What are Growing Degree Days and What Do They Mean for the Sustainable Agriculture Team?

Spring is slowly but surely arriving at the farm! As many of you might have noticed, we’ve had a cold and overcast spring. In response, your spring bulbs, garlic, trees and shrubs, and vegetable plants might be growing more slowly than last year. 

Plants develop in response to temperature (among other factors). Farmers and researchers use a special way to track daily heat units and thus more accurately predict crop development. Growing Degree Days (GDD) track the accumulation of average daily temperatures. Each crop has a different minimum temperature threshold that must be exceeded for growth to occur. Cool-season crops like lettuce have a lower temperature threshold for development than warm-season crops like tomatoes. 

In 2022, we’ve had 43 GDD (temperatures over 50 F). In comparison, we had 131 GDD (temperatures over 50F) last year. That’s a huge difference!

Are we having a cooler than average spring, or was last year just really warm? Both! Looking back at historical data, the previous six years’ GDD average is 58. So it is a cooler spring this year than on average, but last year was well above average.

So what does this mean for farmers and gardeners? A spring with less GDD means slower development of crops, so you should be prepared for your plants to be 1-2 weeks behind a warmer spring. Seeds will take longer to germinate, develop and be ready to harvest.

Is there anything I can do? When planting crops outside, add a layer of row cover on top to raise the temperature around the transplants. And wait to put out hot weather crops like squash, cucumbers, tomatoes, peppers, and eggplant until we see temperatures consistently above 55 F and ideally above 75 F.

For more information on Growing Degree Days, check out this article. You can track GDD using MSU’s Enviroweather website.

This entry was posted in Happenings. Bookmark the permalink.