How to Protect Plants from Frost, According to Pros
The start of fall brings so many familiar comforts of the season. Whether you’re excited to consume pumpkin-flavored everything, pull on your coziest sweaters, or traipse through the local corn maze, summer’s heat giving way to cooler temperatures is a respite. However, while you’re enjoying all the season’s festivities, those chilly temperatures could be harming something: your outdoor plants. (Fall isn’t the only time frost is a concern, though, as the early wavering temperatures of spring can also bring climate uncertainty.)
Depending on where you live, frost dates vary, so if you want to protect your outdoor plants then consulting an almanac is essential. As a general guide, leafy plants will die during a light freeze (29°F to 32°F), while a severe freeze below 24°F will heavily damage most garden plants. After investing time and sweat equity into creating a beautiful outdoor space, the last thing you want is frigid temperatures slowly killing off your efforts. For happy outdoor vegetation, I had two garden and plant experts weigh in with seven tips to protect your plants from frost.
Identify vulnerable plants.
One of the first steps in defending beloved flora is realizing how well they can tolerate frosty conditions. Brock Ingham, owner of Bigger Garden, says that knowing which species are most susceptible to frost damage is crucial. “It helps you prioritize which plants require the most attention and care during cold-weather events,” he says. Knowledge is half the battle, so you know where to start if you’re short on time and temperatures drop.
Prioritize protection for non-native plants.
Generally, flora not native to your region won’t be acclimated to your climate or equipped to handle harsh temperatures and quick fluctuations. The best way to determine if a plant is native is to check with a hardiness zone map. If you live in Zone 5 and have a Zone 9 non-native plant outdoors, it probably won’t survive unless you cover it. Ingham recommends covering out-of-area plants with a frost cloth or blanket and bringing potted specimens indoors. Susceptible plants outside during frost can show signs of distress, such as wilting, dieback, or leaf browning.
Cover tender plants.
Plants classified as tender, regardless of their native status, should also take priority when the first frost arrives. “Protecting can involve covering them, moving them to a more sheltered location, or bringing potted specimens indoors,” says Ingham. Annuals, tropical plants, and some perennials fall into the tender category, as do many herbs and vegetables. “Peppers, tomatoes, eggplants, and other subtropical species need protection, whereas cool-season vegetables like kale, spinach, and broccoli may be fine,” adds Justin Hancock, a horticulturist with Costa Farms.
Leave hardy landscape plants alone.
Hardy trees, shrubs, and perennials typically fare well through the winter, so they’ll survive frost. “These naturally build up more resistance to cold temperatures as the weather cools, so unless there’s a sudden and intense onset of cold weather, you don’t usually need to protect these plants,” advises Hancock. Established vegetation can withstand frigid temperatures and start flourishing once the weather warms, barring that they are healthy and disease-free.
Let annual plants perish if you’re ready.
The name annual indicates one year, and these plants tend to get lanky when they grow over long periods. Because they thrive best for one season, you can ease your mind by letting them die off. Often, they’ll reseed so that you may find marigolds in the exact location next year, which is a perk.
“Annual plants complete their life cycle within a single growing season,” says Ingham. They don’t have the opportunity to become cold-hardy over multiple years, making them especially prone to frost damage. If you’re not ready for these plants to die off, protection is critical — but know that it’s totally OK if you just let them go at the end of the season.
Use the correct type of protection.
Oscillating temperatures can leave you scurrying to cover and uncover weaker plants. “If the weather forecasts a light frost one night and the rest of the forecast looks otherwise fine for the next several days, you can get away with a sheet, towel, or frost cloth before the sun goes down,” recommends Hancock.
He also notes to avoid laying plastic sheets directly on foliage, as they could damage tender vegetation. Surprisingly, Hancock suggests a summer-centric idea for staving off freezing temperatures. “For light frosts, running a sprinkler can also prevent frost damage,” he advises. As long as water flows, it isn’t frozen, keeping warmer degrees flowing over susceptible plants. (This will not, unfortunately, be workable in extreme cold temperatures.)
Ingham also uses this approach, citing that wet soil holds heat better than dry. “Native plants like coneflowers or hardy perennials like sedum can benefit from this approach,” he adds. In addition to blankets and frost cloths, Ingham also says that foam covers and mulch work, depending on the application.
Foam covers fit over individual plants and are ideal for more vulnerable specimens and non-native species. They fend off frost by forming a protective covering around plants. A thick layer of mulch benefits perennials and shrubs, like hydrangeas and roses. “It acts as a natural insulator, safeguarding the soil and roots while maintaining a stable temperature,” says Ingham.
Monitor the weather forecast.
Of course, one of the best steps in staving off frost is to keep track of impending low temperatures. Install a weather app on your phone or consult the web for the highs and lows in your area. “Monitoring weather forecasts and the condition of your plants is essential for making timely adjustments to your protection strategy and ensuring their well-being,” advises Ingham. Ultimately, tailor your protection method to your plant’s specific needs and the frost’s severity.