Jill is a former Master Gardener and Naturalist who enjoys cooking, abstract painting and stewardship.
How to Protect Plants From Frost
One day it's 65°F and sunny, and the next it's 32°F with snow on the ground. Yep, that's spring—a magical time of year filled with burgeoning life and fluctuating thermometers.
For many of us, spring presents one of the year's greatest gardening challenges: protecting tender new growth from damage due to cold. Frost damage, freezing death, root damage, and frost cracks on bark are four primary negative effects of severe drops in the temperature.
In early spring, when the threat of frost is especially great, closely monitoring weather conditions via weather radio, TV, and websites for reports of expected cold spells is imperative. That way, when frost is predicted, you can prepare for it. It's also a good idea to periodically check the temperature at ground level near your plants to see how cold it is for them and whether or not you need to do something about it.
This article will explain what frost is, how freezing temperatures affect plants, and what you can do about it. It will also provide easy and effective suggestions for protecting plants from frost, methods that can be applied to tender food crops like tomatoes and citrus trees, delicate potted plants like succulents and begonias, as well as other plants susceptible to extreme cold. Read on to find out how to protect your green friends from frost damage, freezing temperatures, and the cold hands of winter.
10 Easy Tips for Protecting Plants From Frost
Here are 10 easy, practical methods I've used to reduce frost's impact on my garden:
- Choose cold-hardy plants
- Place plants in frost-resistant spots
- Avoid frost pockets
- Harden off seedlings
- Cover plants before nightfall
- Protect plants with cloches
- Warm plants with water jugs
- Water before a frost
- Bring potted plants indoors
- Wrap fruit trees
Continue reading to find out more details about how to apply these methods in your own garden.
1. Choose Cold-Hardy Plants
Some vegetables and flowers are hardy souls that thrive in spite of (or sometimes because of) the cold. These kinds of plants are known as "hardy" because they can tolerate some amount of short-term freezing. By contrast, plants that are killed or severely injured by freezing temperatures are known as "tender."
Crocuses often push their way through snow to bloom, and a spring storm rarely gives narcissus, tulips, grape hyacinths, or pansies pause. There are also a wide range of tasty edibles that are resistant to frost, including:
- Calendula (pot marigold)
- Swiss chard
Experts at your local nursery are great sources of information about hardy plants appropriate to your zone. Native plants, particularly native perennials, will most likely be the best choices.
Which plants are sensitive to frost?
- Tender plants such as avocados, fuchsia, bougainvillea, begonias, impatiens, geraniums and succulents
- Edibles such as citrus trees, tropical plants, tomatoes, pumpkins, sweet potatoes, cucumber, okra, eggplant, corn, and peppers
- Spring-blooming shrubs and trees such as cherry, azalea, and rhododendron
- Tender perennials like canna, elephant ear, caladium, and dahlia. (Before a killing frost, consider digging these plants up and storing them in a dry, cool place.)
Read More From Dengarden
2. Place Plants in Frost-Resistant Spots
It's as true for plants as it is for real estate: location, location, location. Set out seedlings and store-bought spring plants in areas that are less likely to experience damaging cold.
As cold air moves to lower ground, it will pass by plants located on high ground or slopes. That's why it's best to place seedlings and other plants that are susceptible to frost in these elevated locations.
Placing plants by benches, fences, and walls—particularly if they are south- or west-facing—can provide additional protection, especially if the structures are dark in color. During the day, the structures absorb heat. Throughout the night, they radiate that heat, keeping plants warmer than they'd otherwise be. Nearby shrubbery also provides protection from light frosts.
What is frost?
Frost generally occurs on clear and calm nights, where there are few to no clouds to reflect warmth back to the ground and little to no wind to disperse warmer patches of air. The cold air then settles down to the lowest point, while the hot air rises up and away from the ground.
On these nights, frost can happen even if the temperature on your thermometer does not read below freezing. As long as the air temperatures at ground level dip below 32°F, ice crystals can still form on plants. This, in turn, disrupts the movement of fluids within the plant, depriving its tissues of water and drying it out. This is why leaves damaged by frost shrivel up and turn dark brown or black. If left in freezing temperatures for long durations of time without much protection, plants can easily die from desiccation.
Note: Frost can also occur when there is wind, but it is a chilling wind that then brings in even colder air, making matters worse.
3. Avoid Frost Pockets
Frost pockets are depressions in the ground. Cold air drains into these "pockets," and it can't get out. When this happens, plants located in the depressed areas can suffer frost damage. Avoid sowing seeds and bedding new plants in these low places.
4. Harden Off Seedlings
Before setting out seedlings, acclimate them to the outdoors by gradually exposing them to conditions outside. This process, called hardening off, will help you grow stronger plants that are more likely to withstand the vicissitudes of early spring.
Begin the hardening off process about 14 days before transplanting. When the weather's mild and above 45°F, place the seedlings outside during the day in a warm, shady spot that's protected from the wind. At night, bring them indoors.
After two weeks, the seedlings will be stronger, sturdier plants, ready for transplanting.
5. Cover Plants Before Nightfall
If you’re going to cover up your plants before a hard frost, do so before dusk. If you wait until darkness falls, most of the stored heat in your garden will have dissipated.
No matter what type of cover you use, make sure that it extends down to the soil on each side. Do not leave any openings for warmth to escape. If you can, it's also advisable to use stakes to keep material, especially plastic, from touching the foliage. Do not affix or gather your cover to the trunk, however, as this will prevent the heat radiating up out of the soil from reaching the plant. (See diagram below for proper covering.)
In the morning, after the frost has thawed, remove the covers. Failing to do so could cause the plant to break dormancy and start actively growing again, which would make it even more susceptible to frost damage in the future.
What can I cover my plants with to protect them from frost?
Here are just some of the items you can use to cover your tender plants:
- Bed sheets or blankets
- Drop cloths
- An inverted flower pot or bucket
- Milk jugs with the bottom cut out
- Frost cloths (These can protect some plants to temperatures as low as 20°F.)
- Garden blankets (These are good for garden rows or raised beds and will protect tender spring flowers and vegetables from cold en masse.)
It's also important to remember that covers don’t have to be elaborate or expensive in order to work. A row of sticks with newspaper, cardboard, or sheets and towels tented over them will do just fine. If you don’t have sticks, lay the covers directly over your plants. This, too, will prevent heat loss.
6. Protect Plants With Cloches
Strictly speaking, cloches are removable glass or plastic covers that protect plants from cold. Sometimes called bells or bell jars, most fit over individual plants, but some are large enough to cover a row. Like other covers, cloches should be placed over plants before the sun goes down and removed in the morning after the frost has thawed.
Glass cloches are highly ornamental. When you're not using them outside for frost protection, you can use them indoors over humidity-loving houseplants like violets.
You can also use plastic cloches, which are generally less expensive than glass ones. But because they are lightweight, they must be staked into the ground to prevent them from blowing away in high winds.
Note: Since cloches used for cold protection are temporary measures, you may opt to create your own makeshift versions. Flower pots, Mason jars, baskets, and milk jugs with the bottoms removed can all be placed over plants to shield them from freeze and frost.
7. Warm Plants With Water Jugs
Fill plastic milk jugs with water and place them in the sun, allowing them to soak up heat during the day. Before dusk, set the jugs around your plants and throw a cover over them. The water in the jugs will lose heat more slowly than the soil and the air, and the warmth it emits will help protect your plants from the cold.
8. Water Before a Frost
It may sound crazy, but watering around plants the night before a spring frost can actually protect them from freezing. During the night, the wet soil will release moisture into the air, raising the temperature and keeping plants warmer.
9. Bring Potted Plants Indoors
When frost is predicted, bring planters and hanging baskets inside. The roots of potted plants experience more severe temperature fluctuations than those planted in the ground. They'll reach lower temperatures, too. That's why potted plants are especially susceptible to root damage due to cold. It can cause their roots—particularly those near the edge of the pot—to turn spongy and black. Although root damage may not kill the plant, it will stunt its growth.
Just make sure when you bring potted plants inside that they don't have any insects or pests on them and aren't currently suffering from any diseases. This will not only potentially exacerbate the problem, but it could also infect your other plants.
If you opt to cover a hanging basket rather than bring it inside, place it on the ground first, and then place the cover over the basket to take advantage of the ground's relative warmth.
10. Wrap Fruit Trees
If you grow fruit trees, be sure to wrap the trunks in the fall with burlap strips or tree wrap. Most fruit trees have thin barks that are susceptible to splitting when temperatures fluctuate dramatically. Tree wrap will prevent this splitting, which is known as frost crack.
It's often a good idea to use multiple layers of cloth or weatherproof paper while still keeping the wrapping a bit loose. This provides more effective insulation. You should also extend the wrapping all the way to the ground and at least as high up as the lower limbs or branches. (See diagram below for proper technique.)
If necessary, this wrapping can be left on for the majority of the winter season.
Frequently Asked Questions
Here is some additional information regarding questions frequently asked about how to protect your plants from frost:
What factors affect the chances that a plant will die from frost?
- Cloud coverage: If there are more clouds in the sky to absorb and reflect heat back down to the earth, then your plants will stand a better chance of fending off frosts.
- Wind: Without enough wind to mix the rising warm air with the falling cold air, your plants will be more susceptible to the cold of the night.
- Humidity: Higher humidity raises the dew point and helps slow the rate of temperature change, decreasing the likelihood that frost will form on your plants. (This explains why dry deserts can shift from high heat to freezing cold so quickly.)
- Soil properties: The sun warms the soil during the day, and this heat then radiates out into the cooler atmosphere of the night. If your soil is deep, loose, heavy, and fertile, then it will release more moisture into the air. By contrast, thin, sandy, or nutrient-poor soil will not release as much moisture. Additionally, heavily mulched soil will prevent more moisture from releasing into the atmosphere, thus providing less protection on colder nights.
- Proximity of structures and other plants: Without other nearby plants and structures to provide shelter from cold winds and radiate back heat to your plants, they will be more vulnerable to frost.
- Age of the plant: Younger plants that are still actively growing or flowering will be more vulnerable to colder temperatures.
What are the different kinds of frost, and what do they mean?
The following table breaks down the different kinds of freezes and frosts, as well as the potential effects for plants exposed to even a few hours of freezing temperatures:
Types of Frosts and Freezes and Their Effects
|Temperature||Type or Name||Effects on Plants|
Light Freeze/Light Frost
Ice forms on the outside. Will likely only significantly harm or kill tender plants.
Moderate Freeze/Kiling Frost
Ice forms on the inside of the plant, which causes plant cells to burst. Will cause significant destruction to most foliage and vegetation. Fruit blossoms and semi-hardy plants will suffer extensive damage and potentially death. Even root-hardy perennials will be hurt.
Will cause severe damage to most all plants, leading to desiccation and death.
What are the first and last frost dates for my area?
The last frost date in the spring and the first frost date in the fall indicate how long your growing season will be. You need to know these dates so that you can determine when to start seeds indoors and when to purchase and plant nursery plants.
For freeze and frost dates in the U.S., you can visit the Farmer's Almanac or the National Oceanic and Atmospheric Administration (NOAA). Freeze-date tables, as well as other frost/freeze information, are also available through your local state cooperative extension office.
What do I do if I see frost damage?
Just because you see frost damage does not necessarily mean you need to take any drastic action. Many plants can be surprisingly resilient and might very well bounce back come springtime.
Your best bet is to wait until the weather begins to get warmer again (usually around March) and see if any new leaves sprout.
Should I prune frost-damaged growth?
It is definitely not advisable to begin pruning frost-damaged growth until the spring for a variety of reasons:
- Those damaged limbs and leaves will continue to trap heat within the canopy and help the plant make it through the winter.
- Damage is often not as bad as it may seem at first glance, and new growth may yet still emerge out of an area you might have thought was already dead.
- Pruning damaged limbs might stimulate new growth from your plant, and that new growth will be especially susceptible to frost (as well as your entire plant).
Only once new growth has sprouted from your plant in the following spring should you begin to prune dead or damaged limbs.
What doesn't help protect plants from frost?
Though you might have heard that these methods are effective, the following are almost certain to make matters worse:
- Large fires: This creates an updraft of hot air above the plants, which they cannot access. It also sucks in cold air from surrounding areas that could make the ground temperature even colder for your plants.
- Mulching: Though this can be of temporary help for situations such as trying to keep your deciduous fruit tree from prematurely breaking dormancy, it not only prevents the soil from capturing heat from the sun but also blocks much of that heat from rising up from that soil to help warm your plant. (If you do decide to use mulch for a short cold period, be sure to remove it once the danger of frost is over.)
- Bradley, Lucy (1998, April). Frost Protection. University of Arizona Extension. Retrieved on 19 October 2018.
- Mason, Sandra. Anticipating Frost - What to Do with Frost Sensitive Plants. University of Illinois Extension. Retrieved on 19 October 2018.
- Brown, Faith. How to Protect Plants from Frost. University of California, Division of Agriculture and Natural Resources. Retrieved on 19 October 2018.
- Day, Julie. How to Protect Your Garden from Frost and Freeze. Today's Homeowner. Retrieved on 19 October 2018.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
Questions & Answers
Question: It is supposed to rain and then frost. Can I still cover flowers with a towel even though it will get wet first then frost?
Answer: Yes, but you will need to use stakes or something to prop up the towels so that their weight when wet will not break down your plants. Also, try to get the covering all the way to the ground.
Question: Can I use garbage bags to cover plants to protect from frost?
Answer: No, don’t use plastic. It conducts cold and will cause damage to your plants.
Question: Are crabapple trees susceptible to frost at 29 degrees?
Answer: Although crabapple trees vary in cold hardiness by variety, they are susceptible to spring frost and can incur damage if the frost hits them as they're budding out of winter dormancy.
Question: Can I put rocks from a fire in the ground near my plant and cover it with a sheet as well?
Answer: I know hot rocks work for heating greenhouses and keeping campers warm at night, so I image they would work to protect plants in a make-shift tent. I would just be careful about how close to the plant I put the hot rocks. Good luck and be careful! If it works, please share your experience with us.
Question: Do pansies need to be protected from frost?
Answer: Pansies planted in the fall will last all winter into spring in Zones 6 and above. I believe some varieties do well in the colder zones as well. The leaves of ours sometimes darken due to hard frost, but no, your pansies should do fine without protection. I believe there's a picture of one of ours in the article above in bloom through spring snow.
Question: Can I use the chard in my garden after a deep frost?
Answer: Swiss chard is a frost-hardy plant, and cold weather will actually improve its flavor. Temperatures under 15 degrees, however, will kill it. If you're expecting temps that low, you should cover it with something like Reemay.
Question: I have a patio shade that goes all the way down to the floor. Can it help protect my plants from frost?
Answer: It sounds like it. Would your plants be covered on all sides? If not, you might want to give them a good watering and cover them lightly with newspaper, a sheet, or Reemay if you have it.
Question: Do you recommend watering a cold sensitive palm tree with hot water on a cold night?
Answer: I don't see much benefit in it. From what I've read, hot water stimulates growth but doesn't increase ground temperature. It's the evaporation that reduces frost.
Question: Can I use glass mason jars to cover new vegetable plants from frost or snow?
Answer: Sure! Use the jar just like a cloche.