The First Frost Is Coming. Here's How to Save Your Plants the Night It Hits

You check the forecast before bed and see it: a low of 31°F. Your tomatoes are still ripening, the mums on the porch look perfect, and the basil is going strong. Then you wake up to blackened, droopy leaves. Most of that damage is preventable with a little work the evening before.

Here is what frost actually does, which plants are in danger, and a simple plan for the night it arrives.

Frost, Light Freeze, Hard Freeze: What the Numbers Mean

Not every cold night is equally dangerous. Gardening references such as The Old Farmer's Almanac use a few rough thresholds:

• Around 32°F (0°C): a light frost. This is enough to kill tender plants like tomatoes, peppers, basil and most annual flowers.

• 28°F to 32°F: frost-tolerant crops such as broccoli, carrots and beets usually come through fine.

• 28°F and below: a hard freeze. Even hardy greens like spinach and kale start to suffer.

One surprise: frost can form on plants even when the official air temperature is as high as 38°F. Thermometers are usually mounted several feet above the ground, while cold air settles low, right where your plants are.

Know Which Nights Are Risky

The first frost of the season usually arrives on a clear, calm night. Without clouds acting as a blanket, heat stored in the ground escapes quickly into the sky. A dry, cloudless, low-humidity afternoon is often a warning sign of a cold night ahead.

Your area's typical first frost date is only an average. In Georgia, for example, University of Georgia Extension notes that the first frost usually arrives in mid-November but can come earlier. Watch the local forecast rather than the calendar.

Which Plants Need Help First

Warm-season vegetables are the most vulnerable. Utah State University Extension says peppers, tomatoes, cucumbers, melons and squash can be damaged at 33°F. Beans belong on that list too.

Cool-season crops are much tougher. Peas, lettuce, spinach, beets, carrots, onions, broccoli, cauliflower and cabbage are considered cold hardy and can often handle a light freeze with little damage. If you are short on time or covers, protect the warm-season plants first.

The 6-Step Plan for Frost Night

1. Water during the day. Moist soil holds more heat than dry soil and releases it overnight. UGA Extension suggests watering about two days ahead or the day before the frost. Water early so leaves are dry by night, and do not flood the bed.

2. Move containers. Bring tender potted plants and houseplants indoors, or group pots against a south-facing wall where they can soak up stored warmth.

3. Cover before sunset. Use frost cloth, old bedsheets, blankets or even upside-down buckets and baskets. Covering in the early evening traps heat that the soil absorbed during the day.

4. Let the cover reach the ground. A cover works like a tent, holding in warmth that rises from the soil. Weigh the edges down with bricks or stones so wind cannot lift them, and check for gaps.

5. Be careful with plastic. If plastic sheeting touches the leaves, those leaves can freeze. And if you leave plastic on after sunrise, it can trap too much heat and scorch the plant. A fabric layer underneath helps if plastic is all you have.

6. Uncover in the morning. Once temperatures rise above freezing, remove the covers so plants get sunlight and do not overheat.

How much difference does this make? According to Utah State University Extension, covers generally keep plants 3 to 5 degrees warmer than the surrounding air and are useful on nights down to about 28°F. Below that, harvest whatever you can.

Cheap Tricks That Actually Help

• Thrift-store blankets: old comforters make inexpensive, reusable frost covers.

• Fallen leaves and straw: pile them around low-growing plants and the bases of perennials as insulating mulch, then pull them back when the weather warms.

• Harvest early: green tomatoes picked before a hard freeze can often ripen indoors at room temperature.

If Frost Gets There First

Do not rush to prune right away. Damage can take a day or two to show fully. Once you can clearly see which parts are dead and mushy, trim them off. For annual vegetables like tomatoes and squash, a hard freeze usually means the season is over, so it is time to clean up the bed and plan for spring.

The Bottom Line

Frost protection is not complicated. Watch for a clear, calm night with a low near 32°F, water during the day, cover your tender plants before sunset, and uncover them in the morning. A few old sheets can buy your garden several more weeks of harvest.

What are you trying to save from the first frost this year: tomatoes, flowers, or herbs? Share your best frost trick in the comments.

This story was written with the help of AI tools. Sources: Utah State University Extension ("Five Ways to Protect Plants from Dipping Temperatures"), University of Georgia Cooperative Extension (early frost guidance for late-season flowers and vegetables), and The Old Farmer's Almanac (frost temperature thresholds and protection tips).