Ron Wilson

Ron Wilson

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What is your GDD? (Growing Degree Date)

So what is your GDD -or growing degree day? Before you reach for a piece a paper, a pencil, and a calculator to figure out what your number is, check out the OSU's Growing Degree Day website. This website does the 'math' or the calculations to determine your GDD for you. All you need is an Ohio zipcode - type it in and hit enter. The website uses weather stations across Ohio to determine what the accumulations, and provides website visitors their GDD and where they are in a biological calendar of certain plants in flower and insect activity. 

It is important to note that microclimates in our own landscape, or landscapes that you manage, can sometimes be ahead of, or even maybe lagging behind, but this information can be so useful and interesting. It is important to note that even if you appear to be ahead or behind of what the website is indicating, the order of plant bloom and insect activity remains the same. The sequence of order remains constant. 

This morning, when I checked the website, Toledo (zipcode - 43615) was at 205 GDD. What this means is that gypsy moth caterpillars have begun to hatch (192 GDD), Donald Wyman crabapple is in first bloom (197 GDD), snowdrift crabapple is in first bloom (198 GDD), full bloom of compact garland spirea (205 GDD), full bloom of Koreanspice viburnum (GDD 205), and on the horizon is the egg hatch of the azalea lace bug (206 GDD).

Click below for calendar

This is why GDD is so useful! 

Additionally, it fun (at least I think so) to compare where we are today, compared to the past. Sometimes we think, this spring is so early, or it feels like we are far behind an average spring. This website can help us remember what was happening horticulturally on this same day in the past. And even more cool, you can change the date too! So let's compare this spring, April 15, to year's past on the same day, April 15. 

  • 2021-205 GDD
  • 2020-90 GDD
  • 2019-85 GDD
  • 2018-83 GDD
  • 2017-201 GDD
  • 2016-129 GDD
  • 2015-78 GDD
  • 2014-80 GDD
  • 2013-69 GDD
  • 2012-275 GDD
  • 2011-66 GDD
  • 2010-206 GDD
  • 2009-103 GD

So if you look and compare we have definately accumulated more GDD than other years, except for 2012 when at this same time, we had accumulated 275 GDD. 

Hopefully you have been using the website and tracking your GDD, and then heading outside to verify what the website says we are at, to what your plants are doing. It really has been spot on this season. I can look out from my office window and see many of the plants that are included on the website. Additionally, I can head out to the field and monitor for and observe insect activity that is included in this list. 

The post would not be complete without thanking Dan Herms, Denise Ellsworth, Ashley Kulhanek and others who have worked on this project including the research and data collection that allows OSU to have such an excellent website that used by many. 

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