Growing degree days

Growing degree days (GDD) accumulate warmth: each day's average temperature above a base (often 50°F), summed through the season. Corn breeders rate varieties in GDD to maturity rather than days because calendar days mean different things in different climates. Home gardeners mostly use days-to-maturity plus frost dates, but GDD explains why the 'same' tomato ripens earlier in Tulsa than Traverse City.

See also: Days to maturity · Growing season