Frost Protection for Phoenix Yards
Frost in the Valley usually shows up between late November and mid February, and it comes on calm, clear nights. Tropical plants like bougainvillea, hibiscus, lantana, ficus and young citrus are the ones to cover. Use frost cloth or an old sheet, never plastic, and leave the damage alone until spring.
When frost happens and which nights to watch
- Most years the frost window runs from around Thanksgiving to around Valentine's Day. Hard freezes most often land in late December or early January.
- Central Phoenix gets fewer frost nights than outlying areas. Mesa, Buckeye and low spots can see frost weeks earlier and later.
- Calm, clear nights are the ones to watch.
- The coldest point comes right around sunrise, not at midnight.
- Cold air settles to the lowest spot, so the bottom of a slope runs colder than the rest of the yard.
- Cover tender plants before sundown on nights the forecast low is near freezing.
How to cover and protect
- Use frost cloth or sheets, never plastic. Frost cloth works best. Cotton sheets, burlap and old blankets also work.
- Go all the way to the ground. The warmth comes up from the soil, so drape the cover to the ground and weigh the edges with rocks. Don't bunch it around the trunk.
- Keep it off the leaves. Prop the cover on stakes or a frame so it makes a tent instead of pressing on the branches.
- Uncover in the morning. Take sheets off once the sun is up and it has warmed up, never while it's still dark. Frost cloth can stay on a few days in a row, but not all winter.
- Water a day or two ahead. Moist soil holds more heat than dry soil. Water tropical plants and trees at the base, then turn off sprinklers so leaves are dry by night.
- Keep cactus and succulents dry. They handle cold better when the soil is dry, so skip watering them before a freeze.
- Add a little heat. Old-style Christmas lights or an incandescent bulb under the cover add warmth. Keep bulbs off the cover and away from water.
- Move pots. Potted plants get colder than plants in the ground. Move them under a patio, against the house or into the garage for the night.
- Cap cactus tips. Put foam cups over the tips of columnar cactus. The growing tip is the part that gets hurt.
- Wrap young citrus trunks. Loose cloth or paper around the trunk of a young tree protects it and can stay on all winter.
Which plants need it and which don't
| Plant | Frost note |
|---|---|
| Bougainvillea | One of the first plants to burn in a frost. |
| Hibiscus | One of the hardest hit in a frost, along with bougainvillea. |
| Lantana | Often freezes back but regrows fast in spring. |
| Yellow Bells and Orange Jubilee | Tips and leaves burn in a hard frost. |
| Natal plum | Young plants and new growth are the most at risk. |
| Indian Laurel Ficus | Especially cold sensitive. Young trees need covers. |
| Lemons and limes | The least cold hardy citrus. They can take damage in the mid to upper 20s. Young trees need covers most. |
| Mexican Fencepost and Organ Pipe | Tips can burn in the mid 20s. Cap the tips with cups. |
| Elephant's Food and aloes | Many succulents need covers or a spot under the patio. |
Desert trees and cactus handle a normal Valley frost without covers. Palo verde, mesquite and prickly pear take much more cold than the plants above.
After frost damage
- Leave the brown leaves and stems on. They shield the rest of the plant from the next cold night.
- Wait to prune until spring, once new growth starts, usually in March. Pruning early pushes out soft growth the next frost hits harder.
- Damage often looks worse than it is. Many plants that look dead leaf out again in spring.
Common questions
Can I cover my plants with plastic?
No. Plastic passes the cold through and burns leaves where it touches. Use frost cloth, cotton sheets, burlap or old blankets.
When should I take the frost cover off?
Take sheets off in the morning once the sun is up and it has warmed up. Frost cloth can stay on for a few days during a cold stretch, but take it off when the cold passes.
Should I water before a freeze?
Yes for tropical plants and trees, a day or two before. Skip cactus and succulents.
Do I need to cover my cactus?
Prickly pears handle Valley cold fine. Columnar cactus like Mexican fencepost and organ pipe benefit from foam cups on the tips.
When can I prune frost damaged plants?
Wait until spring, once nights stay warm and new growth shows, usually in March. Cutting early exposes the plant to the next frost.