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. The website uses weather stations across Ohio to determine what the accumulations, and provides visitors their GDD and where they are in a biological calendar of certain plant blooms and insect activity.