Frost Tonight? What to Cover
Frost tonight? Pick your city and this tool pulls the coming night's forecast low, flags the clear, calm nights when frost forms even above zero, and tells you exactly which crops to cover tonight.
Will it frost tonight? Select your city below and the tool reads Open-Meteo's hourly forecast, takes the low for the coming night, and compares it against each crop group's frost tolerance. The key gardening point: on a clear, windless night a leaf can cool 2–4°C below the 2 m air low the forecast reports, so a forecast low of 3–4°C can still bring ground frost. Tender crops (tomatoes, peppers, basil, squash) should be covered at 3°C or below; hardy crops (kale, spinach, carrots) shrug off frost and even sweeten.
We remember your pick. Frost is very local — for your exact yard, use the location button.
The simplest way to save tender crops on a frost night: a breathable row-cover blanket lets light and water through, buys the few degrees that matter, and can stay on for several days during a cold snap.
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How to protect plants from frost tonight
1. Cover before nightfall
Drape row cover, an old sheet, a blanket, or a cardboard box over tender plants before sunset, while there's still ground warmth to trap. The cover should reach the soil so it holds the earth's heat in — not just sit on the foliage.
2. Water the soil in the afternoon
Moist soil holds far more heat than dry soil and releases it overnight. A good afternoon watering before a frosty night can buy the plants 1–2°C at ground level.
3. Take covers off in the morning
Pull sheets and plastic once the sun is up and the frost has lifted, or heat builds underneath. Breathable row-cover fabric can stay on for several days.
4. Worst case: clear, calm, dry nights
Cloud acts like a blanket and wind mixes warmer air down — both reduce frost. The nights to watch are clear and windless: that's when ground frost runs colder than the forecast low.
How to tell if it will frost tonight
The tool pulls Open-Meteo's hourly temperature forecast for your city and takes the low for the coming night — not the already-passed daytime low. It also checks cloud cover and wind: on a clear, windless night the ground and leaves lose heat to the open sky by radiation and can drop 2–4°C below the reported air temperature. That's why a forecast low of 3–4°C is already a frost risk for tender crops.
Each crop group has a different threshold: tender crops (tomatoes, basil, squash) are damaged the moment temperatures near 0°C, half-hardy crops (lettuce, chard) take a light frost, and hardy crops (kale, spinach, carrots) shrug off a real frost and actually sweeten. Because forecasts change, check back each evening through frost season. For the historical averages, see the first frost dates.
Frequently asked questions
At what temperature should I cover my plants?
Cover tender crops (tomatoes, peppers, basil, cucumbers, squash, beans) once the forecast low reaches 3°C or below, because on a clear night frost forms at ground level above zero. Half-hardy crops (lettuce, chard, celery) take a light frost to about -2°C. Hardy crops (kale, spinach, carrots, cabbage) handle -5 to -6°C and sweeten in frost — no need to cover them unless a hard freeze is coming.
Can frost form above freezing?
Yes. Forecasts report the air temperature at 2 m above ground. On a clear, windless night, leaves lose heat to the sky by radiation and can drop 2–4°C below that value — so a reported low of 3–4°C can still bring frost at plant level. That's why this tool recommends covering tender crops at 3°C on a clear night.
How do I protect plants without row cover?
Anything that traps ground heat works: old sheets, blankets, towels, cardboard boxes, or buckets turned over each plant. The cover should reach the ground to hold the soil's warmth. Avoid plastic touching the foliage directly — the leaf freezes wherever it contacts. Remove everything in the morning.
Does frost damage all vegetables?
No — many improve. Kale, spinach, carrots, parsnips, and Brussels sprouts convert starch to sugar in the cold and taste sweeter after the first frosts. It's the warm-season crops — tomatoes, peppers, basil, squash, beans — that frost kills, and those are the ones to cover or harvest ahead of time.
How often should I check?
In frost season (spring and fall), check each evening — the forecast changes day to day and a single frost can end your tomatoes. Bookmark this page; it always shows the coming night. For an automatic email heads-up, sign up for your city's frost alerts.