How To: Protect Plants from Frost
Prepare for dipping temperatures now so your garden will come through the winter beautifully.
Unexpected early fall and late spring frosts—periods when outside temperatures go below freezing (32 degrees Fahrenheit)—often catch home gardeners off-guard, nipping tender fruit buds, cutting short vegetable harvests, and killing houseplants that were left outdoors. When a plant is damaged by frost, leaves appear wet and limp due to ice forming within the cells, which interrupts the natural flow of water throughout the plant. Tender annuals usually die from frost exposure, and while trees and shrubs will survive, they’ll lose any buds or mature fruit.
Local weather forecasts can tip you off to frosts, but you shouldn’t depend on them entirely. Pay attention to clues like the state of the sky, keeping in mind that temperatures are more likely to dip dangerously on clear nights that lack insulating cloud cover. But why wait till the last minute to swoop in and save your plants? The best way to prevent frost damage is to gather and implement strategies in advance of a cold front. Just follow this guide for how to protect plants from frost—you and your garden will be glad you did!
IT’S A WRAP
Wrapping the entire branch system of small trees or shrubs with horticultural frost cloth, burlap, plastic sheeting, or even old bedsheets will keep the temperature underneath a crucial few degrees warmer than outside. Use twine or clothespins to hold the material in place.
Two flat bedsheets sewn on three sides will provide a large covering for a small fruit or ornamental tree, such as a dwarf or semi-dwarf peach or cherry tree of approximately 12 to 15 feet. Place it lightly over the tree, covering the branches, and secure the excess around the trunk with twine. For smaller frost-susceptible species like tomato or pepper plants, set a stool or a patio chair over them drape it with a sheet.
When an extra cold night (below 30 degrees Fahrenheit) is predicted, tuck an outdoor light bulb in an approved outdoor fixture under a large wrap to produce additional heat. Position the bulb where it is sheltered from rain and cannot make contact with either the wrap or the branches to prevent the risk of fire. As a further safety measure, use an exterior extension cord with an inline ground fault circuit interrupter (GFCI). A 40-watt incandescent bulb will often generate sufficient heat under the wrap to protect a small tree, but skip the LEDs—they don’t produce heat.
Remove wraps the following morning as soon as temps rise above freezing, so plants can receive direct sunlight and air circulation. Keep the materials handy in case you need them again.
You can purchase glass or plastic domes, called “cloches,” to shelter vulnerable seedlings in early spring—or DIY them by cutting the tops off opaque plastic milk jugs. Other spur-of-the-moment cloches include inverted buckets and flowerpots. Simply place cloches over young vines and shrubs, such as tomatoes and peppers, to protect plants from frost.
If the temperatures are expected to hover around the freezing mark, cover long rows of seedlings lightly with loose straw or mulch to help the soil retain heat a bit longer. This will only work for light frosts, however. If temps fall below 32 degrees Fahrenheit for longer than a few of hours, place cloches over the rows.
Penny-pincher tip: If you’re planning on starting a large garden, save milk jugs throughout the winter to use as cloches in spring.
WATER FOR WARMTH
Well-watered plants are stronger and more likely to withstand exposure to a touch of light frost. Water retains heat and has an insulating effect on plant cells. A thirsty plant is more likely succumb to light frost because its cells are already stressed. So saturate vegetable and annual flower beds early in the day if frosty temps are in the forecast. That will give plants plenty of time to absorb the water before the temperatures drop.
For additional protection, fill plastic jugs with water and set them beside plants. At night, cover plants and jugs with fabric or sheeting. During the day, the water in the jugs will warm up. At night, they will radiate the retained heat to the air beneath the cover to keep plants warmer.
TAKE ‘EM INSIDE
In warm weather, keeping such popular tropical houseplants as jasmine, philodendron, and shefflera outdoors in protected areas like covered patios allows them to bask in light and air. Alas, just one premature frost can kill them, so don’t risk leaving them out too long! To prep plants for their winter indoors, water early in the day and mist foliage with water to remove any garden pests that have taken up residence. Then let plants dry until the evening before moving them inside.
BRING IN THE BULBS
Tender bulbs and tubers, such as calla lilies, elephant ears, and gladiolas, should be dug up before freezing temperatures arrive and stored in a cool, dry place (around 50 degrees Fahrenheit). A basement makes a good storage spot. Dig cautiously, taking care not to do damage with your shovel or trowel. Rinse bulbs and tubers with water to remove stuck-on soil, and then let them dry completely before layering them in a ventilated box filled with clean straw or peat moss.
TRY A SPECIAL SPRAY
Anti-transpirant foliage sprays, available from garden centers, help guard ornamental plants including rhododendrons, azaleas, and laurels from light frosts. These sprays impart a light coating of polymer film to the leaves, which is designed to protect plants’ leaves for up to a month by sealing in moisture. If the temps dip below 30 degrees Fahrenheit for more than a few hours, however, or if the leaves are not adequately covered by the spray, plants may still suffer frost damage.
Protecting plants is one of the most important garden tasks to do this fall. To learn about the other necessary duties, check out this video: