The Master Gardener Articles

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Growing Degree Days

If you are interested in calculating when your apples or forsythia will bloom, you only need to know the following formula.

Add the high and low temperature for the day, divide by 2 and subtract 50. This will give you the growing degree day above 50˚ F. Biological response is minimal below 50˚ F, so we use the average temperature about 50˚ F. to get the growing degree days (GDD). For example, if today’s high was 80˚ F. and the low was 60˚ F, we would have (80˚ + 60˚ = 140 ÷ 2 = 70˚ - 50˚= 20 GDD) 20 GDD.

If these same temperatures happen again tomorrow, we would add 20 GDD + 20 GDD = 40 GDD. The GDD are added during the growing season to get a total GDD. These GDD have been correlated with plant response. You can calculate your own GDD or go on-line at http://www.oardc.ohio-state.edu/gdd and enter your ZIP Code and your GDD will be calculated.  A summary of phenological events (study of periodic natural phenomena in relation to climate) is given.

With this information, you will be able to predict when your various plants will bloom and when to spray for insect control.

For more information, go to http://www.oardc.ohio-state.edu/gdd or contact George McVey, Program Assistant, Horticulture, Master Gardener Coordinator at gmcvey@ag.osu.edu or all the Union County Extension Office at
937.644.8117 or toll free at (800) 589.8584.

The Master Gardener Offers horticulture advice and tips, focusing on current issues by volunteers who are with The Ohio State University Extension, Union County Master Gardener Program. For answers to gardening questions, call 937.644.8117 or e-mail gmcvey@ag.osu.edu. Hourse are 8 a.m. to 4:30 p.m. Monday through Friday