About the data

Every number on this site comes from public records. Nothing is a forecast.

Frost dates

NOAA's U.S. Climate Normals for 1991 to 2020 include freeze statistics for each weather station: the dates by which the last spring and first fall 32°F and 28°F temperatures occur with 10%, 50% and 90% probability, and the length of the frost-free season. We use the annual and seasonal normals, version 1.0.1.

The "average last frost" on each page is the 50% date. Half of years have another frost after it, which is why we also show the 10% date: frost after that happens about one year in ten.

Cities and stations

We include US places with at least 20,000 residents from the Census Bureau, 2,330 in all, and match each to the nearest NOAA station with freeze data within 30 kilometers. That is 1,231 stations. Each city page names its station and the distance, so you can judge how well it fits your yard.

Some stations, mostly in Southern California, South Florida and Hawaii, see a freeze in fewer than half of years. NOAA publishes no frost date for them and neither do we.

Planting windows

Windows are counted in weeks from the average last frost (spring crops) or first frost (fall crops and bulbs). The offsets follow the frost-based timing used in extension planting guides, including Iowa State University's Planting and Harvesting Times for Garden Vegetables, University of Minnesota Extension and the Texas A&M AgriLife vegetable planting guide.

Warm-season crops never go out before February 15, even where frost ends in January, because nights are still too cool for them to grow. A few more crops get special handling. Garlic and daffodils in mild-winter places are set to October and November, and tulips there to late December after pre-chilling. In frost-free places we skip the calendar, because heat rather than cold sets the timing.

Limits

A station can sit miles away and hundreds of feet higher or lower than your garden. Valleys collect cold air; slopes and cities stay warmer. Use these dates to plan, then check the ten-day forecast before setting out tender plants.

Questions or corrections: [email protected].