How to Keep Plants from Freezing in Vegetable Gardens

Techniques and Plant Covers for Winter Gardening

How to Keep Plants from Freezing in Vegetable Gardens

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.

how-to-keep-plants-from-freezing
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.

how-to-keep-plants-from-freezing
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.

how-to-keep-plants-from-freezing
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.

how-to-keep-plants-from-freezing
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.

how-to-keep-plants-from-freezing
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
are portable.
Temporary Covers Cover individual plants with
buckets, newspaper, blankets,
or tarps.
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.
Low Tunnels/
Hoop Houses
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
tunnels.
Adds 2-5°F more protection to
plants in close proximity. Will not protect
plants which do not also have overhead
frost protection.
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
precautions.
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.

 

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