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Growing Degree Days (GDD) - January 2024 Summary - Amy Stone Erik Draper


The Plant Phenology and Growing Degree Day (GDD) posts and impacts have been a Buckeye Yard and Garden onLine (BYGL) staple for years. GDD will continue to be an important part of the blog written to assist green industry professionals, Extension professionals, Extension volunteers, and people with a passion for plants and pests too.


While there isn't usually a lot to report as part of the January summary, members of the OSU Buckeye Environmental Horticulture Team (BEHT) have been discussing the relatively mild weather in November, December and early January – at least previous to this recent taste of winter with plunging temperatures and strong winds – and wondering if there would be any impact on the GDD calendar in 2024. 


The purpose of the first GDD post would normally show that no matter where in Ohio you are from north to south, or east to west, we all begin at zero on January 1st, but it that really the case this year? Will the days late in the 2023 where we experience some days where temperatures topped above 50F have an impact on plant and insect development in 2024?  


As you will notice in the chart below, some locations have picked up some units in the first month of the year, where others have not. 


We know that as temperatures warm, we will begin accumulating growing degree day (GDD) units - and that is indeed we are seeing so far in February with our recent warm weather - even a recording breaking day time high temperature last week in some areas of the state.


Readers will continue to see those updates in the BYGL on a monthly basis, but there is no better way to track GDD and ultimately the plant blooms and insect activity on your own. Be sure to save this website ( ) as a favorite, and set those calendar reminders now to check the website regularly.  


BYGLers will be monitoring the online calendar closely, and then compare that with what we are seeing outdoors with plant and pest development. Only time will tell if what we see online will match what we are seeing in real-time early this season as a result of what we experienced late in 2023. We will also be looking for your observations across the buckeye state as well.  


Here is a Growing Degree Day Refresher if GDD is new, or you need a little review!


GDD are a measurement of the growth and development of plants and insects during the growing season. Development does not occur at this time unless the temperature is above a minimum threshold value (base temperature). The base temperature varies for different organisms. It is determined through research and experimentation. The actual temperature experienced by an organism is influenced by several factors. These factors affect growth and development. For instance, depending on the weather, an organism's temperature may be a few degrees more or less than that recorded. An organism may spend its time in the shade or under direct sunlight. The fertility and nutrient content of the soil directly affect the growth rate of plants and thereby indirectly influence insect growth rates. The presence of weeds and precipitation may indirectly influence development. Due to these factors and some other scientific considerations, a base temperature of 50 degrees Fahrenheit is considered acceptable for all plants and insects. (Source: OSU Plant Phenology Website)


The one thing that we do know is that the sequence of events – both plant and pest development – consistently occurs in the same order no matter the weather.  


At the end of each month this calendar year, there will be a GDD Summary Alert Posted to BYGL. While today's post has some areas seeing zeros - it is the start of the calendar year – we will have to see if that is true. As you can see below, 20 Ohio locations (City, County, and Zip Code) have been chosen across the state and will continue to be used for the monthly updates. 


GGD Chart, ending January 31, 2024


Ohio City (County)

Zip Code  

GDD Unit Accumulation 

Bryan (Williams)



Toledo (Lucas)



Sandusky (Erie)



Elyria (Lorain)



Burton (Geauga)



Jefferson (Ashtabula)



Van Wert (Van Wert)



Findlay (Hancock)



Medina (Medina)



Mt. Gilead (Morrow)



Mt. Vernon (Knox)



Steubenville (Jefferson)



Dayton (Montgomery)



Springfield (Clark)



Columbus (Franklin)



Lancaster (Fairfield)



Marietta (Washington)



Cincinnati (Hamilton)



Hillsboro (Highland) 



Ironton (Lawrence)




Not seeing your city or zip code? No worries! You can always check out the website, type in your Ohio zip code, and ground truth what you are seeing with what the calendar says should be occurring. 


Once Mother Nature decides to turn up the heat, additional information including observations will be posted on BYGL so stay tuned to GDD Updates.


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