July 27, 2026 · Updated September 12, 2026

Frost cloth and when to cover plants

Frost cloth works, and it earns you a few degrees on the nights it matters. It holds the heat the ground gives back after dark, so it rescues a plant that would otherwise land just below freezing. The hard part is knowing which nights your yard drops below freezing, because your yard can run colder than the forecast.

How frost cloth holds a few degrees

After sunset the soil releases the heat it stored during the day and radiates it skyward. When the night stays still and cloudless, a leaf loses its own heat upward faster than the surrounding air cools. That is why frost forms on foliage while the air thermometer still reads a few degrees above freezing.

Frost cloth puts a barrier between the plant and the sky. It slows that radiant loss and traps a thin layer of ground-warmed air around the leaves. The cloth holds the ground's heat a little longer. A little longer is often all a tender plant needs to survive the coldest hour before dawn.

Which fabric traps the most

Weight and weave decide how much a cover holds. A dense, spun fabric slows more heat loss than a thin sheet, and a cover draped straight onto the leaves loses ground where cold metal or wet cloth touches them. Hoops or stakes keep the fabric off the foliage and hold the warm air pocket.

• Spun row cover. Breathable polypropylene holds the most heat and lets light and rain through, so it can stay on for several cold days.
• Sheet or blanket. Fine for one night over a frame, but pull it off in the morning before the sun bakes the plant.
• Plastic. Traps the least and burns leaves at every contact point, so use it only over hoops and never on bare foliage.

For a fuller walk through materials and how long each one can stay put, see our guide on frost cloth material and duration and what to cover plants with for frost.

The temperature that tells you to cover

Cover tender plants when the adjusted overnight low for your yard reaches or drops a little below 32°F. Peppers, tomatoes, squash, and cucumber take damage right around freezing, so a forecast of 34°F to 36°F is already a warning on a clear, calm night. Watch the low your yard will hit. The regional forecast runs warmer than a cold pocket in your beds.

Here the cloth reaches its limit. A few trapped degrees rescue a plant on a night that grazes freezing, and they do nothing against a hard freeze many degrees below the plant's kill point. On those nights the plant needs to come indoors or come out of the ground.

Is your yard colder than the forecast

Cold air is denser than warm air, so it drains downhill on still nights and pools in low spots, dips, and pockets against fences and walls. A yard in one of those pockets freezes while the forecast, tuned to a wider area, still reads a few degrees above. That gap is why a plant covered on the forecast schedule can still take damage.

In our own garden the station runs an average of 7°F below the forecast. That pulls our first fall frost from a published 10-22 to an effective 09-30. Last year the first fall frost we recorded landed on 10-03. Cover nights in our yard start more than a week before the regional date would suggest.

You can size your own gap without hardware. The microclimate checker lines up the forecast low with what nearby home stations have logged over the past few nights. It reports the typical gap for your area, warmer or colder. It gives an area indicator. Your exact yard can still differ from that.

Tonight, find the adjusted low for your own yard, then decide. If it reaches 32°F or below, get a breathable cover over your tender beds on hoops before sunset, while the ground still holds its heat. To have your station measure that offset for you, set one up in your beds.