Last / First Frost Lookup

How to use the frost lookup

This lookup is the quick reference version of the frost calculator: pick a zone and get its average last spring frost and first autumn frost, or scan the full table to compare zones. The two dates are the ones every planting decision hangs on. The last spring frost tells you when tender plants can go outside; the first autumn frost tells you when the season ends for them. The gap between the two is your frost-free growing season, and it varies enormously — from roughly six weeks in zone 1 to year-round in zones 11 to 13.

Reading the table

The winter low column is the definition of the USDA zone itself: each zone is a 10°F band of average annual minimum temperature, so zone 7 means winter lows typically fall between 0 and 10°F. That band is about plant survival in winter, not about frost dates, but the two track together — colder zones have later last frosts and earlier first frosts. Notice how the season compresses as you go north: zone 8 enjoys a season of roughly eight months, zone 4 about four and a half, and zone 2 barely three. That compression is why northern gardeners lean on indoor seed starting, season extension and fast-maturing varieties, while southern gardeners plan around summer heat as much as frost.

The frost columns are ranges, not single dates, because frost does not arrive on a schedule. A range like “April 15–May 1” means the last frost has typically fallen somewhere in that window over many years of records. In a warm year it may come at the start of the range; in a cold year, at the end — or even beyond it. This is not a flaw in the data; it is the weather. Use the range as a planning window and the forecast as the final word. If you are comparing two zones — say you are moving, or choosing between varieties — the table shows at a glance how much season you gain or lose.

From lookup to planting plan

Once you know your two frost dates, you can build a whole season around them. Count backwards from the last frost for indoor seed starting: tender crops such as tomatoes and peppers start six to eight weeks before it, hardy crops four to six. Count forwards from the last frost for transplanting tender crops out — and add a week or two of margin, because planting on the average date is a coin flip. Count backwards from the first frost for autumn crops: most need at least eight weeks of growth, so their last sowing date is roughly eight weeks before the first frost range begins. And check days to maturity against the season length before committing to a long-season crop: a squash needing 110 days will not ripen if your frost-free season is only 100 days, however warm the summer is.

When the table is not enough

Zone averages smooth over real differences. A garden at the bottom of a hill collects cold air and can frost weeks after a garden on the slope above it; a walled city garden can run a full zone warmer than the countryside around it; a coastal garden rarely sees the sharp frosts an inland garden at the same latitude gets. Elevation is the biggest single factor after latitude — in mountain regions, every few hundred feet of elevation can shift frost dates by a week. That is why the USDA map and the extension service matter: they work at county and local level, while a zone number works at continental level. Keep your own notes of first and last frost each year — a cheap min–max thermometer by the beds is enough — and within a few seasons you will have frost dates for your garden that beat any table.

Related tools: the Frost Date Calculator adds season length and planning markers for your zone, the Hardiness Zone Finder helps you find your zone from your state, and the Seed-Starting Calculator turns your last frost date into indoor sowing dates. Browse the planting calendar hub for zone-by-zone monthly pages.