BLog

As we all know, spring in Minnesota is unpredictable. One day it’s 70 degrees, the next you’re scrambling to cover your plants at 11 PM because a frost warning just popped up on your phone.

If you’ve already planted tender annuals or warm-season vegetables, a late-season frost can undo weeks of work. But with a little preparation, you can protect your plants and keep them thriving until the threat of frost has passed.

Here’s how.

When to Cover

• Cover plants when nighttime temperatures drop below 50°F: While most plants won’t freeze until temperatures hit 32°F, many tropicals and heat-loving plants suffer cold stress in the 40s. This weakens growth and makes them vulnerable to disease.
• Check the forecast regularly from late April through mid-May: Minnesota’s average last frost is around May 11 in the Twin Cities, but frost can happen into late May in some areas.

Which Plants Need Protection

• Tender Annuals: Impatiens, begonias, coleus, petunias, geraniums, mandevilla, hibiscus, jasmine, lantana
• Warm-Season Vegetables: Tomatoes, peppers, cucumbers, squash, beans, basil, eggplant
• What Doesn’t Need Covering: Pansies, snapdragons, kale, lettuce, spinach, and most perennials can handle frost

How to Cover Plants

• Use breathable fabric, not plastic: Plastic traps moisture and can cause more damage than it prevents. Use frost blankets, old bed sheets, burlap, or lightweight blankets.
• Create a tent: This is a Sunnyside tip! Don’t drape fabric directly on plants. The weight can crush blooms, and anything touching the fabric can still freeze.

How to do it:

• Place stakes, tomato cages, or upside-down pots around plants to create a frame
• Drape fabric over the frame so it doesn’t touch foliage
• Anchor edges with rocks, bricks, or soil

This traps warm air around the plant without crushing delicate growth.

• Cover before sunset, remove in the morning: Put covers on in late afternoon if possible to trap the day’s warmth. Remove them once temperatures rise above 50°F and the sun is up — plants need light and air circulation during the day.

Quick Tips

• Try to water plants before temps dip: Moist soil holds heat better than dry soil.
• Move containers to shelter if possible: A garage, shed, or covered porch works great for potted plants and is the easiest way to protect them from the cold.
• Don’t rush to plant: The surest way to avoid frost damage is waiting until after your last frost date to plant tender annuals and vegetables. You can still buy ahead of time – just keep them inside until temps are ready!

What to Do If Plants Get Frosted

If you forget to cover your plants and they experience frost damage, don’t panic. Here’s what to do:

1. Wait before removing damaged growth: Frost-damaged leaves will look wilted, blackened, or mushy. Wait a few days to see how much of the plant is actually damaged before cutting anything back. Sometimes plants recover from what looks like severe damage.
2. Water gently: Once temperatures warm up, water as soon as needed to help damaged plants to help them recover from stress.
3. Prune dead or damaged growth: Once you’re sure which parts of the plant are dead, prune them back to healthy tissue.
4. Be patient: Some plants bounce back from frost damage and continue growing! Others may be too damaged to recover. Give them a week or two to see if new growth emerges.

The Bottom Line

Protecting tender plants from frost takes a little effort, but it’s worth it to save the time, money, and energy you’ve already invested in your garden. A few sheets, some stakes, and 15 minutes of your time can mean the difference between thriving plants and a garden full of frost-damaged leaves. Keep an eye on the forecast, cover when temperatures drop below 50°F, use breathable fabrics, and create a tent to protect blooms. Your plants will thank you!