Nature Notes: Greenhouse showed signs of spring awakening

Nine years ago, noted in my field notebook Feb. 11, 2007, I wrote a simple entry: Fred Struck from the Traverse des Sioux Garden Center in St. Peter, Minn., reported that once again plants in his greenhouse had begun to come out of dormancy and start growing.

Struck added that from this special date onward, close to his latitude, each year on sunny days it will be hot and humid in greenhouses.

Struck is a horticultural science graduate of the University of Minnesota and a sharp observer, and he has convinced himself and others that the awakening in greenhouses on or close to Feb. 11 each year can be attributed to the sun's higher position in the sky.

When he first shared this observation with me 10 years ago, I thought I would like to experience it firsthand. I brought my Gustavus Adolphus College students to his greenhouse. There, they got a sense of how the season was changing and winter was moving slowly into spring. Yes, this awakening in greenhouses is truly a spring sign, and the Gusties and I experienced it in Fred's greenhouse over several years.

The interiors of our cars and trucks now warm up even when parked in the sunlight on cold days. We also see snow melting on dark surfaces when the air temperature is below 20 degrees. These things happen because the sun has moved higher in the sky, concentrating its rays.

Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. He is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.