September 21, 2026

How to protect plants in winter without covering every night

The nights that matter are the ones your yard's low drops below a crop's kill temperature, and those are fewer than a winter of forecasts suggests. To protect plants well, insulate the roots, cover the tender crops on the right nights, and know your yard's real low. This guide walks the steps and names where each one can mislead you.

Why some winter nights matter and others don't

Once the sun sets, warmth stored in the ground radiates upward toward the open sky. On a still night the leaves shed that warmth faster than the surrounding air loses its own. Because dense cold air sinks, it slides down slopes and settles in the lowest beds. A cover traps some of that radiated heat and holds the leaf a few degrees above the open air. A hard frost only threatens a plant when your yard's low crosses that plant's kill temperature, so most winter nights ask nothing of you.

Step 1: Find each crop's kill temperature

Write down the low each crop can survive. Tomatoes and peppers take damage close to 32°F, while spinach, kale, and garlic hold through hard frost. Sort your beds by that number so you know which ones need watching. Our hardy greens and garlic sit outside all winter without a cover.

Step 2: Learn your yard's real low

The forecast reports a regional low, and your yard can run colder. In our own garden the station reads about 7°F below the forecast, so our learned offset is -7°F. That gap moves our first fall frost from the published 10-22 to an effective 09-30, three weeks earlier. A connected station learns this offset for you; a free account lets you enter a manual offset in Settings instead. You can check how much colder your area runs before you connect anything with the microclimate checker, and see the setup at connect your station.

Step 3: Mulch the roots now

Spread a few inches of straw or leaf mulch over the root zone. Mulch slows the soil's heat loss, so the ground stays warmer and swings less between day and night. This protects roots and crowns even when the leaves above take frost. Do this once and it works every night without you.

Step 4: Cover only on the nights that cross a threshold

Drape frost cloth over hoops so it clears the foliage, and pin the edges to the ground to trap soil heat. Cover the beds whose crop threshold your yard's low will cross that night. Skip the beds whose crops are hardy. For the mechanics of degrees and timing, see frost blankets and the right night.

Step 5: Vent covers by mid-morning

Pull the cover back once the air rises above freezing. Cloth left on all day traps damp air and blocks light, which invites rot on greens. Re-cover in the late afternoon if the next night crosses a threshold again.

What can go wrong

A learned offset is an average bias across many nights. It cannot tell you that one still, clear night will pool colder in a low bed than the forecast plus your offset suggests. Leave a margin on your tender crops. Wind and cloud change how fast the ground loses heat, and a cover pinned loose lets that trapped warmth escape. Our coldest night this year hit 3°F, well below anything a single cloth layer buys back, so some nights the answer is to accept the loss on plants that cannot take it.

Start by tagging each bed with its crop threshold tonight, then set your offset so the frost alert reflects your yard rather than the forecast. For the reasoning behind reading your real lows across a season, see winter protection and your real lows.