Even the hottest of desert climates can experience frost at some point during the year. If precautions aren't taken, nighttime temperatures dropping to freezing and below can damage trees and plants. For deserts within the United States, potentially harmful low temperatures may begin as early as November and continue through February or even March.
If you take the time to prepare, your plants and trees can prevail after the lowest desert temperatures. The following tips will help protect your garden from frosty nights.
Know Your Plants
It's essential to learn which plants in your garden are easily damaged by low temperatures. Some of the most common frost-sensitive desert plants are Bougainvillea, Hibiscus, Natal Plum, Cape Honeysuckle, and the Red Bird of Paradise. Citrus trees and non-native cactus plants may also be at risk. If your plants are new or actively growing, they probably need frost-protection.
Utilize Strategic Locations
Plant frost-sensitive plants in the most favorable places to minimize the risk of damage. Some ideal spots include near the pool, south or west sides of the property, close to areas that retain heat like concrete walls, or underneath roof overhangs, eaves, and patio extensions (but not in full shade).
Take an Accurate Temperature
Different parts of the desert may experience lower temperatures, depending on the elevation and the amount of concrete in the area. If you live in a more rural area, use an outdoor thermometer and compare your actual temperature to the nearest city's. If you know your thermometer reads four degrees lower, you'll be prepared for frost, even if nearby forecasts call for a low of 35 degrees Fahrenheit.
Cover Your Plants
To protect your plants and trees from frost damage, they need to be covered. Use paper bags or boxes on sensitive ground covers or flowers. For trees and shrubs, the best covering materials include sheets, light blankets, or burlap. Hardware stores sell large sheets of light, porous cloth for this purpose. If you need to buy them, don't wait until the first frost, because they sell out quickly. You can also try buying sheets at thrift stores.
Avoid Covering With Plastic or Heavy Cloth
Plastic traps the moisture under the tarp and damages the plant. Heavy blankets are also ineffective—when they soak up moisture, they can become very heavy and break or even flatten branches.
Be Mindful When Covering
Make sure your cover touches the ground as this helps to retain all the warmth under the cloth. When possible, try to avoid touching the leaves with the material and aim to drape on the branches.
Protect Citrus Trees
Citrus trees that have not yet reached maturity, and especially lime and lemon trees, need frost protection. It can be challenging to cover large trees, but it's worth it to do the best you can. Unless it experiences a very severe frost, a mature citrus tree will most likely come back from frost exposure the following spring.
Keep Watering Your Plants
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 Rush to Uncover
Try to refrain from removing plant and tree frost covers if it's still dark, and preferably not until late in the morning the next day. Some of the coldest temperatures are just after sunrise.
Resist Pruning Until Spring
If frost gets to your plant, don't remove the damaged parts right away. They may look unhealthy for a couple of months, but those dead branches and leaves protect the part of the plant that's still alive. You can prune frost-damaged plants in the spring. Desert gardeners will also need to know when to prune and when to leave the plants alone.
When dealing with cold, freezing nights, it's better to do something for your plants than nothing. If you know the names of your plants, you can look them up at Desert-Tropicals.com for more specific care instructions.