Your Frost Dates Shape Everything You Can Grow

Every location in the continental US has two critical dates: the average last spring frost and the average first fall frost. The gap between them — your frost-free growing season — determines which crops can complete their lifecycle outdoors.

A tomato needs 70-90 frost-free days to fruit. Sweet corn needs 60-100. Winter squash needs 80-120. If your frost-free season is only 100 days, long-season varieties won't mature before the first fall freeze kills the plant. Short-season varieties — bred specifically for northern climates — can produce within that window.

NOAA publishes frost date estimates based on 30 years of temperature observations from weather stations across the country, interpolated into continuous raster surfaces. These are statistical probabilities, not fixed calendar dates.

The frost-free growing season varies dramatically across the US, driven by latitude, elevation, proximity to water, and regional climate patterns:

90–130 days

Short Season

Northern tier states (MN, WI, ME, MT) and high elevations. Fast-maturing varieties are essential. Season extension (row covers, cold frames) can add 2-4 weeks on each end.

150–200 days

Moderate Season

Mid-Atlantic, Midwest, and Pacific Northwest. Most standard vegetable varieties mature comfortably. Succession planting allows multiple harvests.

240–365 days

Long / Year-Round

Deep South, Gulf Coast, Southern California, and Florida. Year-round growing possible. Heat tolerance becomes the constraint instead of frost.

Pick your state for its frost window, then your county for the local 28°F hard-freeze dates — closer to your own ground than a statewide range, and a step toward the frost date at your exact address.

Most gardening websites provide frost dates by ZIP code. The problem: ZIP codes are mail delivery routes, not climate zones. A single ZIP code can span valleys and hilltops with frost date differences of 2-3 weeks.

• Elevation: Cold air pools in valleys. A parcel at the bottom of a slope can frost 2-3 weeks later in spring and 2-3 weeks earlier in fall than one at the top — even within the same ZIP code.
• Urban heat island: Cities retain heat from pavement and buildings. Urban parcels may have frost-free seasons 1-2 weeks longer than rural parcels at the same latitude and elevation.
• Water proximity: Large water bodies moderate temperature extremes. Parcels near the Great Lakes, ocean coastlines, or large rivers often have delayed spring warming but also delayed fall frost — shifting the growing window later in both directions.

NOAA's raster data captures these spatial gradients at 800m resolution, providing frost estimates that account for the local landscape rather than averaging across a ZIP code.

Pro Tip

Row covers and cold frames can extend your season by 2-4 weeks on each end. If you're 10 days short of growing a longer-season crop, season extension may be all you need.

Growable Ground extracts frost dates from NOAA NCEI 30-year climate normal rasters at your parcel's exact coordinates. These dates feed into multiple scoring dimensions:

• Frost-free season length: The number of days between last spring frost (50% probability) and first fall frost. Crops that need more days than your season provides score lower.
• Planting calendar: Your last spring frost date anchors the planting schedule. "Start indoors 6 weeks before last frost" becomes a specific calendar date for your location.
• Growing degree day accumulation: Frost dates define the start and end of the heat accumulation window. GDD (from PRISM climate data) measures whether enough warmth accumulates during your frost-free period for crops to mature.
• Frost pocket detection: Growable Ground uses USGS elevation data to identify parcels at the bottom of terrain depressions — frost pockets where cold air collects. These locations may experience frost dates outside the regional average.