Protecting Your Garden From Frost

Frost Dates

First, know approximately when your location typically gets frost. See our Frost Dates Calculator for local average frost dates in spring and fall.

• Note: On weather sites, many frost dates are based on a 50% chance of frost. However, our calculator assumes a 30% probability of frost. After all, do you want a 50% chance of your plant dying?

Second, know that a light frost—32°F and colder—kills all tender plants such as tomatoes. Hardier plants such as spinach and kale will survive until there’s a hard freeze—28°F and colder. (We explain the frost tolerance level of different crops below.)

As gardeners, our frost dates are based on 32 degrees Fahrenheit (0 degrees Celsius) to avoid the risk of any plant death. However, know that even if air temperatures are as high as 38°F, frosts may occur on the ground and on plants. It’s better to protect plants just in case!

Weather Forecast

Of course, frost dates are only a general guide. They are not predicting the upcoming year’s frost; rather, they are averages based on multiple years of historical data. Plus, frost dates are based on the nearest reporting weather station; they don’t reflect smaller “microclimates” in your yard such as a low spot or an area near water or pavement. 

So, keep a close eye on the daily weather forecast! If it looks like temperatures are going to drop, get ready to protect tender plants. Moisture also determines whether frost will nip your plants. 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. 

Also, the first frosts of the season usually happen on clear, calm nights.  

What Temperatures Cause Frost Damage?

Frost causes damage and even failure to many vegetable crops. But some crops will taste even better with frost. The flavor of broccoli, for instance, actually improves if the plant has experienced a frost, and carrots get sweeter as the temperature drops. Root crops develop more sugars when the soil temperature is below 40° F; and Brussels sprouts are often best after a light freeze.

How low can you go? The temperatures shown in the graphic below tell you when the frost will cause damage to the respective vegetable.

Frost Resistance of Vegetables

Another way gardeners look at frost resistance is to categorize from “hardy” to “tender.” Some plants (“hardy”) tolerate some amount of short-term freezing, while other plants (“tender”) are killed or injured by freezing temperatures.

Hardy Vegetables (Frost hardy; below 28° F):

Can withstand freezing temperatures and hard frosts for short periods without injury.
Broccoli
Brussels sprouts
Cabbage
Collards
Horseradish
Kale
Kohlrabi
Mustard Greens
Onion (sets and seeds)
Parsley
Peas
Radish
Rutabaga
Spinach
Turnips

Frost-Tolerant Vegetables (can withstand light frost; 28 to 32° F):

Beet
Carrot
Cauliflower
Celery
Chard
Chinese Cabbage
Endive
Jerusalem artichoke
Lettuce
Onion, garlic, chives
Parsnips
Potatoes
Rhubarb

Tender Vegetables (No frost)

The following vegetables are damaged by light frost. They should be protected from frost or harvested before frost.
Beans
Cucumber
Eggplant
Muskmelon
Okra
Pepper
Pumpkin
Squash, summer
Squash, winter
Sweet corn
Sweet potato
Tomato
Watermelon

Notes:

• Pumpkins and winter squash may be able to tolerate very light frosts, but it is better to protect them if possible.
• Tomatoes can be harvested and will ripen off the vine; they must be at least “mature green” (changed from the deep green to almost turning red)
• Muskmelons must “slip” easily from the vine to to ripen further at room temperatures.

How to Protect Plants from Frost

Of course, the main way to protect plants from frosts is to cover them with a blanket or row cover. This material traps the heat to keep plants warmer.  It’s worth the time to cover your crops because sometimes an early freeze is a freak incident and there are many days of great weather to follow.

• Row covers are made of non-woven polyester. Garden stores will sell “row covers” of different weights or thickness.
• Bed sheets, drop cloths, or medium-weight fabric will also make suitable covers for vulnerable plants. Do not use plastic. 
• Drape loosely to allow for air circulation. Do not let the material rest on the plants.
• Secure to ground with rocks or bricks or stakes to keep the covering from touching the foliage beneath.
• Keep sheets or row covers at the ready, stored somewhere dry, neatly rolled up and off the ground to keep them away from vermin. If you use polythene covers, hose them down if they’re dirty and dry them so they’re ready to use when frost threatens. It’s best to have all covers in place well before sunset. Before you cover the plants in late afternoon or early evening, water your plants lightly. 
• Apply covers in early evening as winds die down, and remove the coverings when temperatures rise the next day (mid-morning) so that plants can get full exposure to the warming sunlight.

For a few smaller plants you can make “hot caps” from recycled milk or soda bottles with the bottoms cut out, paper bags, or newspaper tents. For example, just cut a 2-liter clear plastic soda bottle in half.

Mulch Low Plantings

For a short cold period, low plantings can be covered with mulch, such as straw or leaf mold. Remove once the danger of frost has passed. Read more about using mulch.

Create Cold Frames

In the future, consider cold frames for your garden, either portable or permanent. Here’s how to make cold frames.

Or, make a mini-hoop house using homemade hoops of PVC water pipe, slid onto lengths of rebar hammered into the ground. Connect the hoops at the top with a central ridge of piping. It’s an effective way to keep winter hardy salads and vegetables safe from harsh weather. See how to make a row cover tunnel. 

Employ Irrigation

Moist soil can hold up to four times more heat than a dry soil, conducting heat faster to the soil surface, and keeping the air above it about five degrees (F) warmer. So water well before a frost. A variation on this water theme is milk jugs, painted black, full of water in the garden. These absorb heat during the day, releasing it at night.

Protect Root Crops

 In milder regions, they root crops can be left in the ground. Some, like parsnips, actually become sweeter after a frost. Mulch your root vegetables with a thick layer of compost, straw, dried leaves or leaf mold, but if the ground is likely to freeze solid for a long period, dig them up and store them somewhere cool, dry and frost-free. 

Protect Containers

In winter the biggest enemy of crops in pots is persistently wet potting soil. Make sure there is adequate drainage by placing containers onto pot feet (or improvise with small rocks).  Some containers can crack in very cold conditions. To prevent this, wrap pots in bubble plastic or burlap. Move pots somewhere more sheltered if possible, for instance against a South-facing house wall, or into a greenhouse. 

Protect Soil in Winter

Don’t forget about the soil! Keep soil covered to protect beneficial soil life such as worm-, bug- and fungi-happy.  Before it gets too cold, add a thick layer of organic matter to the surface to keep soil life fed and protect the soil itself from erosion. 

VIDEO: How To Protect Plants

See how to protect your garden with some of these techniques.

Fall Frost Tips

If you’re a gardener, it’s the first fall frost which is most concerning, as it can result in a lot of lost crops. Here are a few more fall frost damage prevention tips:

• Water the soil thoroughly before frost. Water holds heat better than dry soil, protecting roots and warming air near the soil. However, avoid soaking the ground as this can lead to the water freezing within the soil and damaging the roots.
• 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. 
• Mulch your garden beds. Mulching with materials like straw, pine needles and wood chips helps preserve heat and moisture and so prevents frosts forming.

In fall, protecting tender plants and harvesting crops before frost hits are most important. Before a light frost:

• Bring houseplants (especially tropicals) and other tender plants indoors before the first light frost arrives. Keep them in a sunny window in a relatively moist room; the kitchen is often best.
• Harvest basil and other tender herbs. Even if they survive the frost, they don’t do well in cold temperatures. The same is true for most annuals.
• Harvest all tender vegetables and tender greens, including: tomatoes, eggplants, peppers, beans, cucumbers, watermelons, cantaloupe, okra, squash, and sweet corn. Green tomatoes don’t need light to ripen, and in fact ripening can be slowed by light.  Keep fruit 55 and 65 degrees (F) for best ripening. Here are a few tips for ripening green tomatoes.

For plants that can survive a light frost, add a heavy layer of mulch to keep the ground around them from freezing. You can still harvest late into the fall as long as the ground isn’t frozen. These veggies include: beets, broccoli, cabbage, celery, lettuce, parsnips, arugula, swiss chard, and other leafy greens.

Wait to harvest plants that can survive a hard frost last, such as: carrots, garlic, horseradish, kale, rutabagas, leeks, parsnips, radishes, spinach, and turnips.

Spring Frost Tips

Here are some extra tips for preventing frost damage in spring. It can be a real bummer to lose young plants to a late spring frost.

• In early spring, warm up your soil faster by covering it over with row covers or garden fleece. This technique is particularly useful for heavy or clay soils that retain a lot of moisture. Lay the material 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.
• While frosts are still possible, plant cool-season crops that are more tolerant of colder temperatures. Crops like peas, spinach, kale, and cabbage can power through a light spring frost.
• Start tender or warm-season crops—like tomatoes and peppers—indoors or after the threat of frost has passed. Consult our Planting Calendar to see recommended planting dates.

Designing Your Garden to Reduce Frost Damage

A garden designed with frost in mind can help to mitigate the extent of cold damage experienced by your plants. Here are a selection of different ways that you can reduce the amount of cooling in and around your garden:

Consider Garden Placement

• 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.
• Avoid planting tender species in open, exposed areas or in low spots where cold air settles. Better to put them near a south or west-facing wall, which absorbs heat during the day and radiates it at night.

Use Nearby Structures as Heat Sinks and Natural Covers

• Fences, boulders and shrubs can serve as protective function for nearby plantings.
• Trees surrounding your garden can act like a blanket and reduce the amount of heat radiating from the soil, potentially keeping the temperature high enough to protect your plants from early fall frosts. Plants themselves can modify cooling, too. Place plants close together to create a canopy that entraps heat from the soil (though the tops can still suffer frost damage).
• A garden positioned in front of a rock or brick wall benefits from the warmth absorbed by the wall during the day. At night, it will radiate heat slowly.
• A body of water (if it is one acre or larger) will also act as a heat sink. Similarly, 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.

Other Design Considerations

• Raised beds will warm up more quickly than in-ground gardens, but may need some extra attention if plants (such as garlic) are left to overwinter.
• Use good soil that’s full of organic matter retains moisture more easily, reducing the rate of evaporation. Mulch also helps to prevent evaporation.

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. Try it out for free here!

Learn How to Predict Frost

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. Read more about how to predict a frost!