August 21, 2026 · Updated September 12, 2026
What to cover plants with for frost
Almost anything that traps a still layer of air over the soil works for frost: an old bedsheet, a wool blanket, a cardboard box, an upturned bucket, or a length of frost cloth. They all protect a plant the same way, by holding the ground's heat in overnight. The harder question is whether your yard is cold enough tonight to need one.
How a cover keeps a plant warm
After sunset the soil releases its stored heat upward. On a still, cloudless night, leaves radiate their heat straight up and cool faster than the air around them. Leaves can drop below freezing even while the air near them sits a few degrees warmer. A cover blocks the plant's view of the sky and traps the ground's rising warmth underneath. That trapped warmth is the only protection you get, because the cover adds none of its own.
This is why edges matter. Fabric that reaches the ground on every side keeps the warm air in, while a cover draped over the top like a tent lets that heat spill out the sides. Weigh the hem down with bricks, boards, or soil.
Which material to use
- Frost cloth. Breathes, passes some light, and sheds light rain, so it can stay on through a cold spell without cooking or starving the plant.
- Blankets and quilts. Trap the most heat on a hard night. They block light and hold water, so take them off in the morning.
- Sheets and towels. Fine for a light frost. Keep them from resting on the leaves, since wet fabric on a leaf conducts cold into it.
- Boxes and buckets. Quick cover for a single plant. Set them at dusk and lift them at first light so trapped sun doesn't overheat the plant.
Plastic sheeting is the weakest option. Cold passes straight through it at every point that meets a leaf, and it holds no still air on its own, so it needs a frame to keep it off the plant. For how many degrees each cover buys you, see frost blanket degrees and the right night.
When your yard is cold enough to cover
A cover is worth the effort only when your yard drops to or below a plant's kill point, and your yard is often colder than the forecast. Our own station sits about 7°F under the regional forecast. When the app calls a low of 34°F, our yard lands near 27°F. That gap is the difference between a cover night and a night we can skip. Our first fall frost last year hit on October 3, weeks before the published first-frost date of October 22.
A cover cannot tell you how cold your yard runs, and it cannot rescue a plant already past its kill temperature. So the real work is knowing your low. You can check how much colder your area runs than the forecast with the microclimate checker, and you can decide which beds to cover with when to cover plants.
A free Siltwell account uses a manual offset you enter in Settings, adjusting frost alerts for your site. A connected station on Pro learns the gap between your yard and the forecast after about 14 nights of overlap, then applies it for you.
Tonight, pull the forecast low, subtract the amount your yard runs colder, and compare that number to the kill point of your tender beds. If it lands at or below, cover them at dusk with whatever reaches the ground. If it stays above, save the fabric for a colder night.
Common questions.
- What can I use instead of frost cloth?
- An old bedsheet, a wool blanket, a cardboard box, or an upturned bucket all work, because each one traps the soil's rising heat under a still layer of air. Drape fabric to the ground so the warmth stays in, and weigh the edges down. Keep the material off tender leaves with stakes or hoops where you can, since anything touching a leaf conducts cold straight into it.
- What material is best to cover plants from frost?
- Frost cloth is the easiest, because it breathes, sheds a little rain, and passes some light, so you can leave it on through a cold spell. A blanket or quilt traps more heat than a thin sheet on a hard night. Plastic sheeting is the weakest choice, because cold moves through it at every contact point and it holds no still layer of air.
- Do frost cloths really work?
- Yes, within limits. A cover blocks the plant's view of the cold night sky and holds the ground's warmth underneath, which keeps a covered plant a few degrees above an uncovered one on a calm, cloudless night. It cannot add heat, so it will not save a tender plant on a hard freeze well below its kill point.
- How long can you leave frost cloth on plants?
- Breathable frost cloth can stay on through a run of cold nights, since air and light still reach the plant. Solid covers like blankets, plastic, or buckets should come off in the morning once the air warms, or trapped sun can cook the plant underneath. Uncover on the first mild day so the plant gets full light again.
- How do I know if tonight is really a cover night?
- Compare tonight's low to the temperature your own yard reaches, not the regional forecast. Cold air is denser, so it drains into low spots and settles on still nights, and many yards run several degrees colder than the published number. Cover the tender beds when your real low lands at or below their kill point.
Related guides
Frost cloth and when to cover plants
Learn how frost cloth traps a few degrees, which fabric to use, and how to pick the nights your yard actually freezes.
Can plants recover from cold shock after a frost night
How cold shock kills plant tissue, how to tell what survived, and when to prune, water, and feed a cold-damaged plant.
Will frost kill potato plants in your yard
Frost blackens potato leaves near freezing, but tubers usually regrow. Learn when to hill or cover, and how to tell if your yard got that cold.
Free planting tools
- When to plant shows the last date to sow each crop before your fall frost.
- Microclimate checker shows how much colder or warmer gardens near you ran than the forecast low.
- GDD estimator adds up a typical season's heat and shows which crops can ripen where you are.
