11 Late-Spring Frost Strategies

Learn what to do when a late spring frost threatens veggies and flowers you just bought—and maybe even planted.

By: Julie Martens Forney

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Photo By: Julie A. Martens

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Photo By: Gardener's Supply Co. at Gardeners.com

Photo By: Julie A. Martens

Photo By: Gardener's Supply Co. at Gardeners.com

Warm-Season Annuals In Container Garden

In early spring, it’s easy to plant too early, especially when you’re fighting spring fever. A few warm days can coax even the most experienced gardener to throw caution to the wind and tuck warm-season annuals, like coleus, begonia and petunia, into containers. Or maybe you decide to get a jump on your tomatoes and slip seedlings into the garden sooner than you should. A sudden cold snap can endanger these early season efforts—but you can protect plants with these easy strategies.

Shift Pots to a Protected Spot

The easiest way to protect plants when frost threatens is to move them to a sheltered location, such as on a porch, beneath an elevated deck or inside a garage or shed. On a porch, cluster pots together against a wall. Huddling containers in a small group makes it easier to cover them with a frost blanket or tablecloth, if temperatures require. The small cluster also raises humidity around plants—which helps elevate temperatures near leaves since moist air takes longer to cool.

Make Plants Mobile

Gather plants that you haven’t tucked into soil or containers in a wagon or wheelbarrow, and stash them in a garage or garden shed overnight. Just be sure to wait until temperatures rise before moving plants outside the next morning to soak up some sunshine. Use caution with this method if you’ll open the overhead garage door for an early morning exit. Temperatures may still be freezing at this point, and opening the door will allow a rush of frigid air to envelope plants.

Lower Hanging Baskets

Lower hanging baskets from their hooks and set them on the ground in a protected location. If baskets are too full to sit directly on the ground without breaking stems, place them on an inverted bucket or pot. The reason you want to move baskets is that air near the ground will stay warmer longer than air at hanging level.

Water Plants

Water plants just before the sun sets. As water evaporates from soil overnight, it will warm the air around plants. Use caution when watering containers if overnight lows are dipping below 32 degrees Fahrenheit. Soil in a large pot shouldn’t freeze solid at that temperature, but smaller soil volumes, like in 4-inch pots or cell packs, might. For these small containers, toss a beach towel or old sheet over plants for extra protection.

Linen Closet Plant Covers

Keep a supply of plant covers on hand fresh from the linen closet. Towels, tablecloths, sheets, blankets—any type of fabric works well to keep frost from forming on plants. Pillowcases make effective vertical covers for individual plants or pots. Get covers into place before dusk. As soon as the sun sets, soil starts releasing heat, and you want your cover to trap that heat around plants. Remove covers in the morning, after frost melts.

Floating Row Cover

Frost blankets, a type of floating row cover, are made from synthetic or plastic fibers and come in different thicknesses. Thicker blankets provide greater frost protection. Use frost blankets like sheets or towels. Place them over plants before dusk, and remove in the morning when the sun has melted frost. Because frost blankets allow light to pass, you can leave them in place during an extended cold snap. Anchor edges to keep cold air out.

Pot Cover for Frost Protection

Individual frost blankets for pots and hanging baskets feature a drawstring that allows you to pull the bag closed around a plant. These covers come in different weights of blanket material, so make sure you get the one that provides the amount of frost protection you need. Look for covers in different sizes. It’s a good idea to just go ahead and purchase the largest size to provide the most versatility.

Homemade Hot Cap

Hot caps are individual plant covers that you slip over seedlings to protect them from the vagaries of early spring weather. You can purchase plastic hot caps with built-in, manually operated vents for releasing heat. Make your own hot caps using plastic gallon jugs. Simply cut off the bottom. Place lids on jugs before cold nights, and remove them during warm days. Cut a slit in the handle and slip a stake through and into soil to ensure jugs don’t blow away on blustery days.

Wall O’Water Tepee

Wall o’water tepees are a plastic sleeve of empty tubes made to surround garden plants. You fill the tubes with water that absorbs sunlight during the day, creating a mini-greenhouse effect around plants. When temperatures tumble to freezing at night, the water slowly freezes, releasing radiant heat that keeps air around plants toasty. Red tepees offer a new twist on this tried-and-true garden idea, bathing seedling tomatoes with the ideal light wavelength to maximize growth.

Portable Cold Frame

A portable cold frame offers a frost blanket attached to a sturdy frame. Some cold frame models, like this one, have sides that roll up or down to allow air movement and heat release during the day. Before dusk, close up the sides, and you have a miniature greenhouse to keep plants warm and cozy during a late-spring frost.