most plants go dormant during this time of year and you can find the emitter a little easier than when plants are blooming, late winter/early spring is an excellent time to check your irrigation system for any faults or malfunctions. Turn your controller on one zone at a time and verify that each irrigation head is functioning properly.
Protect your Backflow
When temperatures dip below 32 degrees Fahrenheit your backflow is at risk for damage from freezing water that sits in the unit. Usually, the easiest way to protect your backflow preventer is to cover it with a towel or blanket, as pictured, on the nights that temperatures are projected to drop below freezing. You can also choose to drain the water from your backflow if you are concerned about prolonged freezing temperatures or plan to be gone for several nights. For more information on how to winterize your home sprinkler system including your backflow, please visit the Colorado State University Extension website.
Frost Protection for your Plants
Cover plants susceptible to frost-damage with cloth towels, blankets, sheets or paper/cardboard boxes to insulate them. Plastic is not recommended for plant cover. Drape the paper or cloth all the way to the ground to help trap heat radiating from the ground under the cover. A nursery can help you identify material made specifically for covering plants. Remove the cover after sunrise each morning or when the temperature reaches 35 degrees.
Plants not native to the Southwest are most at risk for frost damage. These plants include Bougainvillea, Lantana, Winter Annuals and others. For cacti such as Mexican Fencepost, covering the tops of the posts with an old t-shirt, foam cup or wash cloth can help prevent frost damage. Watering plants the night before a frost can also help them stay warmer. Dehydrated plants are more susceptible to frost damage.
To Prune or Not to Prune?
If frost impacts your plant material, it is optimal to wait until the threat of frost has subsided to prune frost-damaged plants. Pruning away frost damage too early can result in additional damage to the plant if it is hit by frost again. New and un-established shrubs or ground cover plants are more susceptible to permanent damage and could be lost due to cold weather. Established plants with a sustainable root system can handle minimal pruning for aesthetic reasons throughout frost season.
When it comes to trees, some species like Ficus are particularly sensitive to frost damage. Many smaller trees may be lost all together and, unless particularly protected, significant portions of the larger trees may be severely damaged due to hard frosts. While it is hard to be patient, it is best to wait to see if new growth will come back. If you decide to prune the dead tissue, it will take years before it grows to its original size. If you decide to leave it, the green will eventually fill in, but you’ll be looking at brown dead tissue for several years.
No matter what steps you follow to prepare for cooler weather, it’s important to take proactive measures to prevent any loss of plant material, irrigation components and ultimately, your money, during the winter months.
For more information on desert landscape and plant care, check out Arizona Cooperative Extension. If you reside elsewhere in the southwest, contact your local Cooperative Extension office.