How to Protect Your Garden from Frost

A landscape glistening under the light dusting of frost can seem like a fairytale image—in the depths of winter. 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. Knowing when to expect frosts in your area and keeping an eye on weather can help you prepare before a frost. Once you know it's coming, you can protect your plants from a frost by covering them or moving them inside.

What is "frost temperature" for plants?

Frost happens on clear, damp nights when the air temperature rapidly drops below 32 °F. In the morning, you'll see a layer of white or gray sparkles clinging to your windows, lawn, trees, shrubs or garden plants. Water vapor freezes and forms these shimmering ice crystals, but it also causes the water inside plant cells to form ice crystals, too. 

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 can even seem to taste sweeter if they've endured a light fall frost. Other, more sensitive plants—flowers and warm-season vegetables like tomatoes, melons and peppers—can die even in a light frost.

When the air temperature drops below 25 °F for at least 4 hours, it's called a hard frost or a killing frost because it can kill plants, including most annual flowers and vegetables. Your hardy and woody plants should be just fine, though they may have a little damage to new growth.

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. Many warm-weather plants are susceptible to damage from even a light frost, so it's good to be prepared.

Can I prevent frost damage?

Regular garden care throughout the year is the first step to protecting your plants from frost. Strong plants are better prepared to fight harsh weather, so keep yours well-nourished and watered. 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. Stop feeding plants in late summer or early fall (depending on conditions in your area) so that your plants aren't creating new growth that will be susceptible to frost damage. 

Keeping close tabs on the weather is also key to getting ahead of frost. You'll want to know when the average first and last frost dates in your area are, and start watching local weather forecasts well in advance. 

Set aside a pile of sheets or blankets before frost comes so you're ready to go. Covering your plants with a large sheet, blanket or towel can help increase the temperature around them by as much as 8 °F, which can be the deciding factor when it comes to whether or not your plants will freeze. If you're low on extra sheets, you can purchase fabric plant covers at your local hardware or home improvement store. Avoid plastic, as it is a poor insulator and won't do a good job protecting your plants. 

Building structures around your plants is another option to protect from frosts, as well as other stressors during the rest of the year like intense rain or scorching sun. "Houses" for your plants can also help extend the growing season, which is great if you garden in a cooler climate. Try a simple hoop house, cold frame or portable greenhouse. You can purchase these structures to assemble in your yard or garden, or build one of your own! 

How can I protect my plants from 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 to protect your plants:

• Water your plants just before midday. Moist soil can soak up max sunlight and hold the sun's heat before nightfall frost sets in. Be careful not to overwater—you want to moisten the soil, but not soak it.
• Spread some mulch. Mulch doesn't just make 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. Some crops do well in a light frost and a few might even survive a hard freeze, but mature veggies should be harvested before the cold comes. Otherwise, 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. 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, air-tight 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 plants at dusk. You'll want to cover flowers, vegetables, tropicals, citrus trees and any young, unestablished plants. Most established hardy plants will be fine, so don't worry about covering them. 
• Use large sheets, towels or blankets to create an impromptu tent for in-ground or raised beds. 
• "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. Add stakes underneath to prop up the cover and avoid crushing taller plants. 
• 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 cover individual rows or sections instead of the whole bed. 
• 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: leaves, stems, flowers and fruits, and even roots. Your plants will look soggy, limp or shriveled, and their green color may change to brown, black or even purple. Some leaves may look transparent or drained of color, sometimes referred to as "water soaked." 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 move containers back outdoors so your plants 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 revived. 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, but 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.

With a keen eye on your local weather report and some old sheets at the ready, you can relax 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!