It sometimes surprises people that it gets cold enough in the Phoenix desert to freeze. Nighttime temperatures that get down to freezing and below will damage some trees and plants if you don't take precautions against frost.
Low temperatures that can harm frost-sensitive plants may begin in late November and continue through February and beyond. There might be between seven and ten nights where the temperatures are below freezing and plants might be damaged.
Ten Things to Know About Frost and Your Desert Garden
- Know which plants in your garden are sensitive to frost. Some of the most common frost-sensitive plants that people in the Phoenix area plant in their yards are Bougainvillea, Hibiscus, Natal Plum, Cape Honeysuckle and the Red Bird of Paradise. Many people in the Valley of the Sun have citrus trees, and they can be frost sensitive. Non-native cactus plants may also be at risk. If your plants are new or actively growing they probably need frost-protection.
- If you have frost-sensitive plants in your yard, plant them in the most favorable places to minimize winter frost. The south or west sides of the property, near the pool, close to block walls, rocks or concrete that retain heat from the daytime sun, or under roof overhangs, eaves or patio extensions (but not in full shade). You get the idea. Plant them in a place where there's likely to be more protection and more warmth.
- When you listen to the weather report on the local news, remember that the weather station where the official temperature is taken is in central Phoenix. That might be very different from the weather you get at your house. Different parts of the Phoenix metro area may be colder, depending on the elevation, the amount of concrete in the area, etc. You should probably get a thermometer and compare your actual temperature to the local Phoenix forecasts. That way, if you know that your reading is always about four degrees colder, you'll be prepared for frost even if they say it will be a low of 35°F in Phoenix.
- To protect plants and trees from frost damage, they need to be covered. Use sheets, light blankets or burlap. Hardware stores actually sell large sheets of light, porous cloth for this purpose. We keep several of them on hand. If you need to buy them, don't wait until the first frost, because they sell out quickly. Don't have extra sheets and new ones are too expensive? Try buying sheets at thrift stores.
- Do not use plastic to cover your plants. That traps the moisture under the tarp and damages the plant. Of course, in theory when covering any plant or tree you are supposed to do it such that the cloth is not touching the leaves or branches. Don't use heavy cloth or blankets; when they soak up the moisture they can become very heavy and damage the plant.
- In theory, the best way to cover a plant or tree is to make sure that your cover touches the ground. This helps to retain all the warmth under the cloth.
- Citrus trees that have not yet reached maturity, and especially lime and lemon trees, need frost protection. It can be very difficult to cover large trees, but either do the best you can, or take your chances. Unless it is a severe frost, a mature citrus tree will most likely come back from frost exposure the following spring.
- Keep watering your plants evenly during the winter. Wet soil absorbs heat during the day. In the winter always water your plants and trees in the morning. That way the leaves will be dry by the time it starts to get cold at night. As always, don't overwater.
- Don't remove plant and tree frost covers if it is still dark, and preferably not until late in the morning the next day. Some of the coldest temperatures are just after sunrise.
- If frost gets to your plant, don't remove the damaged parts. They might not look great for a couple of months, but those dead branches and leaves provide protection for the part of the plant that is still alive. You can prune frost-damaged plants in the spring.
When dealing with cold, freezing nights, it is better to do something for your plants than nothing. Use paper bags or boxes on sensitive ground covers or flowers. Drape a sheet over as much of a tree or plant as you can. When the winter is over, and you are able to trim the dead branch tips and leaves, you might very well still have a viable plant. Desert gardeners will also need to know when to prune and when to leave the plants alone.
Which are the frost sensitive plants in your yard? If you know the names of the plants, you can look them up at Desert-Tropicals.com.