Tomatoes are frost-tender, so a cold night can end the season fast. A light frost damages leaves and exposed fruit, and a hard freeze kills the plant. Enter tonight’s forecast low to see whether your tomatoes are safe, need covering, or should be picked now.
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What Your Result Means: the action is for established plants outdoors. On clear, calm nights, ground-level frost can form even when the forecast reads a few degrees above freezing, so protect early if the low is near 36°F. When a hard freeze is coming, harvest what you can.
Will Frost Kill My Tomatoes?
It depends on how cold it gets. A touch of frost harms leaves and exposed fruit, while a hard freeze kills the whole plant. Enter tonight’s forecast low and the tool tells you whether to relax, cover the plants, or harvest.
- Enter the Forecast Low, the coldest temperature expected overnight.
- Read the Action, safe, cover, or harvest, based on how cold it will get.
- Protect or Pick, before nightfall, since cold settles after dark.
What Each Result Means
| Result | What It Tells You |
|---|---|
| Risk verdict | How dangerous tonight is for tomatoes |
| Action | Whether to cover, harvest, or do nothing |
| Tip | How to protect or what to pick |
Action by Temperature
What to do at different overnight lows for tomatoes growing outdoors.
| Forecast Low | Risk | Action |
|---|---|---|
| Above 45°F | None | No action needed |
| 40 to 45°F | Cold, no frost | Cover tender young transplants |
| 33 to 39°F | Frost possible | Cover plants before dark |
| 29 to 32°F | Light frost likely | Cover well, or harvest ripe and mature-green fruit |
| 28°F or below | Hard freeze | Harvest all mature-green fruit; plants will not survive |
How Does the Check Work?
Tomatoes are damaged as temperatures approach freezing and killed by a hard freeze. The tool compares your forecast low with these thresholds and returns the safest action for the night.
40 to 45°F: cold but no frost, cover tender transplants
33 to 39°F: frost possible on clear calm nights, cover plants
29 to 32°F: light frost likely, cover well or harvest fruit
28°F or below: hard freeze, harvest and expect plant loss
Air temperature is measured a few feet up, but on clear, still nights the ground can be several degrees colder, which is why frost forms even when the forecast is just above freezing.
Worked Example
Say tonight’s low is 34°F on a clear, calm night. The tool warns that frost is possible and tells you to cover the plants before dark with a sheet or row cover. If the low were 26°F, it would call a hard freeze and advise harvesting all mature-green fruit, since the plants will not survive.
Factors That Change the Risk
- Sky and wind: clear, calm nights get much colder at ground level than cloudy or breezy ones.
- Low spots: cold air pools in dips and valleys, so plants there frost first.
- Cover type: row cover or blankets held off the leaves protect better than plastic touching them.
- Containers: potted plants can be moved indoors or into a garage for the night.
- Season stage: late in the season, harvesting green fruit often beats trying to protect tired plants.
Understanding Your Outputs
| Output | Meaning | Best Used For |
|---|---|---|
| Risk verdict | How cold tonight is | Judging urgency |
| Action | Cover, harvest, or relax | Deciding what to do |
| Tip | How to do it | Protecting or picking |
When to Use It
Use it whenever a cold night is forecast, in spring after transplanting or in autumn near the first frost. Pair it with the ripening time calculator for picked green fruit and the temperature checker for planting out.
Common Mistakes to Avoid
- Trusting the exact number: on clear nights, ground frost can form even when the forecast low is a few degrees above freezing.
- Plastic on leaves: plastic touching foliage can worsen freeze damage; hold covers off the plant.
- Covering too late: cover before sunset to trap the day’s warmth.
- Leaving covers on all day: remove them in the morning so plants do not overheat.
- Waiting out a hard freeze: below 28°F, harvest instead of hoping; the plant will die.
Accuracy and Limitations
This is general guidance for frost-tender tomatoes.
What It Tells You: a sensible action from the forecast low.
What It Cannot Know: your exact microclimate, cloud cover, or wind. On clear, still nights, protect earlier than the number alone suggests.
Methodology
Method: the forecast low is compared with frost thresholds for tomatoes, and the safest action is returned. Input Used: forecast low temperature and unit. Thresholds: safe above 45°F; cold with no frost 40 to 45°F; frost possible 33 to 39°F; light frost likely 29 to 32°F; hard freeze at 28°F or below. Guidance: cover before dark, hold covers off the leaves, and harvest mature-green fruit before a hard freeze. Note: on clear, calm nights, ground frost can form even when the forecast low is a few degrees above freezing.
Sources: Iowa State University Extension – Growing Tomatoes, The Old Farmer’s Almanac – Tomatoes, Royal Horticultural Society – Tomatoes. Last reviewed: September 26, 2026 · Reviewed by Aiza Anwar.
Frequently Asked Questions
At what temperature will frost kill tomatoes?
Tomatoes are damaged as temperatures near freezing and killed by a hard freeze at about 28°F or below. A light frost near 32°F harms leaves and exposed fruit but covered plants may survive.
Can tomatoes survive a light frost?
Sometimes, especially if covered. A brief, light frost may only damage the outer leaves, but any frost sets plants back, so cover them or harvest ripe and mature-green fruit.
How do I protect tomatoes from frost?
Cover plants before dark with a sheet, blanket, or row cover held off the leaves with stakes, and remove it in the morning. Move potted plants indoors or into a garage.
Should I pick tomatoes before a frost?
Yes, especially before a hard freeze. Pick all mature-green and ripe fruit and ripen the greens indoors, since frost will damage anything left on the plant.
Does 36°F count as frost for tomatoes?
It can. On clear, calm nights the ground can be several degrees colder than the forecast, so frost can form at a reported low near 36°F. Protect plants to be safe.
Will a sheet protect tomatoes from frost?
Yes, for a light frost. A sheet or blanket traps ground warmth, especially when held off the leaves. For colder nights, add a second layer or use row cover fabric.
Can I move potted tomatoes inside for frost?
Yes. Bring containers into a garage, shed, or house for the night, then return them outdoors once temperatures rise above freezing in the morning.
What do I do with green tomatoes after a frost warning?
Pick the full-size mature-green ones and ripen them indoors at room temperature. Use smaller immature greens in cooked recipes.
Do covers touching the leaves cause damage?
Plastic touching leaves can make freeze damage worse where it contacts them. Use stakes or hoops to hold any cover off the foliage.
Related Tomato Tools
See How Long They Take with the Ripening Time Calculator
This tool gives general frost guidance for tomatoes outdoors. Your microclimate, cloud cover, and wind change the real risk, so protect earlier on clear, calm nights. Below 28°F, harvest rather than protect. Spotted an error? Tell us here.