Frost dates explained, and how to use them
Last reviewed September 2026 · written from public-domain USDA/NOAA data and Cooperative Extension references — see how we source data
Almost every planting decision in a temperate garden is counted forwards or backwards from two dates: the average last frost in spring and the average first frost in fall. Get those roughly right and the rest of the calendar falls into place.
What the dates mean
A frost date is a probability, not a deadline. The commonly quoted "average last frost" is usually the date after which there is only a 50% chance of another 32°F night. There is still meaningful risk for a week or two beyond it.
Conservative gardeners use the 10% date (about two weeks later in spring) for tender crops they cannot afford to lose, and the 50% date for hardy crops and for succession sowings they can replace.
One year, counted from two dates
Finding yours
NOAA publishes freeze/frost "normals" for thousands of US weather stations. Your county Cooperative Extension office also publishes local dates and usually knows the microclimate quirks of the area.
This site's frost date finder uses NOAA-derived state averages as a starting point. Because a state can span a month of variation, entering your own dates from a nearby station is worth the two minutes.
How planting dates are built from them
Start seeds indoors: last frost minus the crop head-start (6–8 weeks for tomatoes, 8–10 for peppers and onions, 3 for cucurbits).
Direct sow hardy crops: several weeks before the last frost, as soon as soil is workable. Direct sow or transplant tender crops: one to two weeks after the last frost, once soil is warm.
Fall crops: first frost minus days to maturity minus a short buffer, working backwards so the crop matures before or just after frost depending on how hardy it is.
Adjusting for your garden
A south-facing slope, a fenced urban yard or a spot near a heated wall can run a week or two ahead of the official date. A frost pocket at the bottom of a hill runs behind it. Keep notes for a season or two and shift your personal dates accordingly.
Frost versus freeze
Official frost dates are based on 32°F measured about five feet above the ground. On clear, still nights the ground and leaf surfaces radiate heat away and can frost when the thermometer on your porch still reads 35 or 36°F - which is why a light frost can catch tender seedlings on a night that never officially dipped to freezing.
A light frost (around 30-32°F) kills the tender crops - tomatoes, peppers, basil, beans, squash, cucumbers. A hard freeze (about 28°F and below, for several hours) is what finally stops hardy crops like cabbage, broccoli and lettuce. Kale, spinach, parsnips and leeks shrug off even that, and many taste sweeter after it.
Protecting plants when frost is forecast
Cover tender plants in the late afternoon while the soil still holds the day's warmth, and uncover them the next morning once temperatures climb. Floating row cover gives a few degrees of protection per layer; old sheets and buckets work in a pinch. Keep plastic from touching leaves - it conducts cold straight through.
Water the soil the day before a cold night. Moist soil stores and releases more heat than dry soil. For crops you are extending into fall, a low tunnel of hoops and row cover can add weeks - see season extension.
When the forecast and the average disagree
Averages tell you when to plan; the ten-day forecast tells you when to plant. If your last frost date has passed but a cold, clear, windless night is forecast, wait or be ready to cover. Equally, a warm spring doesn't mean tender crops can go out a month early - the soil is usually still too cold for them to grow even if the air is mild.
Using your dates on this site
Once you know your dates, the planting calendar builds every indoor-sow, transplant and harvest window from them, and the seed starting calculator lists what to start indoors each week. The When to plant pages show the same calculation worked out for popular crops in every state.
Common questions
Is the last frost date the same as the safe planting date?
Not for tender crops. The usual average last frost date still carries about a 50% chance of a later frost. For tomatoes, peppers and other tender plants, waiting until about two weeks after it cuts the risk to roughly 10%.
What temperature counts as frost?
Officially 32°F at about five feet above ground. On clear, calm nights plants at ground level can frost when the air above them is still a few degrees warmer.
Can I plant anything before my last frost date?
Yes. Hardy crops like peas, spinach, lettuce, onions and radishes are normally sown two to six weeks before the last frost, as soon as the soil can be worked.
Do frost dates change over time?
Yes. NOAA recalculates its climate normals every ten years from the latest 30 years of data, and in many parts of the US the frost-free season has lengthened. Local notes from your own garden are still the best guide.