Don’t Let Your Blooms go “BRRR!”
10/11/2024
Battling the winter frost is a frustrating but unavoidable rite of passage for Minnesota gardeners. The last thing we want as northern gardeners is to see our hard work lost as plants succumb to a sudden freeze. We can bring potted plants indoors when temperatures drop, but many of our foliage-bearing friends are already stuck in the ground. What strategies can we employ to ensure our most sensitive outdoor plants survive the frost this year? Let’s break the ice on this topic!
Plant Selection is Key!
Choosing plants that are well adapted to the plant hardiness zone of your area is one of the first and most important steps to ensuring your plants survive the chill. Visit the USDA Plant Hardiness Zone Map to determine the Plant Hardiness Zone range where you live, then choose plants accordingly.
Overall, the state of Minnesota falls within Plant Hardiness Zones 2-5, with the Twin Cities metro falling in Zones 4-5. It’s certainly possible to cultivate plants that fall outside of this range, but it will take extra care, and success will be less guaranteed. The Minnesota Department of Agriculture offers a great place to start finding plant options with their 2024 Cold Hardiness List. You can also visit the Minnesota DNR’s Native Plant Suppliers page to find quality sources for the plants you’re seeking.
Figuring Out Frost Dates
Read up on the care needs for your chosen plants—even if a plant falls within your hardiness zone, it may be especially sensitive to unexpected cold snaps. Early frost in the fall and late frost in the spring are especially dangerous for certain plants, as they interrupt the active/dormant cycles that plants run through as the seasons change. If your plants freeze in the fall before they can go fully dormant, they may be damaged, and the same is true if they bloom early in the spring and are then hit with a wave of frost.
New growth and opening buds are the most vulnerable to frost damage. For this reason, it pays to be a little patient in the spring and wait until the threat of frost is quite low before planting especially sensitive plants. For detailed information on the final spring/first fall freeze probabilities for your area, check out the Minnesota DNR’s Frost Date Probabilities page. Remember that the statistics listed are averages—keep an eye on your favorite weather app, and watch for frost warnings in the late fall and early spring.
Protecting Sensitive Plants
So, once your plants are in the ground, and you’re on frost-watch, how can you protect your fragile friends from untimely cold spells?
The first line of defense is plain-old good garden care—ensure that your plants are healthy, free of pests and properly watered, and that any fragile stems or trunks are properly supported by trellises as needed. Wherever possible, planting in sunny locations that are sheltered from the wind can also help, as the temperature will drop the fastest in shady and windy spots when the weather changes.
Avoid pruning your plants when frost dates are near, as this creates a lot of added strain. Mulching around the base of plants is another simple way to help vulnerable roots trap a little heat. Piling dead leaves around plant bases can be a great way to do this in the fall. And believe it or not, snow actually helps to hydrate and insulate plants—if there’s already snow on the ground, don’t clear it away from your plants.
Frost Protection Cloths and Cloches
Frost protection cloths can also be used overnight to help plants hold on to some of their heat during unexpected chills. There are frost blankets and row covers specifically for this purpose, but many gardeners make use of old fitted bedsheets or thin blankets with success as well. Remove cloths in the morning so the plants can gain the full benefit of the sun. Be sure not to use plastic tarps, as this will actually trap moisture and even conduct cold into the plants and make their environment even less optimal.
Cloths should be placed loosely over the plant and anchored to the ground with gardening staples or bricks. Make sure not to tie cloths tightly around the bases of your plants, as the goal is partly for the cloth to trap some of the radiant heat coming up from the ground. For smaller delicate seedlings, gardening cloches (glass or plastic domes) can provide shelter. Gallon milk jugs can even be cut to make homemade cloches—just make sure your cloche is big enough that your plant isn’t pressed tight against the plastic or you’ll again have the cold conducting problem mentioned above.
Minnesota can be a tricky place to cultivate a garden, but with vigilance and careful preparation a sudden frost doesn’t have to spell doom for your plants. Proper plant selection, garden tending and the use of insulation are all ways that you can help your plants to survive unexpected cold snaps. As you grow in experience, you’ll learn which of your plants need which interventions when the temperature dips and the frost starts to bite. Visit the University of Minnesota Extension’s Yard and Garden page for more articles on garden care, and consider taking a free online course like “Fall Into Winter” through the Ramsey County Master Gardener program.
References and Further Reading
Minnesota Department of Agriculture—2024 Cold Hardiness List
Minnesota Department of Natural Resources—Native Plant Suppliers
Minnesota Department of Natural Resources—Final Spring/First Fall Freeze & Frost Date Probabilities
University of Arizona Cooperative Extension—Backyard Gardener—Frost Protection
University of Minnesota Extension—Winter protection for plants
University of North Carolina Cooperative Extension—How Do I Protect My Garden From Frost?
U.S. Department of Agriculture—USDA Plant Hardiness Zone Map
Scott Lore
Master Gardener Volunteer
University of Minnesota Extension
Scott is a member of the University of Minnesota’s Extension Master Gardener program. He lives in St. Paul with his wife Sam and their two cats, Yoshi and Toph. Scott is passionate about nature, photography, writing, music, and tabletop games. His enthusiasm for gardening stems from a long-term goal of being able to sustainably grow his own food, cultivate native species, and support pollinators to help our environment thrive.
Photo Credit
Asta Co via Unsplash—https://unsplash.com/photos/a-close-up-of-a-plant-with-frost-on-it-snRoQEqHev8