What to Cover in a Freeze: Frost Protection in the Garden

Living in a mild winter climate means that you may try to push the boundaries of what can be grown throughout winter. Frost and cold weather can come on quickly, and knowing what to cover in a freeze can mean the difference between life and death for some plants. Gather items like frost cloth and burlap before a freeze hits. 

This article shares tips for protecting your warm-climate garden from freezing temperatures, such as knowing the most common times for frost, utilizing effective plant placement in your garden, and knowing what to have on hand to protect plants. These tips will give your garden the best chance of surviving freezing temperatures.

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6 Tips for Protecting Your Warm-Climate Garden from Freezing Temperatures

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1. Learn when to expect freezing temperatures

An essential tool in knowing when freezing temperatures are most likely is knowing your first and last frost dates. You can look them up here using your zip code if you live in the United States.

Frost is most likely on clear, calm nights with few clouds and low humidity. Cold winds will also decrease the temperature.

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2. Choose the best location in your yard for frost-tender plants

Cold air moves downslope and settles in the lowest spots. The cold spots in your yard are good for planting fruit trees that need chill hours and other cold-loving plants.

Plant frost-tender trees and plants in the warmest areas of your yard. An area with a western or southern exposure with reflected heat from a block wall will be warmer than other areas in your landscape. The heat absorbed by a block wall throughout the day will radiate during the night.

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3. Understand what makes a plant have frost damage

Frost on a plant disrupts the movement of fluids within the plant and dries it out, leaving behind brown and crispy damage.

Some factors that make plants more or less susceptible to damage from freezing temperatures include:

• Dormancy — A plant that is dormant will have less damage than a tree or plant that is actively growing. This is why a sudden frost early in the season will often do more damage than a frost later in the season after plants have adjusted to colder temperatures.
• Watering — Well-watered plants withstand freezing temperatures better than dehydrated plants. The water in the soil also helps to insulate the soil.
• Pruning — Newly-pruned areas of the plant are more susceptible to frost damage.
• Newly planted — Less-established root systems of new plants are more likely to be damaged by frost.
• Plants in containers — Container-grown plants are subject to higher fluctuations in temperature than in-ground plants. They are more likely to suffer damage in a freeze.
• Lower temperatures, longer exposure to freezing temperatures, and rapid drops in temperature cause more damage.

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4. What to cover in a freeze and what not to cover during a freeze

Cold weather signals the end of the life cycle for many annual plants. In warm-climate areas like the low desert of Arizona, protecting from freezing temperatures may prolong the growing season.

Peppers, tomatoes, eggplants, and basil are a few plants that, if protected from a freeze, may continue to produce and grow. Other tender plants will need to be replanted in the spring.

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What to cover in a freeze: Tender — injured by a light frost (cover during a freeze or harvest before cold temperatures).

Basil, Beans, Corn, Cucumber, Eggplant, Ground Cherry, Melons, Nasturtium, Okra, Peppers, Pumpkins (may continue to ripen after a frost, but storage life will be decreased), Roselle, Squash, Sweet Potatoes (harvest before soil temperature goes below 50°F(10°C), Tomatillos, Tomatoes (if prolonged freezing temperatures are expected, harvest tomatoes and allow them to ripen indoors)

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Frost Tolerant– withstand light and short term freeze (28°F – 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) Turnips

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Cold-Hardy — withstands moderate freezing temps (24°F – 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, Spinach

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What to cover in a freeze: Protecting citrus during a freeze

Freezing weather can cause severe damage to citrus trees. 

• Young trees are more susceptible to frost damage. Cover citrus during a freeze for 3-5 years after planting.
• Fruit damage may occur after several hours of temperatures below 27°F (-2.7°C). Frost-damaged fruit will have a dry interior.
• Wait until after the danger of frost has passed in the spring to prune frost-damaged limbs and branches. 

Some citrus trees are more cold-hardy than others. 

• Kumquat and mandarin trees are most cold-hardy (18°F – 20℉) or (-7.7°C to -6.6°C).
• Grapefruit and orange trees (tolerate to Mid 20’s℉ ) (-3.88°C)
• Lemon, and especially lime trees, are the most frost-sensitive, often suffering damage at 32℉ (0°C). They are highly frost-sensitive; choose the warmest areas of your yard for planting. Lemon and lime trees often do not go into dormancy, so frost affects them more than other citrus.

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What to cover in a freeze: Frost-tender landscape plants

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. Don’t prune frost-damaged plants until after the danger of frost has passed in the spring.

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, fairy dusters, ficus, hibiscus, lantana, natal plum, myoporum, pygmy date palms, succulents, tropical plants (avocado, banana, guava, etc.), yellow bells.

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Frost-tender annual flowers include (but are not limited to): aster, ageratum, gazania, geranium, lobelia, marigold, nasturtium, verbena, and zinnia.

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

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5. How to protect plants during a freeze

• Water plants well before a frost event. Moist soil may absorb more heat and radiate it throughout the night.
• Cover plants before sundown to trap the stored heat from during the day. If you wait to cover it until after nightfall, the heat may have dissipated.
• Use frost cloth, burlap, drop cloths, sheets, blankets, or even newspapers to cover plants. Do not use plastic.
• Cover the plant completely, allowing the cover to drape down to the soil all around the plant. This traps the warmth inside. Don’t gather the cover around the trunk; it won’t trap radiated heat from around the plant.

• Wrap trunks of frost-sensitive trees and young trees loosely with multiple layers of cloth. This can be left in place all winter.
• Use styrofoam cups to protect the growing tips of cactus.
• Add heat by wrapping heat-generating light bulbs (not LED) below the foliage of the covered plants. Take care not to have bulbs burn the bark or branches.
• Remove sheets or blankets in the morning after the frost thaws. Dormant plants can be brought out of dormancy by keeping the plant covers on and trapping the heat during the day. Actively-growing plants are more likely to suffer frost damage than dormant plants.
• Frost cloth can be left in place for several days without harming the plant.

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6. What to do after a frost

Did your perennial plants suffer frost damage? Don’t prune them right away. The damaged limbs and branches protect the plant from further frost damage.

Before pruning, wait until the danger of frost is past in the spring and you begin to see new growth. Prune back to just before where the new growth begins.

Severely damaged tomatoes, peppers, and other annual plants may need removal.

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