Weather can be changeable in spring and fall. If temperatures approach 40 degrees Fahrenheit – especially overnight – you want to protect plants from frost or freezing. If you let your crop fare for itself and temperatures get below 28 degrees, your tomato plants are toast.
But your season needn’t be thwarted in the spring nor be over in the fall when there’s an unexpected overnight freeze or frost warning. There are all kinds of ways to protect plants from frost – many of them no cost, low-cost, or DIY solutions. Bookmark this page to have on hand when the forecast projects an overnight frost or freeze.
You water plants regularly, right? Be especially mindful to do so when the forecast looks chilly. A well-watered plant is healthier than a plant that struggles to survive dry soil. But there’s more. Water in the soil acts as insulation. When combined with plant coverings, it can moderate the impact of cool air and keep surface air around the plant warmer, too.
Protect your container tomatoes on your patio, deck, or porch by moving them indoors overnight. Spread newspaper or a tarp on your floor to protect it from soil and moisture.
If you’ve got a covered deck, screened porch, or garage, you can protect plants from frost by moving them into that sheltered spot. And here’s a little-known tip: study where frost falls on your roofline, sidewalks, or plants nearest the house – and which areas escape those effects of cold. Then if you don’t have a covered area where you can place plants on a cold night, you can at least stash them on the most protected side of your home.
If you started plants in a cold frame or greenhouse before you began the process of hardening off, then the natural solution is to return them to their first home for a quick overnight stay when the forecast is iffy. For a long-term fix in the fall, move container tomatoes into your greenhouse for good and keep harvesting fruit for as long as they produce. You can even take tomato cuttings and root them for next season.
Stuff from your cupboards: they’re one of the simplest DIY frost covers for plants. Just pull out extra bed sheets, blankets, towels – even the drop cloth you use to paint indoors – and drape them over plants. Anchor the fabric with bricks or stones. And remove them in the morning when sun peeks out to reheat the soil and warm the plants.
Straw is a popular tomato mulch. If temperatures look cold, then you can get a head start on mulching your tomato plants with straw. heap extra over the tops of young plants over night to protect them. You can remove layers from the plant when the cold night passes but leave straw on the ground at the plants’ bases, thereby completing the mulching task early in the season.
As for leaves: they’re an especially helpful solution for protecting plants in the autumn. Collect the foliage that trees shed and mound it around the base of your tomato plants to protect them. Then, leave the piles there. When it’s time to put the garden to bed for the winter, you can till those leaves into the garden soil.
You may be among the decreasing numbers of consumers who still take a daily or weekly newspaper. Or perhaps you save newsprint sales circulars in your recycling bin. In either case, grab a few clothespins to attach newspapers together to protect plants from frost.
And a special note: cool air sinks and remains closest to the ground, according to meteorologist Jeff Haby at Weather.gov. Surface temperatures are colder than four or five feet above ground. You need only to clip newspapers on the lower several feet of tomato plants to offer adequate protection.
This is an easy fix for early season tomato plants. You can also use buckets, cardboard boxes, or any container that is deep enough to cover seedlings or small plants. Or invert large brown paper grocery bags over plant tops to protect them overnight.
Bell shaped covers, like HotKaps, act like miniature, bell-shaped greenhouses for individual plants. They’re used at the beginning of the season when plants are still small. Affordable and easy to apply, heavy wax-paper or plastic cloche-shaped domes diffuse light around the plant and provide protection from harsh weather.
But you can make your own bell covers, too. Invert a bucket, plastic milk jug, or empty 2-liter soda bottle over each plant. And remember: if you’ve watered the plants, evaporation from the soil warms the overnight air around the plant inside the tiny greenhouse.
Wall-O-Water is a self-standing set of clear tubes that surround a tomato plant. Tubes are filled with water, which warms during the day in the sunlight. Heat radiates at night to keep plants warm. has been effective in temperatures that dip down as low as 16ºF. Red Tomato Teepees operate on the same principle as Wall-O-Water, but their tubes are colored red, allowing water to heat more quickly. Both are reusable in spring and fall and from year to year.
Or you can 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 the water freezes, it will release heat. For greatest effect, paint a few water-holding containers black to maximize daytime heating.
You spend time stringing Christmas lights on and around your house, so why not dust them off and set them in your garden? Use incandescent lights, not LEDs. You need an extension cord to connect the string to an electric source. And you may need to set up ladders, sawhorses, or another elevated pole between which you can stretch the lights. Avoid letting the lights touch foliage to prevent leaf burn. If you cover your set up with sheets or blankets, you can raise temperatures in and around plants up to 7 or 8 degrees.
Air movement can raise temperature in your garden up to seven degrees, which can ward off frost. Use an electric box fan (or two or three, depending on the size of your tomato patch) to circulate air across plants. Elevate the fan a few feet off the ground so warmer air is drawn downward. Keep fan away from water spigots to prevent electrical accidents.
The mulch at the base of a plant protects its roots. But unless the mulch covers the leaves, the plant will be exposed to frost. You can mound mulch, leaves, or straw over your plant to protect it (see #7 above).
Avoid using plastic bags to protect tomato plants from frost. The culprit is not plastic per se, but rather the water that adheres to the surface of plastic bags. When cold or freezing water makes contact with a tomato plant, it damages the leaves, blossoms, and stems.
Along those same lines, gardeners often ask if you can use bubble wrap to protect plants from frost. While the air in bubble wrap acts as a deterrent, why chance the damage perpetrated by the plastic? Tomato Dirt’s recommendation: a thumbs down for bubble wrap.
Yes, if it is not plastic (see above).
Yes. Find a cardboard box with as much depth as possible. Invert it so open end is set on the ground. For larger plants, set stakes or bricks on the ground at four corners around the plant, invert the box, and set it on the four elevated risers.
Frost, yes. A chilly evening, yes. Sustained cold, blowing wind, sleet, snow … no.
When conditions get to be that dire, it’s best to throw in the towel and admit that the fall season is over. It’s time to start dreaming about next year’s crop.
More Ways to Protect Plants from Frost
By Kathy Widenhouse, award-winning writer and owner of Tomato Dirt, a leading online source for growing tomatoes and using them.
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