August 11, 2026 · Updated September 12, 2026

What a frost blanket for plants buys you

A frost blanket buys your plants a few degrees, and it does that by trapping the heat the ground releases to the sky after dark. You get those degrees only if the cloth is down before that heat escapes, on a night when your own yard falls below the plant's limit. Get the timing right and the fabric works. Get it wrong and the plant reaches air temperature no matter how good the cloth is.

How the blanket holds heat

After sunset the soil radiates its stored heat upward, and a clear sky gives that heat nowhere to bounce back from. When the air is calm and cloudless, a plant sheds heat that way faster than the surrounding air cools. Its leaves can drop below air temperature and freeze while the thermometer reads a few degrees above freezing. A frost blanket sits between the plant and the sky and intercepts that radiant loss. It re-radiates some heat back down and traps a pocket of ground-warmed air around the plant.

What decides how many degrees you get

• Fabric weight. Heavier fabric traps more heat and buys more degrees.
• Reaching the ground. The blanket has to drape to the soil so it holds the heat rising from the ground, not just cover the top of the plant.
• Covering early. Put it on while the ground still holds its heat, before sunset, so there is warmth to trap.
• The sky. Calm, cloudless nights drive the fastest radiant loss. Wind or cloud cuts that loss, so the blanket matters most when the air is still and the sky is clear.

A blanket slows the escape of heat the ground already holds. On a long, deeply cold night that reservoir empties and the plant settles at air temperature anyway, which is why cloth alone will not carry tender plants through a hard freeze.

Can the blanket touch the plant

It can rest on sturdy leaves, but the contact points lose the most heat. Where the fabric presses on a leaf it conducts cold straight through, and that spot can freeze while the covered air keeps the rest alive. A hoop or a few stakes that hold the cloth off the foliage protects tender growth. Our guide on when to cover plants walks through the timing.

Frost cloth or a frost blanket

Both do the same job at different weights. Frost cloth is a light spun fabric that breathes and passes light, so it can stay draped for several cloudy days. A frost blanket is heavier, so it traps more heat and buys more degrees, but it blocks light and you remove it each morning. Match the weight to the plant in our frost cloth material guide.

The night your yard needs it

The blanket matters only when your yard dips below the plant's line, and the published frost date rarely names that night. Dense cold air drains downhill on calm nights and pools in low beds. Those low beds can freeze while a raised bed a few feet away stays clear. Our own beds run about 7\u00b0F colder than the forecast. The first fall frost we recorded hit on October 3, nearly three weeks ahead of the published date. You can compare your yard to the area with the microclimate checker.

Siltwell learns your offset from the overlap between a connected station and the forecast, and it trusts that learned number after about 14 nights of readings. Once the offset holds, each frost warning is adjusted to your station, so you cover the beds on the night your yard falls below the line rather than the night the region does. Until then you can enter the offset by hand. See how to connect a station to learn it automatically.

Before the first cold snap, set a hoop or frame over the tender beds so the cloth never rests on the leaves, then check your yard's real low against the forecast so you cover on the right night.