Down the Garden Path

Richard Hentschel, Extension Educator

Plants in the garden (and insects too) develop based on something called "Growing Degree Days" or GDD for short. This is an accumulation of heat units using a base of 50 degrees. For every degree above fifty goes towards the growing degree-days and plant development. Most of us do not follow GDD, but rely on the catalog or seed packet information on how long it takes to go from seed to harvest. You will see a variety listed as a short or long season plant. Those that have grown sweet corn are very familiar with these terms. The same can be said for tomatoes.

It has been an interesting spring and early summer watching the recorded numbers and comparing them to the historical averages. The sample below is indicating that the St. Charles reporting station has shown us slightly ahead of the historical average. I can only guess that given our cooler weather the predicted GDD for the next two weeks will be changing downward.

Modified Growing Degree Days (Base 50°F,March 1 through July 10)

You would expect t that as you move from north to south in the state, GDD would be accumulating at higher levels than northern Illinois. This matches up well with the typical planting dates throughout the state that gardeners use to begin their vegetable growing season.

If our weather pattern continues on the cooler side, those warm loving vegetables will be delayed in their development, which will delay any fruit set. The opposite has been seen on those vegetables and flowers that enjoy cooler temperatures; they are still growing very well.

This continues to be a "wait and see what happens" kind of summer.

About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.