GDD are a measurement of the growth and development of plants and insects during the growing season. This development does not occur unless the temperature is above a minimum threshold value, or a base temperature. The base temperature varies for different organisms and is determined through research and experimentation. The actual temperature experienced by an organism is influenced by several factors. These factors will ultimately affect the growth and development.
Here are some examples:
*If you take a walk outside, you will notice there are areas in your own landscape that are warmer than others. Exposure to the sun, or lack of sun, wind, or protection from the wind, can create a microclimate that could accelerate plant and insect development, or reversely, slow that process of development down. Simply put, a plant in full sun will likely begin flowering sooner than that same plant in a location that is shaded. Proximity to buildings and driveways can also be factors.
*Fertility and nutrient content of the soil can have a direct affect on the growth rate of plants. While we want healthy plants, too much of a good thing is not good. There has been some research that has shown that plants that are overly fertilized and pushing a lot of vegetative growth can have an increase of pest pressure in some cases.
*There are other factors that can also have an impact on plant and insect development including the presence of weeds or unwanted plants in a given area, or too much or too little water either through irrigation, hand watering or mother-nature.
Because of these factors and the variability within even a landscape and some other scientific considerations, a base temperature of 50 degrees Fahrenheit is considered acceptable for all plants and insects. If you are curious about the base temperature and math behind how GDDs are calculated, check out this webpage on the OSU Growing Degree Days site at: https://u.osu.edu/ohiophenologycalendar/glossary/
Here is where you can dig in and how this site can helpful at the local level. All you need is an Ohio zip code. What I find fascinating is that whether you might be a little head of the curve, right on, or a little lagging, the sequence of events is the calendar remains the same.
The calendar is a chronological list of plants – first bloom and full-bloom; and insect activity. So how does this work?
*Click on this website: https://www.oardc.ohio-state.edu/gdd/
*The date will default to today’s date. Type in your Ohio zip code. *Click on “Show me the Calendar” rectangle. *You will be shown a snapshot of what is happening in your zip code with the GDD accumulation and upcoming phenological events. *You will have a lot of information at your fingertips. It is important to do some ground truthing to make sure the information that is on the website matches what you are seeing locally.
I am hopeful that everyone will click-on the website and find out what their GDD is and begin to learn more about the world around them.