Growing Degree Days by Zip Code Map
Plants and pests don’t run on the calendar — they run on accumulated heat. Growing degree days (GDD) measure that heat, and they predict when crops mature, when pests emerge, and when blooms open far better than a date on the calendar does. This map gives you the average growing degree days for your ZIP code so you can gauge how much warmth your season delivers.
How to use the map: enter your ZIP code in the search box below to see the average growing degree days that accumulate over your season. Higher numbers mean a longer, warmer growing window; lower numbers mean a short, cool season that favors quick-maturing varieties.
Growing Degree Days
Average GDD, base 50 F
Monthly Rainfall
Growing degree day totals on this map are calculated from a 30-year average of climate data from 1991 to 2020, which gives you a stable baseline rather than one unusual year. Treat the number as a normal season; a hot year runs higher and a cool year lower. Microclimate matters too — a sheltered, south-facing site accumulates more heat than an exposed or shaded one.
Growing degree days are one climate filter. Pair them with your USDA hardiness zone, AHS heat zone, and frost dates (last and first) for the full picture.
What Are Growing Degree Days?
A growing degree day is a single day’s worth of heat above the temperature at which a plant starts to grow. Add up those daily units across the season and you get accumulated growing degree days — a running measure of how much warmth a crop has received. Because development is driven by heat, GDD predicts growth stages, pest life cycles, and harvest timing more reliably than the date.
How to Calculate Growing Degree Days
The standard formula is simple: take the day’s high and low temperature, average them, and subtract a base temperature below which the plant doesn’t grow.
GDD = ( (daily high + daily low) ÷ 2 ) − base temperature
If the average falls below the base temperature, that day scores zero rather than a negative number. The base temperature depends on the crop: 50°F is the most common (used for corn and many warm-season crops), while cool-season crops often use 40°F or 41°F. Daily values are added together to give the season’s accumulated total.
How to Use Growing Degree Days in the Garden
- Predict harvest and bloom. Many crops and varieties list the GDD they need to mature, so you can estimate timing from accumulation rather than a guessed date.
- Time pest control. Insect pests emerge at predictable GDD thresholds, which is why GDD models drive much of modern integrated pest management.
- Match varieties to your season. A low seasonal total favors short-season, quick-maturing varieties; a high total opens up long-season, heat-loving crops.
- Compare your site year to year. Tracking accumulation against the average tells you whether your season is running ahead of or behind a normal year.
Growing Degree Days vs Calendar Dates
The same calendar week can deliver very different heat from one year to the next, and from one ZIP code to the next. That is why “plant after May 15” or “spray in late June” so often misses: a cool spring slows everything down and a warm one speeds it up. GDD tracks the heat itself, so it stays accurate when the calendar does not.
How Accurate Is a Growing Degree Days Map?
The map gives a reliable seasonal average, but any single year runs hotter or cooler, and your exact site can accumulate more or less heat than the regional figure. Use it to compare your area’s heat budget and choose varieties; for precise pest timing, track GDD from a nearby weather station through the season.
What are growing degree days?
Growing degree days (GDD) are a measure of accumulated heat above a base temperature, used to predict plant growth, bloom, pest emergence, and harvest timing. They track development by heat rather than by the calendar.
What is a growing degree day?
One growing degree day is a single day’s amount of heat above the base temperature a plant needs to grow. Each day’s value is the average of the high and low temperature minus that base, with negatives counted as zero.
How do you calculate growing degree days?
Average the day’s high and low temperatures, then subtract the base temperature: GDD = ((high + low) / 2) – base. If the result is negative, count it as zero. Add each day’s value together for the season’s accumulated total.
What base temperature should I use?
It depends on the crop. 50°F is the most common base and suits corn and many warm-season crops, while cool-season crops often use 40°F or 41°F. Use the base that matches what you are growing.
How do I find growing degree days for my area?
Use the map and ZIP lookup above for your average seasonal accumulation. For live, in-season tracking, many state extension services and weather networks publish daily GDD from local stations.
How accurate is a growing degree days map?
It is a dependable 30-year average, but any single season runs warmer or cooler, and your specific site can differ from the regional number. Use it for variety selection and planning, and track a local station for precise pest timing.
Sources and Further Reading
- NOAA 1991–2020 U.S. Climate Normals — the temperature base data behind these GDD totals.
- University extension integrated pest management (IPM) programs — standard sources for GDD models and base temperatures.
Next step: match your seasonal heat to plants that fit your whole climate. Use the Plant Finder, or pair this with the hardiness zone map, heat zone map, and last frost date map.