What is a growing degree day?

A GDD is a daily heat unit above a crop-specific base temperature. Corn uses base 50°F/10°C; wheat uses 32°F/0°C; grapes and many perennials use base 50°F. Sum them from planting or bud-break, and each phenological stage occurs at a roughly fixed GDD accumulation.

Why does GDD matter operationally?

Because it predicts stage timing better than calendar days. Silking, veraison, harvest windows, and pest-generation timing all track GDD accumulation, not the date. Warmer springs push each stage earlier — sometimes by two weeks.

How is climate change affecting GDD accumulation?

Most US growing regions have gained 100–300 GDD per season since the 1980s. That accelerates every stage, compresses the harvest window for some crops, and — for perennials — can push veraison or bloom into a heat-stress window.

Are more GDD always better?

No. For cool-season crops (peas, small grains, cool-climate grapes) and for chill-dependent perennials, more GDD means more heat stress and less chill accumulation. The right answer is always crop- and cultivar-specific.

Growing degree days explained: crop thresholds, warming, and drift.

Growing degree days.

The operating clock of the growing season. Here's how it's built, why it's shifting, and what the shift is doing to every stage of your calendar.

The daily calculation

GDD = max(0, (Tmax + Tmin)/2 − Tbase). Sum daily values from planting or bud-break to the stage you care about. Each crop has a characteristic accumulation target for each stage.

Rough targets by crop

Corn (Tbase 50°F): ~2,700 GDD to physiological maturity for a full-season hybrid.
Soybean: ~2,600 GDD to R7 for a mid-maturity variety.
Winter wheat: ~2,000 GDD from spring greenup to harvest.
Wine grapes: ~1,800–2,200 GDD from bud-break to harvest depending on variety.

What ArchipelAI gives you

Every field's report in the Agriculture workspace includes projected GDD accumulation with 20-year trajectory. Try it in the agriculture demo.

Common questions

What is a growing degree day?: A GDD is a daily heat unit above a crop-specific base temperature. Corn uses base 50°F/10°C; wheat uses 32°F/0°C; grapes and many perennials use base 50°F. Sum them from planting or bud-break, and each phenological stage occurs at a roughly fixed GDD accumulation.
Why does GDD matter operationally?: Because it predicts stage timing better than calendar days. Silking, veraison, harvest windows, and pest-generation timing all track GDD accumulation, not the date. Warmer springs push each stage earlier — sometimes by two weeks.
How is climate change affecting GDD accumulation?: Most US growing regions have gained 100–300 GDD per season since the 1980s. That accelerates every stage, compresses the harvest window for some crops, and — for perennials — can push veraison or bloom into a heat-stress window.
Are more GDD always better?: No. For cool-season crops (peas, small grains, cool-climate grapes) and for chill-dependent perennials, more GDD means more heat stress and less chill accumulation. The right answer is always crop- and cultivar-specific.

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