Updated October 28, 2026
Your average last spring frost date anchors every vegetable garden calendar. Enter it and see when to sow indoors, when to move seedlings outside and when to sow straight into the ground.
Open the calculator ↓Seed-starting charts count weeks before or after the last frost. This tool turns them into calendar dates.
Method: transplant and sowing dates are your frost date (plus the safety margin) moved by the weeks in the University of New Hampshire (UNH) Cooperative Extension chart "When to Plant your Vegetable Garden" (2016). Indoor start dates count back by the chart's weeks from seed to transplant. Other charts differ by a week or two; check the seed packet too.
The USDA Agricultural Research Service (ARS) released the current Plant Hardiness Zone Map in November 2023, with the PRISM Climate Group at Oregon State University. It replaced the 2012 map.
Each zone is based on the average annual extreme minimum temperature: the coldest night of the winter, averaged over 1991 to 2020. The map has 13 zones. Each zone covers 10°F and splits into two 5°F half zones, “a” (colder) and “b” (warmer).
ARS reports that about half of the country moved one half zone warmer than in 2012; the rest stayed in the same half zone. Christopher Daly, director of the PRISM Climate Group, says the 2023 map is about 2.5°F warmer than the 2012 map across the contiguous United States.
A hardiness zone answers one question: will a perennial, shrub or tree survive a typical winter here? It does not give a frost date. Two towns in the same half zone can have last frost dates weeks apart because of elevation, distance from water and local terrain.
Find your zone with the interactive map on the USDA ARS website by ZIP code. For frost dates, ask your state's Cooperative Extension office, which bases its charts on NOAA climate normals for nearby weather stations.
An average last frost date is not a promise. It marks the point where a spring frost (32°F) is about as likely to come later as it is to come earlier. On the average date itself, there is still roughly a 50 percent chance of another frost.
That is why the calculator has a safety margin. Frost-hardy crops such as peas and spinach do not care. Tomatoes, peppers and basil are damaged by a light frost, so many gardeners add one or two weeks before they transplant them.
Indoor seedlings have not felt wind, direct sun or cool nights. Over 1 to 2 weeks, set them outside a few hours a day and add time step by step.
UNH Extension fact sheets say beans do not germinate well below 60°F soil, and sweet corn needs at least 50°F, with 60°F or warmer ideal. University of Minnesota Extension lists about 65°F for most supersweet corn varieties.
Every crop in the calculator falls into one of two groups. The group tells you which side of the frost date it belongs on. Timings are from the UNH chart.
No. The 2023 USDA Plant Hardiness Zone Map is based on the average coldest winter night from 1991 to 2020. It tells you which perennials survive your winter. Frost dates come from local climate records, so two towns in the same zone can have last frost dates weeks apart.
It is the date after which a spring frost becomes less likely than not. On average there is still about a 50 percent chance of frost after it, so many gardeners wait one or two weeks more before they set out tender crops.
They come from the University of New Hampshire Cooperative Extension planting chart (2016): the weeks before or after the last frost when each crop is safe to set out, and the weeks each transplant needs from seed. Other extension charts, seed packets and your local extension office may give slightly different numbers.
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