Frost Date Calculator

How to use frost dates in the garden

Frost dates are the two bookends of the gardening year. The last spring frost is the date after which tender plants can usually go outside safely; the first autumn frost is the date that usually ends the season for them. Everything between those two dates is your frost-free growing season, and almost every planting decision — when to start seeds, when to transplant, what will ripen in time — is counted forwards from the spring date or backwards from the autumn one. This calculator gives you both dates for any USDA zone, plus the length of the season between them.

What “average” really means

The dates here are averages drawn from USDA and NOAA records, and they are shown as ranges for a reason. An average last frost of “April 1–15” does not mean frost ends on a particular day: it means that over many years, the last frost has typically fallen somewhere inside that window. In any single year it can be two weeks early or two weeks late, and a garden in a frost pocket — a low spot where cold air pools — can freeze when a garden on a slope a street away does not. The mid-point dates this tool uses for its season-length maths are just the middle of the range, a convenient anchor for counting weeks, not a forecast.

The practical consequence is simple: do not plant tender crops on the average date. Gardeners who do lose plants roughly half the time. Wait a week or two past the average, watch the short-term forecast, and keep frost protection — row cover, cloches or even an old bed sheet — within reach for the first few weeks after transplanting. A single night at or below freezing kills tomatoes, peppers, cucumbers and squash outright, and even a light frost can set them back for weeks. Hardy crops are different: peas, lettuce, spinach, radishes and brassicas tolerate light frosts and can be sown weeks before the last frost date, which is how cold-climate gardeners get a harvest while tender crops are still indoors.

Using the season length

The frost-free season length tells you what is realistic in your zone. A 90-day season means long-season crops such as winter squash and sweet potatoes are a stretch unless you start them indoors or choose the fastest-maturing varieties; a 200-day season means you can fit in a spring crop, a summer crop and an autumn crop in the same bed. To check whether a crop will ripen, add its days to maturity to your sowing or transplant date and compare the result with the first frost range — if the harvest date lands after the first frost, pick a faster variety or start earlier. The eight-week marker in the results is a handy rule of thumb for autumn sowing: most autumn vegetables need at least eight weeks of growth before frost, so sow them no later than eight weeks before the first frost range begins.

Frost, freeze and hard frost

Not all frosts are equal. A light frost (29–32°F / −2–0°C) kills tender leaves but leaves hardy crops standing. A hard freeze (below 28°F / −2°C for several hours) ends the season for almost everything except the hardiest brassicas and root crops. The “frost date” in the records generally means the last (or first) night at or below 32°F, so even after the last frost date has passed, a late cold snap is possible — it is just less likely. Microclimate matters more than most beginners expect: soil near a south-facing wall, raised beds and urban gardens all run a few degrees warmer, while low spots and open fields run colder. Keep a simple record of your own first and last frosts each year; after two or three seasons you will have dates tuned to your garden, which are worth more than any zone average.

Related tools: look up every zone at once with the Last / First Frost Lookup, plan your month with the Garden Planner, work out indoor sowing dates with the Seed-Starting Calculator, and find your zone with the Hardiness Zone Finder. For zone-by-zone planting pages, browse the planting calendar hub.