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What to Cover in a Freeze: A Guide for Mild Winters

Frost and cold snaps can arrive unexpectedly, and knowing which vegetables, flowers, and landscape plants need protection during a freeze can make all the difference. This blog post provides a list of exactly which plants to cover—like tomatoes and peppers we try to overwinter—and which plants survive mild frosts without extra care.

What to Cover in a Freeze and Which Plants Survive Frost

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How cold does it need to be to freeze?

Freezing temperatures occur when the mercury dips to 32°F (0°C) or below. However, your garden’s microclimate might differ from the general forecast. That’s why paying close attention to the weather and regularly monitoring your yard is essential.

I use a weather station and a minimum/maximum thermometer to keep track of temperature variations. Sometimes, conditions in your garden can be colder than your phone’s weather app predicts. By staying alert to these differences, you’ll know precisely when to cover and protect your plants from unexpected frost.

  • Light freeze: 29°F to 32°F (-1.6°C to 0°C). Tender plants are often killed.
  • Moderate freeze: 25°F to 28°F (-3.88°C to -2.22°C). Causes damage to many plants.
  • Severe freeze: 24°F (-4.44°C) and colder. Causes heavy damage to many plants.
What to Cover in a Freeze and Which Plants Survive Frost

What to cover in a freeze and which plants survive frost

Cold weather often signals the end of the life cycle for many annual plants. Crops like melons, beans, squash, and cucumbers can’t tolerate cold conditions and will die when temperatures drop, so you’ll need to replant them in the spring.

However, some tender perennials—such as peppers, tomatoes, eggplants, and basil—can continue to produce and grow if protected from freezing temperatures. In warm-climate areas like the low desert of Arizona, shielding these plants from freezes can prolong their growing season. In this blog post, learn how to protect your plants from frost and freezing temperatures.


Frost Tender Vegetables: Killed or damaged by a light freeze

Harvest before cold temperatures:

Beans, Corn, Cucumber, Melons, Okra, Pumpkins (may continue to ripen after a frost, but storage life will be decreased), Roselle, Sesame, Squash, and Sweet Potatoes (harvest before soil temperature goes below 50°F [10°C]).

Cover during a freeze to protect and prolong the growing season:

Basil, EggplantGround CherryPeppersTomatillos, and Tomatoes (if prolonged freezing temperatures are expected, harvest tomatoes and allow them to ripen indoors). Learn more about how to turn green tomatoes red in this guide.


Frost Tolerant Vegetables

Frost Tolerant — withstands light and short term freeze (28°F to 32°F) (-2.22°C to 0°C)

Beets, Carrots, Cauliflower, Celery, Chard, Jeruselum Artichoke, Lettuce, Onion, Parsnip, Potatoes, Radish, Rutabaga, Strawberries (temperatures below 28°F (-2.22°C) will harm the blossoms), and Turnips.


Cold-Hardy Vegetables

Cold-Hardy — withstands moderate freezing temps (24°F to 28°F) (-4.4°C to -2.22°C) for short periods

Bok Choy, Broccoli, Brussels Sprouts, Cabbage, Chinese Cabbage, Kale, Kohlrabi, Leeks, Mustard Greens, Peas, and Spinach.


Which Landscape Plants to Cover During a Freeze

Many tender landscape plants will recover from light frosts but have unsightly damage if you don’t cover them. Covering tender landscape plants during a freeze may prevent damage. Remember, don’t prune frost-damaged plants until after the danger of frost has passed in the spring. Learn more about protecting citrus from freezing temperatures in this guide.

Frost-tender landscape plants:

Cover these plants during a freeze to prevent damage:

Frost-tender landscape plants include (but are not limited to) bougainvillea, some cacti, cape honeysuckle, coral vine, ficus, hibiscus, lantana, natal plum, myoporum, pygmy date palms, succulents, tropical plants (avocado, banana, guava, etc.), and yellow bells.


Which Flowers to Cover During a Freeze

Some flowers, including my favorite cool-season hardy annual flowers, aren’t bothered by mild frost events and don’t need to be covered. Others, however, should be covered if you want to overwinter them.

Frost-tender flowers:

Cover these plants during a freeze or remove plants before the weather cools.

Frost-tender flowers include (but are not limited to) ageratum, amaryllis, angelonia, begonia, calla lily, canna, celosia, coleus, cosmos, dahlia, four-o-clock, freesia, gazania, geranium, gomphrena, impatiens, lobelia, marigoldnasturtium, petunia, purslane, sunflower, tithonia, toothache plant, verbena, vinca, and zinnia.


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14 comments on "What to Cover in a Freeze: A Guide for Mild Winters"

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  1. Hi, Angela! How do we winterize or protect 9-month old Moringa trees in December? We live in Gold Canyon, AZ.
    We so appreciate your expert advice! Thank you!
    Merry Christmas to you & your family!

    Faith

    1. Hi Faith – Moringa branches, etc may die back but usually it rebounds in the spring. If you get freezing temperatures you can cover them at night to help protect a bit. Wait to prune off any damaged areas until after danger of frost has passed in the spring. Merry Christmas to you as well!

    1. Not sure. I did a quick google search and it looks like it will suffer damage if it freezes but may recover.

  2. What a great article! I found it on Pinterest. Is there a way to print it so I can refer to it often and write notes on it.
    Thanks, Chris

  3. Hi Angela! I follow you on Instagram and check for your incredibly helpful blog posts here. I wonder where I can find large metal hoops to support frost and shade cloth from my tall tomato plants. Thank you!

    1. Severe frost may damage individual stalks that are already growing, but new growth won’t be adversely affected.

  4. I was surprised to see fairy duster on the list of landscape plants that need covering. I have both the pink and red versions in my yard in Tucson and never cover them. Both have survived temps in the mid-20s unscathed. The red fairy duster blooms all year, even when we get the occasional snow!

  5. I have beautiful blooming Chysojaminum parkeri in a large barrel pot. Does it need to be covered if we are expecting 25 degree weather lasting 14 hours?

    1. It’s generally hardy to zone 6 so the roots would be fine. If you want to prevent any leaf damage you may want to cover it.

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