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When winter begins to lift and the tender shoots of perennials emerge, an overnight frost can quite literally nip new growth in the bud. Even in mild-winter regions, frost can have damaging effects on cold-sensitive garden favorites like citrus trees, bougainvilleas, fuchsias, salvias and succulents. Luckily, many plants can be saved from harm when the temperature dips below the freezing point (32 degrees Fahrenheit, or 0 degrees Celsius) with a few simple precautions.
Check the forecast. In early spring (or throughout winter in mild climates), pay attention to weather forecasts. For nights when a freeze is predicted, gather basic supplies, such as frost blankets (available at nurseries) and stakes, or invest in more expensive cold frames and cloches.
Cover plants before nightfall. If a frosty night is forecast, cover tender plants like angel’s trumpet (Brugmansia spp.), bougainvillea, citrus, fuchsia, penstemon, salvia, succulents and tree ferns. Young plants and those that have been recently planted can be more vulnerable to frost damage than well-established ones.
To cover plants, place stakes around small to medium-size plants and drape frost blankets over the stakes so that, ideally, the blanket covers but does not touch the plant. For larger plants like gardenia and tree ferns, drape coverings over the crown and wrap the trunk. Always remove the covering in the morning. Forgot to buy frost blankets? Old bed sheets or lightweight blankets can be used as well and are preferable to plastic tarps.
Use a cold frame. To extend your potential for growing cold-tender plants — such as potatoes, lettuce, spinach and other edible greens — and get a jump-start on starting spring seedlings, consider investing in cold frames. These glass-topped frames trap heat and moisture, creating a greenhouse environment for tender plants.
Protect sensitive plants with cloches. Named for the French word for “bell,” glass cloches work like cold frames on a smaller scale by creating warm, moist environments for tender plants and seedlings in the ground. Place cloches over small plants in the afternoon, and the trapped warmth will help the plants survive a frosty night. Cloches used to cover plants in full sun can get too toasty on a warm day, so either remove them or put a wedge of wood under one side to allow ventilation. Plastic gallon milk jugs can be cut and used as an inexpensive — if less charming — alternative to cover tender plants in beds.
Spread mulch. Help protect the shallow roots of tender shrubs and perennials from ground freezes by spreading a 3- to 4-inch layer of wood chip or straw mulch. Mulch can be purchased at nurseries and garden supply stores by the bag or in bulk.
Bring small potted plants indoors. The easiest way to protect succulents and tender herbs from an overnight freeze is to bring them inside. If you have a sunny spot for them, keep them indoors through the cold weather. Otherwise, bring them back outside during the day.
Move large potted plants under eaves. Cold wind can intensify the harmful effects of frost by removing moisture from foliage faster than the plant can take up water from the roots. To cut down on this damage, move larger potted plants to sheltered areas, such as under the eaves, beneath the canopy of large trees or into the garage for the night. Provide extra protection by wrapping the plants with frost blankets.
Water well. It may seem counterintuitive to water a garden before a freeze, but providing frost-tender plants with a good drink in the daytime makes plants better able to withstand colder night temperatures. Water early in the day so that the plants have time to absorb moisture before the temperature drops. Avoid spraying the foliage, which can freeze if not given time to dry off.
Wait to cut back frost-damaged plants. Although brown foliage and crispy stalks look unattractive, the damaged growth actually helps protect the lower parts of the plant from future freezes.
Hold off on pruning plants that have been damaged until all risk of nighttime freezes has passed. If you cut back the plant too early and have more nights with frosty temperatures, the shock of pruning and freezing can kill the plant.
- Cold Snap Care & the Benefits of Frost Covers for Plants
- How to protect blooming trees from hard-freeze
- How to Keep Plants from Freezing in Vegetable Gardens
- Dreaming of a beautiful, productive veggie garden?
- Protect Your Plants In A Freeze – How To Protect Plants From Freezing
- At What Temperature Do Plants Freeze?
- How to Protect Plants from Freezing
- Protect Your Plants from Frost Damage
- How to Save a Cold-Damaged Plant
Cold Snap Care & the Benefits of Frost Covers for Plants
Know The Limits
In order to understand what steps to take when freeze warnings threaten, you need to know the point at which treasured greenery fades to frost-burned brown. The general rule of thumb is that most plants freeze when temperatures remain at 28°F for five hours.
Of course, there are exceptions to this rule. Seedlings, with their tender new leaves, often give up the ghost when temperatures dip to 32-33°F. Tropical plants have differing low-temperature thresholds. Some keel over when temps fall to 40°F; others crumble at 35°F. Other plants are just hardy by nature and can withstand temperatures as low as 18-20°F. To find the threshold for your plants, search garden books and online resources.
Quick Fixes For Frost Warnings
Pick It Up – The easiest cold-protection scheme is to move plants out of harm’s way. This works with seedlings in flats and potted plants. Moving plants under a deck, into a garage or shed, or onto a porch with a roof often offers ample protection.
Count On Water – Water soil just before sundown to raise overnight air temperature around plants as the water evaporates. Fill gallon jugs or buckets with water and place them in the sun during the day. At night, move them near endangered plants. The water will moderate air temperatures; if it freezes, it will release heat. For greatest effect, paint a few water-holding containers black to maximize daytime heating.
Keep Air Moving – Cold, still air does the most damage to plants. Stir a breeze all night with an electric fan to keep frost from forming on plants. Remember to protect electrical connections from moisture.
Cover Plants – Protect plants from all but the hardest freeze (28°F for five hours) by covering them with sheets, towels, blankets, cardboard or a tarp. You can also invert baskets, coolers or any container with a solid bottom over plants. Cover plants before dark to trap warmer air. Ideally, coverings shouldn’t touch foliage. Anchor fabric coverings if windy conditions threaten.
In the morning, remove coverings when temperatures rise and frost dissipates. Heat from the sun can build beneath solid coverings, and plants can die from high temperatures.
Break Out Blankets – Keep gardening blankets, often called row covers, on hand. These covers are made from synthetic fibers or plastic in varying thicknesses. Lay row covers directly on plants, or create a tunnel by suspending them over a bed using stakes.
Turn On Lights – An incandescent light bulb generates sufficient heat to raise nearby air temperature enough to protect a plant from the deep freeze. Bulbs must be close to plants (within 2-3 feet) for this technique to work. (Fluorescent bulbs don’t generate enough heat for this chore.)
Protect Individual Plants – Install hot caps – rigid plastic containers with venting holes – over individual seedlings at planting time. Hot caps act like cloches (mini greenhouses), but venting holes eliminate the daily chore of placing and removing the covering. Create the equivalent of a hot cap using plastic two-liter bottles or gallon jugs with bottoms cut off and lids removed (but saved). Replace lids at night when cold temperatures swoop through.
A twist on the hot cap idea is a Wall O’Water tepee, which encircles individual plants with a sleeve of water-filled tubes. The water absorbs the sun’s heat during the day. At night, as the water slowly freezes, it releases the stored radiant heat of the sun, keeping air inside the tepee frost-free.
How to protect blooming trees from hard-freeze
Q. My peach tree is in full bloom and I just saw a weather report that hard frosts are expected next week. Will this damage my tree?
A. You are not alone. Many of our trees here at the college are in full bloom as well.
The 70-degree weather we had in January fooled many of the trees into thinking it was spring. It is not uncommon for us to get a killing frost while our fruit trees are in bloom. In the Redding area we can have hard frosts well into April and even later in the mountains and surrounding foothills.
Seasoned gardeners can all tell you horror stories about a late frost leveling their spring plantings. This is why early blooming trees, such as cherry and apricots, are unreliable producers of fruit in our area.
What is unusual about this year is that trees are blooming so early and we could easily have another couple of months were temperatures can get well below freezing. The freezing temperatures will defiantly damage the flowers on the tree and any potential fruit production for this year will be lost.
If the temperatures are low enough it may also cause damage to the leaf buds and branches as the tree is no longer dormant.
To protect the trees from the cold there are several things you can try depending on the number of trees you have, their size, location, and the severity and length of below-freezing temperatures.
You can build tripods out of light lumber or PVC pipe around each tree and cover them with frost cloth, blankets or tarps. I have used the same structure I use to support my bird netting to cover my tree with an old tarp. Do not use plastic or sheets as they do not provide enough insulation.
Another option is to hang the trees with the old-fashioned Christmas lights, however these are getting harder to find. They need to be the big bulb type, the newer LED Christmas-tree lights won’t work since they’re cool burning and won’t give off sufficient heat. You can improve the protection by also covering with a blanket or tarp.
Another option is to turn a sprinkler on your trees just as the freeze begins, to coat them with ice. Although it seems counterintuitive, the ice will protect the tree because the temperature beneath the ice will not drop below 32 degrees. For this method to work you will need to keep the sprinkler on until the temperatures rise above freezing. If you plan to use this method of frost protection and the cold temperatures last for a while, monitor to ensure that you are not creating a flood somewhere else.
You may have noticed that some of the big orchards and vineyards use big fans to create air turbulence to protect trees from freezing. I do not like to recommend use of the fan for residential yards for a couple of reasons. First, most of you do not have a large enough fan to create enough air turbulence to be effective in protecting the tree. And if you do just happen to have a giant fan at your disposal you can cause increased damage to surrounding areas by moving the cold air into neighbor’s yard.
The Shasta Master Gardeners Program can be reached by phone at 242-2219 or email [email protected] The gardener office is staffed by volunteers trained by the University of California to answer gardeners’ questions using information based on scientific research.
How to Keep Plants from Freezing in Vegetable Gardens
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Fall can be death to gardens if you don’t know how to keep plants from freezing. Follow these easy methods to extend your harvest.
In the grocery store, you hear those ominous words: “There’s cold weather coming. Have you covered your garden?” You return home and check the weather app to confirm the terrible truth. Temperatures will drop below freezing for a few days. Winter may not be here yet, but a single frosty night can do massive damage to gardens.
Knowing how to keep plants from freezing doesn’t require much research or ingenuity. There are many methods and options, so choose which works best for your garden.
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First of all, what are you growing? If you’re trying to keep tomatoes alive a few more weeks so they all ripen, you don’t need to do more than toss a couple old sheets over the cages. Pots of basil need to come inside. Austrian winter peas will be just fine.
Second, how long are you growing it? Hoops and low tunnels are effective ways to keep gardening all the way through the winter, but they’re insufficient for mature tomato plants. They also require unnecessary labor simply to ripen end-of-season fruit. Hoop houses and cold frame gardening help cultivate vegetables during the winter but they’re best for short and frost-tolerant crops like spinach.
Photo by Shelley DeDauw
How to Keep Plants from Freezing: A List from Least to Greatest
Bring Them Inside: Sounds pretty simple, right? If it’s cold outside, move plants where it’s warmer. The problem is this only works with container gardening. Planning ahead and keeping basil in pots helps when temperatures drop since basil will die even before frost falls.
Temporary Covers: A few frosty nights won’t kill eggplants if they’re protected. And often, temperatures drop for two or three days then rise for another six weeks, giving you time for a full harvest. Run outside before dark and cover your plants. Upend buckets or bowls over short crops, toss sheets over larger plants. The important thing is to keep frost from descending down onto the foliage. But should you use tarps or blankets? Using fabric is best because, if plastic touches the plant, frost will come through the plastic anyway. Plastic must be propped or suspended above crops so there is a protective cushion of air.
But temporary covers are just that: temporary. Most materials don’t allow enough light to shine through. Remove them during the day and replace them at night, so vegetables continue to grow.
Photo by Shelley DeDauw
Cloches: A bell-shaped cover, “cloche” can refer to hats, coverings for serving platters, or glass domes set over plants. The garden-variety cloche protects sensitive seedlings from the cold or forces them to sprout by raising ambient temperatures. Keep the glass variety for displaying knickknacks and make unbreakable, temporary cloches from plastic bottles.
Keep milk jugs or clear 2-liter soft drink bottles. Cut off the bottoms but leave lids intact. Fit these over seedlings and small plants. At night, keep lids on. But if weather warms, remove the lids to allow airflow to developing plants. Remove cloches when the danger of frost has passed or when the plant surpasses the available size.
Other cloche-type products include “plant protectors” or “frost covers,” fabric- or plastic-covered wire frames designed to fit directly atop single plants during inclement weather. These are available through most gardening supply stores, though they cost much more than erecting a wire frame and fitting plastic over top.
Photo by Shelley DeDauw
Frost Blanket: A valuable breakthrough in horticulture technology, a frost blanket allows a high percentage of sunlight to come through the fabric while protecting plants beneath from cold. Some frost blankets protect to 5°F while others go past 15°F; generally, more protective products cost more. Handled gently, this material can last for years. Some gardeners even keep it on during the summer to act as an insect or pollen barrier.
Lightweight and gauzy, a frost blanket can easily blow off in a storm. But instead of purchasing clips made specifically for tacking the material down, look for binder clips sold within office supplies departments. Smaller binder clips secure cloth to tomato cages while larger clips grip fence boards. Combine a frost blanket with wire or PVC to make low tunnels.
Work with Nature: Though the air may get frosty, vegetables within the earth stay cool and comfortable until it’s cold enough for even the soil to freeze. In fact, this is an ancient way of how to store vegetables in winter. With the exception of sweet potatoes and other tropical tubers, root vegetables prefer cooler environments. They won’t die if the soil doesn’t actually freeze. To add protection, pack straw or leaf mulch around the exposed plant tops. The tops may die but vegetables beneath are fine. Brush mulch back then pull or dig vegetables when you need them.
Photo by Shelley DeDauw
Low Tunnels/Hoop Houses: Too fussy and labor-intensive for overnight protection, these structures are intended to warm crops for weeks to months. Insulating material, usually plastic, stretches over domes made of wire, PVC, or wood. And they come in different sizes. Low tunnels range from a foot to several feet high; gardeners must pull plastic back to tend small crops within. Hoop houses can be small enough to protect a single garden bed or rise seven feet high and extend 50 feet in length. When they are that large, and used for commercial production, they are often called high tunnels. And the shortest and longest structures, caterpillar tunnels, sometimes exist within high tunnels when external temperatures drop so low the plants need two layers of protection. How much protection each house provides depends on the size of the house and how full it is; fuller houses stay warmer.
Garden hoops purchased through seed companies are often so flimsy they will fly away in a stiff wind and rarely last longer than one season. Gardeners within colder regions often construct raised beds with rings and grommets in the corners, ready to receive PVC poles when plants must be covered. And the large high tunnels, sturdy and covered with high-grade plastic, save thousands over rigid greenhouses providing the same growing space.
To ensure protection within hoop houses, keep plants away from plastic walls. Provide supplementary heat during hard frosts and remember houses which are full of plants stay warmer than emptier spaces.
Cold Frames: Solid and permanent structures, cold frames are garden boxes built so glass panes can sit on top. This provides an environment in which short vegetables can grow through even the coldest temperatures. Innovative cold frames are built of wooden planks then topped with glass-paned doors on hinges, so the gardeners can lift the doors to access lettuce inside. Construct cheaper and more temporary cold frames by placing straw bales at the perimeter of a small garden bed then placing a discarded shower door overtop when temperatures drop.
Insulate with Water: And if hoop houses or cold frames aren’t enough? This often happens when a hard frost blows in, threatening tender tomato seedlings in low tunnels which have no supplementary heat. Water is an excellent insulator. Place full water jugs beside plants during the day. They draw in heat as the sun shines then, at night, release it back out. Collect enough jugs to place as close as possible to each plant you need to protect.
Photo by Shelley DeDauw
Supplementary Heat: Dedicated winter gardeners know how cold it can get, and they’re determined to protect the plants. Running a heavy-duty, weather-resistant extension cord out to a hoop house can keep the most sensitive plants cozy during a rough night.
Christmas lights, the safest and prettiest option, emit enough heat to add 2-10°F to the environment. Line low tunnels with light strands, boosting that high-quality frost blanket’s protection value. LED lights, the safest, provide the least heat. Old-fashioned miniature bulbs get warm to the touch; larger C7 and C9 bulbs emit the most heat but can be a fire hazard so they must be kept away from flammable materials.
Heat tape, often used for seed sprouting, warms soil. Place this beneath trays of peat pellets so germination doesn’t slow during a cold spring night. Or line soil used for root vegetables to keep the dirt from freezing.
With bulbs ranging from 50 watts for pet use to over 250 watts, heat lamps can provide a little or a lot of protection. They are valuable when placed within a plastic hoop house, since most heat created stays within the structure. When using heat bulbs, remember heat rises up, so clipping a lamp to the top beams doesn’t help as much as keeping the lamp low. They are also very flammable. Do not use them near anything which may ignite and keep all plastic or frost blankets within a safe distance.
Space heaters provide the most warmth. They also have flaws. Radiant units focus heat at one specific area, which may overheat while the space behind the heater stays cold. Forced air heaters circulate warmth around the hoop house but the air can be drying; gardeners must monitor plants and soil more carefully to ensure nothing dries out. Place heaters down low, since heat rises up. Keep plants out of the immediate path to avoid damage. And always use a heavy-duty outdoor extension cord! Cheaper cords will short out or fail, causing damage to plants or structures.
Greenhouses: These houses are rigid, with walls made of glass or clear acrylic. Though they are often confused with hoop houses, gardeners consider greenhouses to be permanent, often with built-in heating and ventilation systems. This makes greenhouses much more expensive than hoop houses. Dedicated gardeners may tire of repairing and replacing plastic on high tunnels damaged by animals and strong winds, choosing to invest in greenhouses; others figure it’ll take too long to earn back the investment. But the benefits of these structures are immense: the highest-quality houses can protect banana trees in Alaska.
Knowing and Planning How to Keep Plants from Freezing
Don’t wait until that first frost comes in. Research your garden zone in anticipation for colder weather then purchase a few items.
Focus on materials which can be used year after year. Spending more on a higher-quality frost blanket, or a longer roll, means you don’t have to purchase it again next year. But forego the accessories if you can instead find binder clips at the dollar store then use old, bent tomato cages to support the cloth. Frequent clearance sales after the holidays to acquire strands of outdoor Christmas lights. Purchase old sheets at yard sales. Keep five-gallon buckets stacked within a garage so you can run out and protect plants in just a few minutes.
Plan where you will put your crops. Within colder regions, it may benefit you to keep basil and rosemary within pots so you can tote them inside. Pay attention to surrounding landmarks such as wooden fences, brick walls, or overhanging trees; blankets can easily be tacked to fences, brick walls retain and reflect heat, and overhanging trees can catch frost before it falls on tomatoes.
Also, ask experienced gardeners about weather patterns within your area. Cheap low tunnels can rip up and blow away in a stiff wind but PVC, inserted into grommets bolted onto raised beds, will survive if the fabric is secured well enough. Frost blanket can collapse in the same heavy snow which will slide off plastic.
Research how to keep plants from freezing so you are prepared when it happens. A little extra work can prolong your harvest for a long time.
Do you have any tips on how to keep plants from freezing? Please let us know!
|Method||How to Use||Protection Provided|
|Bring Plants Inside||Plant sensitive crops within
containers so they can be
carried into the house.
|100% protection, if plants
|Temporary Covers||Cover individual plants with
buckets, newspaper, blankets,
|Frost protection only. Will not protect
foliage where plastic touches.
|Cloches||Cut bottoms from clear milk
jugs or 2-liter bottles. Set over
plants. Remove caps during warm
days but replace at night.
|Frost and up to 4°F. Cover
cloches with additional items such
as buckets during hard frosts.
|Frost Blanket||Drape over crops. Clip or tack down.||Frost and 2-10°F, depending on
cloth quality and how well it is secured.
|Work with Nature||Keep root crops in the ground.
Cover ground with heavy mulch.
|Will usually keep roots from freezing
in temperatures above 15°F if enough
mulch is applied.
|Arch wire or PVC over beds. Cover
with plastic or frost blanket. Secure
material using strong clips or anchors.
|Frost and up to 10°F without
supplementary heat. Protection
varies based on size, materials used,
and how many plants reside inside.
|Cold Frames||Surround beds with straw bales or
wood. Place old windows or shower
doors on top.
|Frost and up to 10°F without
supplementary heat. Best used to
extend seasons for cold weather crops.
|Water Jugs||Fill capped jugs with water. Place
beside plants during the day and
keep them there at night. Use in
conjunction with frost blanket or
|Adds 2-5°F more protection to
plants in close proximity. Will not protect
plants which do not also have overhead
|Christmas Lights||Wind strands with mini bulbs around
plants or hang C7/C9 strands from
supports. Use in conjunction with frost
blanket or tunnels. Observe safety
|Up to 10°F additional protection,
depending on type of light used. Will
add little protection to plants which do
not also have overhead frost protection.
|Heat Tape||Place beneath containers used for
germinating seeds. Place along soil
used for root vegetables.
|Up to 5°F additional protection.
Useful only for warming soil.
|Heat Bulbs||Place low within hoop houses. Keep
plants away from direct beam.
Observe safety precautions.
|5-20 degrees additional protection,
depending on bulb wattage, hoop house/
greenhouse size and construction, and
number of plants placed within house.
|Space Heaters||Place low within hoop houses. Keep
plants away from direct heat produced
by elements or fans. Observe safety
precautions. Always use heavy duty
outdoor extension cords.
|5-30°F additional protection,
depending on strength of heater, size
and structure of hoop house/greenhouse,
and number of plants placed within house.
Protect Your Plants In A Freeze – How To Protect Plants From Freezing
Gardeners plant flowers, shrubs and trees that can survive in their garden during typical weather. But what can a gardener do when the weather is anything but typical? Unexpected freezes can devastate landscapes and gardens. It can leave a gardener wondering how to protect plants from freezing and what is the best way to cover and keep plants from freezing.
At What Temperature Do Plants Freeze?
When cold weather comes your way, your first thought will be at what temperature do plants freeze, in other words, how cold is too cold? There is no easy answer to this.
Different plants freeze and die at different temperatures. That is why they are given a hardiness rating. Some plants produce special hormones that keep them from freezing, and these plants have a lower hardiness rating (meaning they can survive colder weather) than plants who produce less of this hormone.
That being said, there is also different definitions of survival. A plant may lose all of its foliage during a freeze and the plant can regrow from the stems or even the roots. So, while the leaves cannot survive a certain temperature, other parts of the plant can.
How to Protect Plants from Freezing
If you are only expecting a light freeze, you may be able to protect plants in a freeze simply by covering them with a sheet or a blanket. This acts like insulation, keeping warm air from the ground around the plant. The warmth may be enough to keep a plant from freezing during a short cold snap.
For added protection when you protect plants in a freeze, you can place plastic over the sheets or blankets to help keep warmth in. Never cover a plant with just plastic, however, as the plastic will damage the plant. Make sure that a cloth barrier is between the plastic and the plant.
Be sure to remove the sheets and blanket and plastic first thing in the morning after an overnight cold snap. If you do not do so, condensation can build up and freeze again under the covering, which will damage the plant.
When protecting plants in a freeze that is longer or deeper, you may have no choice but to expect to sacrifice all or part of the plant in hopes that the roots will survive. Start by heavily mulching the roots of the plant with either wood mulch or hay. For added protection, you can nestle gallon jugs of warm water into the mulch each night. This will help drive off some of the cold that can kill the roots.
If you have time before a freeze happens, you can also create insulation barriers around a plant as a way how to protect plants from freezing. Tie up the plant as neatly as possible. Drive stakes that are as tall as the plant into the ground around the plant. Wrap the stakes in burlap so that the plant appears to be fenced in. Stuff the inside of this fence with hay or leaves. Again, you can place milk jugs of warm water on the inside, at the base of this fence each night to help supplement the heat. A string of Christmas lights wrapped around the plant can also help add additional heat. As soon as the freeze passes, remove the covering so that the plant can get the sunlight it needs.
Watering the soil (not the leaves or stems of the plants) will also help the soil retain heat and can help the plant’s roots and lower branches survive.
Protect Your Plants from Frost Damage
Frost damages many plants and may even kill them, therefore steps to minimise damage need to be a consideration for every garden or plantation.
Most of Victoria is liable to frost at some time of the year. Areas along the Great Divide and the adjacent slopes are amongst the most frost-prone parts of Australia.
Local knowledge is important in planning for frost because features of the landscape such as valleys and hills can channel or divert cold air as it flows downhill, creating microclimates which are significantly more or less frost-prone than the surrounding region.
♦ Frost damage occurs when plant tissue is frozen. Freezing causes the plant’s cells to shrink, forcing water into spaces between the cells where it can freeze and form ice crystals. As temperatures rise and thawing begins the water is absorbed back into the cells by osmosis. If this occurs quickly there is no damage to the tissue, but if thawing is slow, the cells are deprived of water and become dehydrated resulting in ‘frost burn’.
♦ Frost damage can also occur in times of rapid thawing when frozen foliage receives strong sunshine.
♦ Frequent low night temperatures in autumn help to harden stems and foliage, reducing the likelihood of frost damage.
♦ Severe frost damage is more likely to occur in late winter and spring when new foliage is appearing:
♦ Light frost: down to about -2 to -3°C. Foliar damage may occur on some plants.
♦ Moderate frost: down to about -4 to -5°C. The next major damage point.
♦ Heavy frost: beyond about -6°C. The next group of plants susceptible to cold damage is affected.
How to Minimise Frost Damage
Cultivate frost-tolerant plants
This is an aspect of gardening that is difficult to adhere to. Gardeners may not want to understand or believe that some of the plants in their garden are not suitable for the local climate. They are mesmerised by some attribute of foliage, flower, or form which makes a plant a ‘must have’, and become oblivious to the pressure it will be put under by low temperatures.
>> Select a Frost-tolerant Plant from our list of recommended plants.
Take advantage of microclimates
The number of microclimates even on a suburban property can be surprising. Well-developed tree canopies can be valuable for affording frost-protection. Observe which areas on the property are free of frost pockets. This is where tender plants should be grown.
No nitrogenous fertilisers after midsummer
In frost-prone areas it is recommended that nitrogenous fertilisers should not be applied to plants after midsummer because they promote foliar growth.
Avoid blocking air flow
Organise plantings so that they do not block the flow of cold air at or near ground level, because wherever airflow is curtailed is where the greatest area of frost will occur. Avoid anything that may form an ‘air dam’, such as a build-up of weeds around plants, hedges, fences, buildings, etc.
Keep soils moist
Dryness is an ally of frost.
Mulch with gravel or screenings
Avoid organic mulches because they have plenty of spaces to act as ‘air dams’ where frost can occur.
Avoid recently cultivated soil near plants
Recently cultivated soil contributes to frost damage as there are many nooks, crannies, and depressions where cold air can be trapped. This aspect is understood by orchardists and viticulturalists who, in late winter and early spring, roll the soil flat in close proximity to their trees and vines.
No winter / spring pruning
Do not prune in winter or spring until frosts are thought to be finished for the season. As sap flow increases and young leaves begin to burst forth this is a perfect time for frost damage to occur.
Provide overhead protection, using hessian, to help retain radiant heat near the plants. Do not cover plants with plastic bags as they do not always exclude frost, and can exacerbate damage if hit by strong sunlight early in the day after a frosty night.
Spray with seaweed products
Spray applications of seaweed products help to strengthen cell walls, minimising the chance of frost damage and also helping the plant cope with excessive heat.
Based on an article by Rodger Elliot
Here are tips on how to protect your garden from frost and design a garden to reduce frost damage—plus, a handy chart listing dangerous temperature lows for vegetables.
To know when your area gets frost, see our U.S. Frost Dates Calculator and the Canadian Frost Dates.
Whether you are waiting to plant in spring or those late fall days are getting frosty, it is important that frosts will not hamper your efforts.
When to Protect Your Plans
If temperatures below 32 degrees F are predicted, protect your plants! A moderate freeze with temperatures in the 25- to 28-degree Fahrenheit range can be widely destructive to vegetation.
Frost protection is especially important for tender plants such as geraniums, begonias, impatiens, peppers, and tomatoes.
- In the spring, use row covers if you have tender vegetable seedlings and transplants in the spring. Row covers or garden fleece can also be used to help create a warmer environment beneath them. You’ll need to use posts or bamboo to create space for the plants to grow, then drape landscape fabric or plastic over the posts; weigh down the edges with rocks or bricks or pegs so the covers do not blow away.
- Alternatively, you can recycle clear plastic drinks bottles as plant covers or “cloches.” Simply cut a bottle in half using sharp scissors, then place the top half over your plant. Keep the lid off on sunny days, or screw it on when cold weather is forecast. Keep your bottle cloches from blowing away by pushing them into the soil or by holding them in place with a cane.
- Cover other established plants with frost cloths or other insulators including newspapers, straw, old sheets and bedspreads, or evergreen branches. Cover the whole plant; you’re trying to retain radiated heat.
- It’s best to have all covers in place well before sunset. Drape loosely to allow for air circulation. Before you cover the plants in late afternoon or early evening, water your plants lightly.
- The plants should be mulched, but pull the mulch back from the root of the plants.
- Remove the covers by mid-morning.
- In the fall, the first frost is often followed by a prolonged period of frost-free weather. Cover tender flowers and vegetables on frosty nights, and you may be able to enjoy extra weeks of gardening.
What Temperatures Cause Frost Damage?
Designing Your Garden to Reduce Frost
Here are different ways through which you can reduce the amount of cooling in and around your garden.
- Your garden will warm up more during the day if it slopes toward the sun. Residual heat in plants and soil may determine whether your garden sustains frost damage during the night. Cold air, which is dense and heavy, will flow away from plants growing on a slope—what the experts call “drainage.”
- A garden on a south-facing slope offers two advantages: more exposure to the Sun, and better drainage of cold air. In deep valleys, nighttime temperatures may be as much as 18°F lower than the temperature on the surrounding hills.
- Trees surrounding your garden act like a blanket and reduce the amount of heat radiating from the soil, perhaps keeping the temperature high enough to protect your plants from early fall frosts. Plants themselves can modify cooling. Place plants close together to create a canopy that entraps heat from the soil (though the tops can still suffer frost damage).
- A garden wall benefits the garden by acting as a heat sink, absorbing warmth from the Sun during the day and radiating it slowly at night.
- Water in a nearby lake or pond (if it is one acre or larger) will also act as a heat sink. A cold frame can be heated with an improvised heat sink: a dozen 1-gallon jugs of water. They absorb heat during the day and radiate it at night.
- Moisture also determines whether frost will nip your tomatoes. Condensation warms and evaporation cools. When moisture in the air condenses on plants and soil, heat is produced, sometimes raising the temperature enough to save the plants. On the other hand, if the air is dry, moisture in the soil will evaporate, removing some heat.
- Good soil, full of organic matter, retains moisture, reducing the rate of evaporation. Mulch also helps to prevent evaporation.
- In early spring, warm up your soil faster by covering it over with plastic, row covers or garden fleece. This technique is particularly useful for heavy or clay soils that retain a lot of moisture. Lay the plastic over the ground at least one week before sowing and soil temperatures will rise by a couple of degrees, making all the difference for early sowings.
- Of course, raised beds will warm up more quickly thanks to the free-draining conditions within them, so if you have raised beds, start your first sowings here.
Design your garden with the Almanac Garden Planner which uses averaged frost data from nearly 5,000 weather stations across the U.S. and Canada. To benefit from this, consider a free 7-day trial to our Almanac Garden Planner!
When the sky seems very full of stars, expect frost. –Weather Lore
If it has been a glorious day, with a clear sky and low humidity, chances are that temperatures will drop enough at night to cause frost.
Find out how to predict that a frost is coming!
See our Autumnal Equinox page for more fall-themed advice, folklore, facts, and fun!
How to Save a Cold-Damaged Plant
Although many parts of the country are under a deep freeze during this time of year, other areas experience more temperate winter temperatures. Of course, that doesn’t mean that those areas can’t also experience a frost or frozen conditions every now and then. While on average, temperatures may not dip much below 40 degrees Fahrenheit in these regions, a cold snap can sometimes drive temperatures into the 20s — much to the surprise of your cold-sensitive plants. Some plants can handle cold temperatures with minimal stress. Unfortunately, others can be seriously impacted by the cold, whether it comes in the form of a light frost or a hard freeze. In general, hard freezes tend to cause the most damage. What can you do to help your plants repair themselves?
Much like overprotective parents, gardeners may panic when they notice a coat of frost on their plants. While it may be tempting to fuss over them right away, it’s best to leave them alone for a bit — or at least until new growth appears and you can fully assess the damage.
Don’t Encourage the Plant to Grow Just Yet
While the plant will eventually grow on its own, you’ll want to resist the urge to encourage new growth by applying more fertilizer. Sure, you may want to give it a nutrient boost to help it repair itself, but doing so will only prompt it to send out new growth, which could be even more negatively impacted in the event of another cold snap.
It may seem counterintuitive, but it’s actually best to water your cold-shocked plants. Water will help them recover from the trauma and stress. Give your damaged plants about an inch of water or so. When plants experience a freeze, moisture is removed from their tissues. Watering them afterwards allows them to rehydrate.
Put Away Those Clippers (For Now)
It can also be tempting to remove the damaged leaves and shoots from your plants. However, pruning may only stress them further. Wait until the weather warms up to cut the damaged parts off (or, if you brought the plants inside for the winter, wait about a month). If the plant is a woody variety, you’ll want to assess the damage later in the winter. Simply scratch the bark and look at the color of the material underneath. If it’s green, the plant is still alive and will have a chance to grow again. For the time being, just clean up any dried or dead leaves that fall off your plants.
Bring Your Potted Plants Indoors
If any of your tropical plants were impacted by a frost, you should bring them inside and set them on an enclosed porch or deck (or put them in your garage). Avoid placing them in a room that’s too warm, as that will also cause shock. Leave them indoors away from direct sunlight, and continue to water them periodically, assessing any damage you see as you go. Typically, the dead bits will fall off over time. If you have to leave your container plants outside, at least huddle them together so they can use one another for warmth.
If You Have Succulents, Handle Them With Care
Since succulents and cacti store water in their stems and bodies, they’re more susceptible to serious damage at the cellular level if they experience a freeze. The good news is that many of these plants are super hardy, so you may just need to remove damaged foliage from them. Wait a few days and assess the plants — if their interiors are mushy or black, they probably aren’t salvageable. However, if you spot new growth, they’ll most likely survive.
Assess the Damage
In the event of a light freeze, a plant’s foliage may be damaged or discolored. If this is the case with your plants, it’s best to wait for those damaged bits to fall off on their own. If the frost is more severe, it may impact the plants’ roots and crowns. When this occurs, the damage has probably reached the cellular level, which means it might permanently affect the tissue. While the plants may recover in time, there’s also a chance that they may not. However, you should still give them several months just to be sure.
Over time, the impacted plants will recover, especially if they are native to your area. Since they are used to weather fluctuations in your area, they can typically withstand the occasional cold snap. Other plants will take more time to heal. Give them several months to recover, thoroughly assessing the damage and looking for new growth before throwing them in the compost bin.
How to Avoid Damage in the Future
Cover sensitive plants to protect them from the cold. If a frost is in the forecast, cover them with a special plastic plant cover, bedsheets, burlap sacks, or even inverted plastic containers. Place the covers over your plants overnight and remove them in the morning.
Move tropical plants indoors. If you live in an area that gets sporadic cold snaps during the winter, bring your plants inside, or at least put them under a covered porch/deck. If temperatures are expected to drop dramatically, place them indoors in a garage or sunroom.
Cultivate cold-hardy plants that can survive the temperature fluctuations in your area. Better yet, plant native plants that have evolved to grow in your region and have a better chance of surviving colder weather. If you’ve moved and you can’t bear to part with your warmer, more tropical plants, place them in a heated greenhouse or indoors near a window.