Lack of growing degree days means slow spring green up
All seasonal plants need consistent warmth and daily average temperatures above 50 degrees in order to break their buds, green up and flower. Growing degree days is the unit that measures the accumulation of those warm temperatures. It is interesting, because each species of plants and trees needs a certain amount of heat, or growing degree days, to bloom.
This year we have had a low number of growing degree days, meaning not a lot of days with an average temperature over 50 degrees. Specifically, we have only had 36, which is much lower than how many we should have by now, around 112.
The low growing degree day value explains why it is taking the leaves so long to grow on our trees. The leaves are currently 20 days later than normal.
April 2018. No green shown from satellite in the Great Lakes region
April 2017. More green showing across the Midwest and Great Lakes region
This is not completely uncommon, but the last time we have waited so long for leaves was five years ago in 2013. In 2016 and 2017, we had many more growing degree days by the end of April, and therefore, it was looking a lot more like Spring.
Growing Degree Day values
