Learn More About Growing Degree Days

Plant development is largely driven by heat accumulation.  Growing Degree Days (GDD) are a measure of heat accumulation and can be correlated to plant development.  The GDD scale is a better measure of plant development than calendar date because GDD required to reach a certain growth stage is constant and calendar date is not.

For example, in Winnipeg Manitoba in 2003, 560 GDD had already accumulated by May 30th, but in 2004, the same amount of GDD had not accumulated until June 10th.  If wheat had been seeded on May 15 in both years, it would have reached the 3rd tiller stage by May 30 in 2003, but would have only reached that stage by June 10 in 2004.  In other words, it always takes 560 GDD to reach 3 tillers, but it doesn't always take 2 weeks.

How To Calculate GDD's

GDD = ((Temperature_max + Temperature_min)/2) - Temperature_base

Max and Min refer to the daily maximum and minimum temperature on a given day.  Base temperature is the minimum temperature at which a plant grows and develops.  Different base temperatures are used for different crops.  For most cool season crops, a base of zero degrees is used, for potatoes, 7 degrees is used and for corn, 10 degrees is used.  GDD's are calculated for each day and added to one another to calculate the amount accumulated up to a certain date.

Learn how indicator plants can determine crop development.

Copyright © 2005.  Gary Martens.  All rights reserved.

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