Calculate Growing Degree Units (GDU) or Growing Degree Days (GDD) for crop management. Track heat accumulation to predict crop development stages.
Last updated: March 2026
Corn/Soybeans: 50°F, Wheat: 32°F, Cotton: 60°F
Growing Degree Units (GDU), also called Growing Degree Days (GDD) or Heat Units, measure heat accumulation over time to predict plant and insect development. Unlike calendar days, GDU account for the actual thermal energy available for growth, making them far more accurate for predicting crop stages.
Plants require a certain amount of heat to progress from one developmental stage to the next—germination, emergence, flowering, maturity. Each crop has a base temperature below which growth essentially stops and an optimal temperature range. GDU accumulate only when temperatures exceed the base temperature, and growth typically plateaus above 86°F for most crops.
Farmers use GDU to time planting, predict harvest dates, schedule pesticide applications, and select appropriate crop varieties for their climate. Agronomists have established GDU requirements for every major crop—for example, corn typically needs 2,400-2,900 GDU from planting to maturity depending on the hybrid.
Calculate GDU for corn on a warm summer day:
This day accumulated 20 GDU toward corn maturity. A typical corn hybrid requiring 2,600 GDU would need 130 such days to reach maturity. In practice, GDU accumulation varies daily with weather. Track cumulative GDU from planting to predict when the crop will reach key growth stages.
Crop development is driven by temperature, not time. A cool spring delays growth; a warm spring accelerates it. Calendar days can't predict this, but GDU can, making harvest predictions accurate within days.
For annual crops, start counting from planting date. For perennials, start from a specific date (often January 1) or when consistent warm temperatures begin. Reset the count each growing season.
GDU for that day = 0. Growth essentially stops below the base temperature. This is why corn planted in early spring doesn't emerge until soil temperatures consistently exceed 50°F.
Yes! The formula works identically. For corn in Celsius: GDU = (Max + Min) / 2 - 10°C (with Max capped at 30°C). The numerical GDU values will differ but progression remains accurate.
Seed companies list GDU requirements for each hybrid on seed packaging and websites. Extension offices publish crop-specific GDU requirements. For example, corn ranges from 2,200 GDU (short season) to 3,000+ GDU (full season).
Most crops' photosynthesis and growth rates plateau around 86°F (30°C) and decline above that due to heat stress and increased respiration. Including higher temperatures would overestimate actual growth.
Very closely. For corn, maturity occurs within 3-5 days of reaching the hybrid's GDU requirement. Weather during grain fill can cause slight variations, but GDU is far more accurate than calendar days.
Absolutely. Insects are also heat-dependent. For example, corn borers, Japanese beetles, and many pests emerge at predictable GDU thresholds. This helps time pesticide applications precisely when insects are vulnerable.
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