I enjoy attempting to grow my own fruits and vegetables in my gardens. However, frost and freezing temperatures can be deadly for certain kinds of plants. When the temperature of the air remains at or above freezing (32º Fahrenheit), most plants will only suffer minor or no damage if the night suddenly turns cool. However, if the temperature drops below freezing, the cells of plants that are not frost hardy may freeze, resulting in the death of the plant. As the weather has turned cold in my neck of the woods, I have again begun thinking about how to protect my plants from the cold. Fortunately, learning how to protect plants from frost and freezing temperatures can be quick and easy with these simple tips and instructions.
Originally published on November 21, 2011. Updated on June 10, 2024.
Frost Hardiness of Plants
Before you should scramble to protect your outdoor plants from freezing temperatures and frost, you should first determine and understand the frost hardiness of each type of plant. Frost hardiness refers to the degrees of different types of frost that a plant can withstand without damage or death to the plant. The four levels of frost hardiness are very hardy plants, hardy plants, half hardy plants, and tender plants. Very hardy plants can be planted up to seven weeks before the last frost, hardy plants up to five weeks before the last front, half hardy plants up to three weeks before the last frost, and tender plants after the last frost. Some of the most popular types of frost hardy plants include the following:
Very Hardy: alyssum, asparagus, carnations, chives, dusty miller, fennel, kale, onions, pansies, peas, potatoes, radishes, snapdragons, strawberries, sweet pea, thyme
Hardy: anemones, baby’s breath, broccoli, Brussels sprouts, cabbage, cauliflower, day lilies, dianthus, English daisies, flax, forget-me-nots, hollyhocks, hostas, lavender, lettuce, mums, painted daisies, poppies, rhubarb, roses, spinach, Swiss chard, violets
Half Hardy: artichokes, celery, cosmos, hibiscus, leeks, peonies, petunias, purple coneflowers, roses
Tender: African daisies, bananas, begonias, black eyes Susans, cannas, cantaloupe, chrysanthemums, cucumbers, dahlias, eggplants, fuchsias, geraniums, heliotropes, impatiens, jasmine, marigolds, morning glories, okra, oleander, peanuts, peppers, periwinkles, pumpkins, sunflowers, squashes, sweet potatoes, tomatoes, watermelons, zinnias
Signs of Frost Damage
Even with all the preventative measures in place, sometimes frost damage can still occur. Recognizing the signs of frost damage so you can take immediate action is important. Look for blackened or wilted leaves, which indicate that the cells inside the plant have frozen and burst. Frost-damaged plants may also appear water-soaked or translucent. If you catch frost damage early, you can often save the plant by moving it to a warmer location or providing extra care to encourage recovery. Prune away the damaged parts, being careful not to remove too much, and give the plant some time to recover before deciding whether it needs to be replaced.
Tips for Frost Protection
Planting at the Right Time
The best way to protect plants from frost and freezing temperatures is to plant at the appropriate time. For example, the typical last frost date in central Illinois is May 15, so a gardener living in this area would plant very hardy plants no earlier than March 27, hardy plants no earlier than April 10, half hardy plants no earlier than April 24, and tender plants after May 15. If you do plant too early or a frost happens later than expected, the best course of action is to cover plants to offer protection against freezing temperatures and frost. Things that you can use to cover your plants include newspaper, cardboard, old blankets or sheets, burlap sacks, and plastic tarps. Cover plants at sunset, and remove coverings first thing in the morning to prevent plants from being crushed or suffocated. If you have potted plants, simply bring these inside for the night instead of covering.
Using Heat
Because air temperature drops faster than ground temperature, you can also prevent frost damage to plants by helping the heat from the earth rise or by keeping the cold from the air away from the plants. To use the heat from the ground to your benefit, water your garden thoroughly at sunset. The soil will release moisture throughout the night, which will warm the air around the plants. However, do not spray water directly on plants because remaining water droplets could freeze. Mulch can also be used to trap heat around plants. To collect heat throughout the day and channel heat towards plants during the night, place plastic buckets or contains around plants. Buckets work especially well for tomato and pepper plants and also help to prevent rabbits and other animals from nibbling at seedlings. If you have a small garden or own many electric fans, you can also set up fans to blow cold air away from plants through the night.
Using Row Covers and Cold Frames
Another effective method for protecting plants from frost is the use of row covers and cold frames. Row covers are made from lightweight, breathable fabric that you can drape directly over plants. They provide a few degrees of frost protection by trapping the heat from the earth, and they are especially useful for low-growing crops like lettuce and spinach. Cold frames, on the other hand, are more robust structures that can be used to start seedlings early or extend the growing season. They act like mini-greenhouses, capturing and retaining heat from the sun. You can build a cold frame with materials such as old windows, lumber, or even straw bales and plastic sheeting.
Winterizing Perennials
For perennial plants, preparing for frost and freezing temperatures involves a different set of tasks. Perennials are plants that live for more than two years, and they need special care to survive winter. Mulching is crucial for perennials, as it insulates the roots and helps retain soil moisture. Apply a thick layer of mulch around the base of the plants after the first hard frost. In addition to mulching, cutting back perennials can help them survive the winter. Remove dead or dying foliage, but leave enough of the plant to protect the crown. Some perennials, like roses, benefit from additional protection such as wrapping the base with burlap or using rose cones. For most perennials, leave any cutting back until after temperatures warm up in the spring. Many beneficial insects live in the old parts of the plant over the winter!
Planting Frost-Resistant Varieties
One of the best strategies for dealing with frost is to choose frost-resistant plant varieties whenever possible. Many gardeners have success with varieties bred specifically for cold tolerance. For example, there are frost-resistant tomatoes like the Glacier or Siberian varieties, which can withstand lower temperatures better than standard types. Similarly, frost-tolerant vegetables like Winterbor kale or Windsor broccoli are good choices for regions with unpredictable frost patterns. Investing in these hardy varieties can save time and effort in protecting your garden from unexpected cold snaps.
Conclusion
Freezing temperatures and frost can be damaging or deadly to certain garden plants that are not considered frost hardy. However, learning how to protect plants from frost is simple with these easy instructions and tips. Incorporating these additional measures into your gardening routine can significantly reduce the risk of frost damage to your beloved plants. With a combination of proper timing, effective covering, strategic watering, and selecting frost-hardy varieties, you can enjoy a productive garden even when the temperatures drop. As a fellow gardener, I find great satisfaction in outsmarting the frost and seeing my plants thrive despite the challenges of cold weather. Happy gardening!
References
Frost Hardiness of Plants: http://www.echters.com/FrostHardiness.htm
Frost Hardy – (Gardening): Definition: http://en.mimi.hu/gardening/frost_hardy.html
Frost: How to Protect Your Plants: http://www.gardeningknowhow.com/problems/frost-how-to-protect-your-plants.htm
Frost Protection Methods for Your Plants and Gardens: http://www.thegardenhelper.com/frost.html
Image Credits
Tips for Protecting Outdoor Plants from Frost and Freezing Temperatures: https://www.flickr.com/photos/98176074@N03/15384328913/ (CC BY-NC-SA 2.0) and https://www.flickr.com/photos/lunaspin/2960457357/ (CC BY-NC-SA 2.0)
USDA Plant Hardiness Zone Map: http://www.usna.usda.gov/Hardzone/ushzmap.html
