2021 compared to 2020 just about the same for plant development

Every year people look at their plants and compare them to the weather and then compare them to the weather in years past. Then people usually say we are way behind last year or way ahead of last year.

In truth, we have never been way behind or ahead of the past years. We tend to be around the average plant development stages or phenology for this time of the year.

Phenology is the study of life cycle events of living organisms on earth; thus, plant phenology is the study of the life cycle of plants.

Another term that I often use in horticulture is growing degree days or GDD for short. GDDs are correlated with plant phenology and then used to predict insect emergence. And every year, they match up almost perfectly.

GDD are heat units that accumulate during the growing season and are calculated in a variety of ways. The easiest to understand is this: GDD=(daily high temperature plus daily low temperature) divided by 2, minus 50.

Therefore, a daily high of 55 F plus a daily low of 26 F on March 1, 2021 is 81; subtract 50 and you get 31 GDD. On March 2, a daily high of 42 plus a daily low of 29 is 71; subtract 50 and you get 21. So, at the end of March 2, 2021, we had a total of 52 GDD.

If you look at plant emergence that correlates with a GDD of 52, you find that speckled alder is at first bloom. Silver and red maples as well as Cornealiancherry dogwood are also just slightly past the first bloom stage.

GDD is used to help us with pest management. For instance, Eastern tent caterpillar (the ones that for the white nests in the crotch of trees, particularly those in the cherry family) eggs hatch at 92 GDD. This is around the time that Northern Lights Forsythia is in full bloom and the Cornealiancherry dogwood is in full bloom.

Therefore, if you were going to manage this caterpillar, you would look for these plants and when they are in full bloom, plant your pest management accordingly.

This is commonly used with gypsy moth emergence and the appropriate treatment. Gypsy moth caterpillars hatch just about the time when redbuds are in first bloom. Anyone who is planning on spraying the caterpillars can watch for this bloom to start.

With GDD, you just keep moving forward in the spring, but you never go backward. In other words, plants don’t start to bloom and then we have a few negative degree days, and they reverse the process.

I am sure with some of the spring weather we get that plants wish they could withdraw the blooms until it warms up! When the begin to leaf, the cat is out of the bag so to speak.

For more information on GDD and the phenology calendar, go to: go.osu.edu/GDDS. This link allows you to provide your zip code in order to see where your location is in terms of GDD.

And FYI, my zip code was at 30 GDD in 2020 on the exact same time as mentioned above, the end of March 2, 2020. Not really that far off from last year.