With more extreme weather events and fluctuations in temperature from season to season, knowing how to cover plants for frost has become increasingly important. What’s more, if you don’t know exactly when and how to cover plants for frost you can end up losing favorite specimens or missing out on that extra harvest. In this article, I’ll run down which plants need covering, and I’ll discuss some of the materials and methods best-suited for the task, including fabric, plastic, and mulches. That way, the next time you hear light frost or hard freezes are on the way, you and your plants will be ready.

Which plants need to be covered when frost is in the forecast

In addition to how to cover plants for frost, you’ll need to consider which plants need the protection most. Obviously, vegetables that typically thrive in warm weather—think peppers, tomatoes, eggplant, melons, squash, beans, and cucumber plants—will need extra protection. Depending on how late it is in the growing season, you may want to go ahead and harvest what you can from these tender plants before the forecasted frost hits. However, if you suspect there could be a few more weeks of warm, sunny days to come, you can simply protect them from this quick dip in temps and then uncover them again as soon as it’s safe to do so.

As for cool-weather crops like beets, lettuce, Swiss chard, carrots, parsnip, and cauliflower plants, these can withstand some light frost, but they may need protection if temperatures are expected to dip below, say, 28 degrees F (-2 degrees C). You needn’t worry nearly quite as much about cole crops such as broccoli, cabbage, Brussels sprouts, turnips, kale, and collards. These are all quite tough in the face of brief periods of cold weather. The same goes for spinach, peas, radish, and onion plants.

If you’re dealing with an unexpectedly late spring or early fall frost and you have flowering fruit trees or fruit trees in containers with blooms on them, you’ll want to protect these, too. I have a friend who uses this frost protector to protect her dwarf peach and apricot trees from frosts when they’re flowering.

Finally, frost-sensitive annual flowering plants, like petunias, impatiens, zinnias, marigolds, and nasturtiums, or tender tropical plants (think elephant ears, caladiums, begonias, and the like) will definitely need to be protected from frosts because they are extremely sensitive to cold. Covering these plants can protect them from a few nights of a light frost, but they will succumb if temperatures dip too low or stay low for more than a few hours, even if they are covered.

How low is too low when it comes to temperatures?

Although it’s easy to find conflicting advice on how to cover plants for frost, everyone agrees that most annuals, tropicals, warm-season veggies, and tender perennials simply can’t stand up to temperatures below 32 degrees F (0 degrees C.) If temperatures are expected to drop to the mid 30s (2 degrees C) or below, any frost-susceptible individual plants that you’re growing in pots need to be moved to a greenhouse, garage, or enclosed porch area for safekeeping.

When do you need to cover plants from frost

Check the latest USDA Plant Hardiness Zone map to get a sense for the average first and last frost dates for your area and regularly check the local weather forecast. If evening temperatures are expected to drop to the mid 30s (2 degrees C) or below, plan to cover plants that are susceptible to frost damage.

How to cover plants for frost using fabric

If the weather forecast catches you off-guard, deciding how to cover plants for frost and what you’ll use to do it may depend on the materials you already have on hand. Fortunately, light bed sheets and blankets can work in a pinch. Specially designed floating row cover rated for use in cold weather may work better still. I also like the Maxi Garden Quilt from Gardener’s Supply Company for larger plants.

Whatever fabric covering you choose, you should fashion some type of frame to drape it over. This could be a series of garden stakes, some low fencing, or a commercially available tunnel. (The point of this configuration is to trap in the soil’s heat while simultaneously keeping frost from settling on plant leaves.)

How to cover plants for frost using plastic

Here are some quick tips for how to cover plants for frost using plastic:

• Cut the bottoms off of large plastic bottles or milk jugs to create cloches for covering individual plants. (You can also purchase larger plastic cloches like these.)
• Have a raised bed? Use scrap lumber to create a slightly elevated lip and then top with a durable, flat panel of polycarbonate (greenhouse) plastic.
• You can also purchase pre-made garden bed covers made from plastic to protect plants from light frosts.
• Plastic sheeting caveat: some plastic tarps or plastic drop cloths are not ideal for frost protection, because they restrict air flow to your plants and they may be too thin to truly guard against the cold.

It’s best to not let plastic coverings come in direct contact with foliage; prop plastic sheeting up off of plants using metal or PVC hoops.

Other materials for protecting plants from frost

Once you understand how to cover plants for frost using fabric and some types of plastic, you’ll likely begin to see the frost protection potential in many other items and materials. For instance, you can make simple cold frames by arranging straw bales into rectangle shapes and then topping with old windows. Akin to mini greenhouses, these can be used to harden off spring seedlings or prolong your fall harvest.

Even a heavy layer of mulch made from chopped, dried leaves or pine straw can be enough to protect low-growing plants from light frost. (Just be sure to expose the plants again once the coast is clear!) Upside down plastic nursery pots can be used to cover plants at night, as long as they are removed mid-morning. Inverted cardboard boxes or small waste paper baskets also work to protect plants from light frosts.

Also worth noting, moist soil holds heat better than dry soil does, so, make sure to water before a frost event.

When to remove frost covers

Temporary frost covers meant to protect plants from light night-time frosts can be removed when the sun comes up and the frost melts from the lawn. Just be sure to put them back over the plants if another frost is forecasted.

For longer-term frost covers, such as cold frames and mini hoop tunnels, know that they may raise the soil temperature by as much as 10 degrees, so, if the weather warms up again, you should at least partially remove the plant covering so that your plants don’t smother or burn. In spring, you can remove the cover completely after the last average frost date has passed.

What happens if it didn’t work

If your frost protection has failed, you could see small amounts of damage to plant buds or leaves which can easily be pruned off. A cold snap that is very severe or prolonged, on the other hand, can destroy the plant’s cell walls, resulting in a badly wilted or completely blackened—and dead or dying—plant, especially if it is a frost-sensitive species. In this case, it’s best to remove the plant entirely and toss it on the compost pile.

If a hardy perennial plant faces frost damage, simply leave the plant alone. It will most likely regrow new foliage once the cold temperatures have passed.

The cold facts

Now that you’ve learned just how to cover plants for frost, your garden will be less vulnerable to those inevitable cold spells that pop up in late spring and early fall. Although you need not worry about your hardy perennials, plenty of other plants require TLC if you want to coax a little extra life out of them despite cold weather. Are evening temperatures expected to drop to 35 or 36 degrees F (1.6 to 2.2 degrees C) or below? You can protect against freeze damage—and prolong your harvest in the process—by using floating row cover fabric, covered tunnels, plastic cloches, and more.

For more on protecting plants from weather and pests, please visit the following articles:

• How to use frost cloth
• Plant covers for pests and weather
• Winter shrub covers
• Protecting hydrangea in winter
• Garden bed covers for the veggie garden