This page includes information on:
- What causes frost damage?
- When is the frost period in Arizona?
- If your plants are damaged, when should you trim them?
- What can I do to protect my plants and cactus?
WHAT CAUSES FROST DAMAGE?
Despite Arizona's beautiful weather conditions during the winter we still can reach freezing temperatures.
While many frost-sensitive plants can tolerate freezing temperatures for brief periods, nights that dip into the low 30’s or below for several hours can be deadly for even the hardiest of plants.
This causes much damage to plants and creates waves of phone calls asking, "Are my plants DEAD?" Most likely the answer is no.
Frost damage in plants results from the liquid inside individual cells freezing and forming ice crystals. The crystals then rupture the tough cell walls. When the cell walls open the fluid inside will not be contained so when the ice melts the fluids simply drain out causing limp, dry, brown and black leaves.
Frost damage is progressive within plants. The softest tissues like leaves and tender new shoots are hurt first. With this in mind, the wise gardener waits until new growth starts in the spring to begin pruning off the damaged sections of the plant.
Typically our last frost date occurs in late February, although there have been rare occasions where frosts have been recorded in March. Waiting until then will actually make it easier to tell where tissue damaged by the freezes ends and live tissue begins. As new leaf buds emerge the green color will indicate where it is safe to prune away the dead foliage or stems.
This hibiscus has been badly effected this frost season. But it is NOT DEAD. The important thing to remember is that you must refrain from trimming your plants until spring when new growth is evident. You don't want to remove parts of the plant that are still alive!
The photo below shows a lantana that was badly frost bitten but is showing signs of regrowth.
If this lantana had been trimmed before spring, parts of the plant that were not dead would have been removed and it would take even longer for this plant to return to its full potential.
For more information on avoiding frost damage and the best times to prune, more information is available at from the University of Arizona at:
Protecting Your Plants
Protecting plants from freezing can be tricky. The plants most vulnerable to frost are soft woods, actively growing bloomers, and potted plants. Here's a few plants that are especially susceptible to frost damage:
- Natal Plum
- Red/Yellow Yucca
- Orange/Yellow Bells
- Cape Honeysuckle
- Red Bird of Paradise
- Citrus Trees
The greatest threat of frost usually occurs overnight when the temperature drops enough to freeze the moisture on plant leaves and buds. The signs of frost damage are usually visible within two to three days and are included blackened leaves or mushy leaves and buds. To protect plants from frost, you will need to cover them to keep the moisture from freezing.
Use sheets, light blankets or burlap to protect your plants and trees from frost damage. Hardware stores actually sell large sheets of light, porous cloth for this purpose. Don't have extra sheets and new ones are too expensive? Try buying sheets at a thrift store. 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.
Do not use plastic to cover your plants. This will trap the moisture under the tarp and damage the plant. Don't use heavy cloth or blankets either because they soak up the moisture they can become very heavy and damage the plant.
Make sure that your cover touches the ground all the way around. 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.
If frost gets to your plant, don't begin pruning until Spring! 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.
Use styrofoam cups to cover the growing tips on your cactus. This will protect them from frost. It will not harm them. Most cacti are dormant and not growing at this time. The growth put on this past summer is tender and needs to be protected.
When there is a threat of frost, cover your plants before sunset.
If your efforts to protect plants from frost fail or you simply forget, you will have to allow nature to take its course.
FebCo Backflow Preventer
During freezing temperatures the internal mechanism of your backflow preventer is prone to freezing and cracking. When this happens the backflow preventer will begin to leak.
The backflow preventer is located next to your outdoor hose spigot.
To prevent damage to this device be sure to insulate it well to avoid freezing. Below is a photograph of a commercially made cover for this specific need:
We do recommend adding a lock to these covers as they have been stolen from homes in the past. If you're interested in purchasing one of these covers from us, please email us at firstname.lastname@example.org.
Also, if you do notice any leaking coming from your FebCo unit please contact us immediately and we can repair this for you.