Practical planning tools for short growing seasons.

Map-style climate resource

U.S. Garden Climate Atlas

A visual guide to frost-free days, seasonal crop heat, and growing-season pressure across U.S. cities in the GrowByDate dataset.

Updated 2026-06-05 · 243 U.S. cities across 24 states with both frost and GDD reference data.

Median frost-free season 161 days Median across the U.S. cities in the atlas.
Median base-50 GDD 2316 Median seasonal heat accumulation across U.S. cities.
Core lesson Time ≠ heat A longer frost-free season does not always mean a warmer crop season.

Outdoor window

Frost-free days show how long tender crops usually have outside.

A shorter frost-free window pushes gardeners toward fast varieties, transplants, frost protection, or more conservative crop choices.

Crop heat

GDD shows how much warmth accumulates inside that window.

Warm-season crops such as tomatoes, peppers, squash, corn, okra, and melons need more than calendar time. They need usable heat.

Climate point map

U.S. frost-free season by city

Points are positioned by city latitude and longitude. Larger, warmer-coloured points represent longer frost-free windows.

Very short Under 100 days Short 100–129 days Moderate 130–159 days Long 160–189 days Very long 190+ days

Climate point map

U.S. base-50°F GDD by city

Same city positions, different signal. Larger, warmer-coloured points represent higher seasonal heat accumulation.

Very cool Under 1,000 base-50 GDD Cool 1,000–1,499 Moderate heat 1,500–1,999 Warm 2,000–2,499 High heat 2,500+

Climate leaders and pressure points

The fastest read is often in the extremes: which places have the most outdoor time, which places are most compressed, and which places accumulate the most usable crop heat.

State summary

Median values are calculated from the U.S. cities currently included in the GrowByDate dataset.

State Cities Median frost-free days Median base-50 GDD Longest-season city Highest-GDD city
Colorado 13 156 2540 Grand Junction Grand Junction
Idaho 10 148 2221 Lewiston Boise
Illinois 8 191 3413 Quincy Carbondale
Indiana 7 184 3435 Evansville Evansville
Iowa 11 166 2840 Davenport Council Bluffs
Kansas 7 188 3900 Wichita Wichita
Maine 7 153 2035 Lewiston Portland
Massachusetts 4 172 2671 Boston Boston
Michigan 19 159 2371 Detroit Detroit
Minnesota 21 151 2030 Winona Winona
Missouri 7 206 3981 St. Louis St. Louis
Montana 13 137 1465 Great Falls Sidney
Nebraska 8 168 3102 Omaha Omaha
New Hampshire 7 148 1931 Manchester Portsmouth
New York 11 162 2316 Buffalo Albany
North Dakota 12 138 1927 Grafton Fargo
Ohio 6 190 3196 Cleveland Cincinnati
Oregon 12 194 2161 Portland Medford
Pennsylvania 6 188 2900 Erie Pittsburgh
South Dakota 6 147 2224 Sioux Falls Sioux Falls
Vermont 5 143 1768 Burlington Burlington
Washington 14 217 1905 Port Angeles Wenatchee
Wisconsin 20 162 2269 Kenosha Milwaukee
Wyoming 9 125 1953 Cheyenne Riverton

How to use the atlas

Frost-free days estimate the outdoor window for tender crops. Base-50°F GDD estimates how much crop heat accumulates during the season. For warm-season crops, the best planning read comes from comparing both signals together.

  • Use the frost-free map to compare outdoor season length.
  • Use the GDD map to compare seasonal heat for crops such as tomatoes, peppers, corn, squash, okra, and melons.
  • Use Long Season vs Warm Season to understand why the two signals are not interchangeable.

Share, cite, or reference this atlas

Use the atlas when writing about U.S. garden climate, frost-free season length, growing degree days, or crop planning across northern and temperate states.

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Methodology and limits

This atlas joins city frost-date records with base-50°F GDD reference records. Frost-free days are calculated from average last spring frost and first fall frost. GDD values represent seasonal accumulated crop heat from the mapped station series. These values are planning averages, not site-specific forecasts. Current U.S. coverage is based on the cities and states available in the GrowByDate dataset.

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