How to find your frost dates
Most planting tools start from two numbers: your average last spring frost and your average first fall frost. Here's what they mean and where to get reliable ones.
Two dates that run your garden calendar
Last spring frost anchors the seed starting calculator: you count back to start seeds indoors and forward to set tender plants out. First fall frost anchors the fall planting calculator: you count back to find the last date a crop can still mature.
Where to look them up
- NOAA climate normals. NOAA's National Centers for Environmental Information publish the official 1991–2020 U.S. Climate Normals. Their interactive map lets you search by station, ZIP code, city, county or state and includes frost and freeze dates.
- Your state extension service. Land-grant universities publish local planting calendars and frost guidance — for example, UNH Extension notes Memorial Day as a conservative last-frost estimate for central New Hampshire.
- Your own records. A cheap min/max thermometer and a garden notebook beat any regional average after a few seasons.
Don't use your hardiness zone for timing
USDA hardiness zones are built from average annual extreme minimum winter temperatures. They are useful for choosing perennials, but they don't tell you when spring frosts end.
Average means "not guaranteed"
An average date is a midpoint of past years, so some years will frost later. Keep row cover or old sheets ready and check the forecast before setting out tomatoes, peppers and squash.
Frequently asked questions
What is the average last frost date?
The date in spring after which frost becomes unlikely, based on historical temperature records for a location. Because it is an average, frost still occurs after it in some years.
Is my hardiness zone the same as my frost date?
No. The USDA Plant Hardiness Zone Map is based on the average annual extreme minimum winter temperature. It tells you which perennials survive winter, not when spring frosts end.
Where can I look up frost dates?
NOAA's U.S. Climate Normals include frost and freeze dates, searchable by station, ZIP code, city or county through NOAA's interactive normals map. Your state extension service also publishes local planting calendars.