How to Protect Your Garden from Frost

Photo credit: Shutterstock/Amanda J Jackson

A landscape glistening under the light dusting of frost can seem like a fairytale image—in the depths of winter, that is. When you're not prepared for it, the sight of these frozen crystals can send shivers down any gardener's spine. Frost is spring's favorite late-season trick and winter's early hello, creeping in to chill your plants down to their botanical bones.

Fortunately, a late or early frost doesn't have to spell doom for your garden. If you know your first and last frost dates, how to bundle up your plants, and keep an eye on the weather, you can help shield them from the chilliest of nights.

What exactly is frost?

Frost is the layer of white or gray sparkles you see clinging to your windows, lawn, trees, shrubs, or (gasp!) garden plants. It happens on clear, damp nights, when the air temperature rapidly drops below 32ºF. Water vapor freezes and forms the ice crystals you see on surfaces—but it also causes the water inside plant cells to form ice crystals, too. Yikes, right?

Some established plants can survive a light frost; that's when the temperature hovers between 28°F and 32°F for a few hours. Crops like spinach and kale actually prefer this cool weather (and seem to taste better if they've endured a light fall frost.) When the air temperature drops below 25°F for at least 4 hours, though, it's called a hard frost or a killing frost, because, well, it kills most plants.

Even if you're lucky enough to live in a zone where you can garden year-round, temperature dips and light snowfall aren't out of the question, so it's good to be prepared.

Can I prevent frost damage?

Keeping close tabs on the weather is key to getting ahead of frost. However, regular garden care can also help with drastic dips in temps. Strong plants are better prepared to fight harsh weather, so keep yours well-nourished and watered from the very start of the growing season. Every 3 months, feed your plants Miracle-Gro® Shake-'n-Feed® All-Purpose Plant Food. It'll help them grow robust roots and improve their response to less-than-ideal conditions.

Covering your plants can help increase the temperature around them by as much as 8ºF, which can be the deciding factor when it comes to whether or not your plants will freeze. One simple solution is to build a simple hoop house to cover them. It can not only help keep your plants warmer in frosty conditions, but also dry when it's wet and shaded in the scorching sun. Another option is a cold frame or portable greenhouse. Both can help extend the growing season, too, which is great if you garden in a cooler climate.

How can I prep for frost?

Meteorologists typically issue frost warnings the day before things are going to take a turn, giving you a window of time to prepare. If frost is coming your way, take these steps.

• Water your plants at midday. Moist soil can soak up max sunlight and hold the sun's heat before nightfall and good ol' frost sets in. Be careful not to overwater—you want to moisten the soil, but not soak it.

• Spread some mulch. You know that stuff that makes your garden look nice? It also helps your soil retain heat. Spread a 3- to 6-inch layer of mulch over any exposed soil. Avoid your plants' stems, though—you want to keep the mulch at least 3 inches away.

• Harvest mature vegetables. You will not recreate the freezer section at your local grocery store by leaving mature veggies on the plant. You'll likely end up with just more for the compost pile once the weather is better.

• Move container plants indoors. Relocate what you can to a garage, shed, or basement—any place that shelters your plants from freezing air but isn't so warm that it'll shock them. (Pro tip: Check your plants for insects or disease before moving them inside, so you don't introduce any problems to your houseplants.) If you can't bring containers indoors, snuggle them close together to trap heat and cover them with a sheet or other lightweight material.

• Protect individual plants. Turn bowls, buckets, (non-wicker) baskets, and other items upside-down to cover your plants, taking care not to crush foliage or break stems in the process. This works particularly well for any flowers that are dotting your landscape. Make sure your covers reach all the way to the soil while accommodating each plant's height. Weigh them down with a stone or brick.

• Cover your beds at dusk. Use large sheets, towels, or blankets to create an impromptu tent for in-ground or raised beds. (Avoid plastic, as it is a poor insulator and won't do a good job protecting your plants.) "Tuck" plants in by bringing covers all the way down to the soil line. Keep covers high enough to allow air to circulate between your plants, and if there's a danger of wind, anchor the corners and sides firmly with stakes, pins, or heavy objects. (For in-ground beds, you can anchor rows or sections instead of the whole bed.) Add stakes underneath to prop up the cover and avoid crushing taller plants. Use newspaper over new seedlings and tender plants, laying it down gently and securing the corners.

What does frost damage look like?

Frost damage can happen anywhere on a plant: foliage, stems, flowers, and fruits, and even roots. Your plants will look soggy, limp, or shriveled, and their green color may change to brown or black. Some leaves may look transparent or drained of color. When warm weather returns, leaves may crisp and curl.

Vegetables that have been injured by frost can look spotted, brown, blistered, cracked, or mushy, or appear to have been soaked in water. Some, like broccoli and turnips, may give off a bad odor after they thaw.

How can I save frost-damaged plants?

Many plants can survive frost, while sadly, some cannot (tender plants with new growth are most likely to suffer). When the sun comes up, take the covers off your plants and containers back outdoors so your leafy friends can bask in sunlight and fresh air. Then, follow these tips.

• Don't prune plants with frost damage right away. Dead branches and leaves can actually provide protection while a plant heals, and some plants will outgrow damaged leaves. If parts of your plant appear alive, give them a chance to bounce back before pruning. You can prune once you see new growth.

• Don't fertilize frost-stressed plants. Though your garden may look dismal, resist the urge to give your plants a boost of nutrition until they're looking revitalized. They need to put their energy into healing, not creating new growth. A good rule of thumb is to wait 2 weeks after the frost to begin feeding again.

• Do keep watering your garden. Watering after a frost can actually help thaw frozen soil and aid plants' recovery. Frost-damaged perennials may seem dead, but their roots could be healthy. Maintaining moist soil will help insulate their roots and keep them alive.

• Do keep the faith! Give annuals a few days before making a decision on whether they'll stay or go, and leave any perennials in the ground. Toss plants that won't recover, as well as any inedible vegetables, onto your compost pile so they don't invite pests or disease. Then, if it's still early enough in the season, go ahead and replant!

If, despite your best efforts, you're frustrated by repeated frost damage, have a look at our zone-planting guide to make sure you're not starting too early. You should also check your plant choices to ensure they're a good match for your hardiness zone. Hardy annuals and perennials can grow well in areas prone to frost and temperature swings, while tender plants prefer warmer, more consistent growing conditions. Native plants are ideal, since they're already accustomed to growing in your region. Try growing some different plants next season, and you may discover some new favorites. (Consider it the silver lining to this frost-filled cloud!)

With a keen eye on your local weather report and some old sheets at the ready (and a few other tools), you can feel chill about a night of frost while keeping your plants nice and warm. When you're prepared, those frozen crystals don't stand a chance against your garden!