Weather Words: Growing Degree Days

As spring planting gets underway, from the smallest household vegetable gardens to the large-scale farms, growing degree days matter.

Growing degree days (GDD) measure heat accumulation over time to estimate plant and insect development. Instead of just counting calendar days, GDDs track how much warmth a location has received, because that’s what really drives biological growth.

For an example, we’ll start with plants that need an average temperature above 50 degrees to grow. A day that hits 60 degrees would be considered 10 GDD, anything at or below 50 degrees wouldn’t be a GDD, or would be marked as zero.

GDD are also used to track pollen season and pests. The more GDD an area experiences could lengthen pollen season and keep pests around longer.

According to Climate Central, we are now seeing more GDD across the country due to climate change. While some plants benefit from more GDD, the warmer days can also lead to higher evaporation rates and create more drought conditions - which leads to stress on plants and crops.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.