Growing Degree Days

How does temperature impact growth of plants and organisms?

There is a science to every service we perform at Ahlum & Arbor and each year brings a new challenge called Growing Degree Days (GDD). There is a certain temperature threshold for plants and insects that determines their growing season. GDDs help us know when things are budding out or blooming and when insects are hatching or actively feeding on your plants. 

Without diving too much into the calculations, GDDs are calculated for a specific day by comparing the mean temperature to the base temperature for a specific organism. Growth and development for each organism or plant will only occur if the day’s temperature is higher than the minimum temperature it needs to grow. GDDs are labeled due to temperatures not reaching the desired threshold for growth. As temperatures rise so do growth and development and vice versa. This year, on April 28 the GDD was 255 whereas in 2021 it was 323. 

Each organism’s temperature threshold is different, requiring research and experimentation. This is a proven reliable method of tracking and knowing when insects are active, compared to the normal calendars we use to track our days. 

Plant Health Care Technician tending to the growth of a shrub and comparing temperature data.

How are GDDs impacting this year’s growth?

In 2022, Ohio has had an increased number of GDDs, where temperatures have not reached or sustained their normal height. These lower temperatures have caused a shift in our planning of insecticide and fungicide treatments. Without the growth of new buds or hatching of insects it causes our teams to push their treatments back for when they will be most effective. 

This year, we have been experiencing quite frequent overnight freezing temperatures, or near freezing. These huge temperature changes have caused a large division between when different trees are leafing out compared to other years. While these temperature shifts have caused us to push our treatments back, we are feeling hopeful for the coming weeks.