How to Protect Your Flowers From Frost So They Can Survive a Cold Snap

As the seasons shift from fall to winter, the weather can become somewhat erratic. It’s common to have below-freezing temperatures one week, followed by a stretch of warmer weather in the next. With that in mind, now is the time to plan how you'll manage your garden’s first cold snap.

Even a light frost can severely damage or even destroy an entire flower bed. However, with proper barriers in place, you’ll be able to extend the life of your blooms and enjoy their beauty well into autumn. Here, our experts share helpful tips to keep your beloved flowers safe from any frigid dangers.

Frost vs. Hard Freeze

First, it’s a good idea to understand the difference between a frost, freeze, and hard freeze. Lynne Holland, a horticulture professional and gardener at the University of Maine Cooperative Extension, shares that frost is when the temperature drops between 31 to 33 degrees Fahrenheit. “Below 31 degrees is considered a freeze," she says. "Anything under 26 degrees is a hard freeze.” Keeping an eye on your USDA Hardiness Zone Map will help you stay prepared for falling temperatures.

Flowers That Need Protection

Cold temperature affects the cell walls of plants, causing the water inside to expand and contract.  While the plant may look fine in the morning with just a touch of white frost, the cell wall will collapse once it warms back up, Holland warns, causing the leaves to quickly decay. “Delicate buds and petals can brown or blacken for the same reason," she says. Plants like cosmos, begonias, geranium, salvia, dahlias, zinnia, and basil call for protection when frost is on the forecast.

On a warmer note, “Dianthus, sweet pea, miniature rose, calendula, stock, snapdragon, and rosemary can take a light frost," says Holland. "Pansy, violet, ornamental cabbage, sedum, and sage laugh at a light frost."

Cover the Plants

The best way to prevent frost damage in your flower garden is to create a blanket or barrier between the descending cold and the blooms you want to save. “To cover your plants, you can use old bed linens, towels, or frost blankets,” shares Emily Scott, owner of Scott Farm in Maine. Agribon, an insulated row cover, is another great option for plant protection. Not only does it protect against frost, but it also traps heat from the soil, creating a greenhouse environment.

“Make sure the entire plant is covered loosely, and secure the edges so the material doesn’t blow in the wind,” says Scott. To secure the cover, she recommends using stakes, rocks, and any other heavy objects that are readily available. 

Move Garden Containers Indoors

If possible, move your potted flowers inside where they'll be safe from frost. You can also relocate them into a garage or shed. However, when temperatures are near freezing, they need to be sent to a more insulated indoor location.

Add Mulch

Mulch is a great way to insulate your flowers from the dangers of frost. Scott recommends applying two to three inches for optimal protection. This will allow the warmth to remain in the soil.

Use a Cloche

"A garden cloche—a rounded cover that acts as a greenhouse around a single plant—is an easy and effective way to prevent frost,” Scott says. “You don’t need to mat down any edges, but you do want to make sure the lid is anchored down.” Be sure to remove the cloche the next day to prevent the plant from overheating. You can find cloches at your local garden center or online. Alternatively, you can DIY a cloche by cutting off the bottom of a gallon-sized milk jug and placing it over the plant.

Water Well

While you may think that watering plants before a frost will cause them to freeze, it’s actually quite the opposite. Moist ground stays warmer than dry ground. “Watering the plant the day of the frost will allow the water to hold the heat in the soil and radiate it back up,” says Holland. After watering, adding a blanket or cloche will give your plants added protection.