## Sunday, May 26, 2013

### Are We Behind? Compared To Years Past, Yes.

I've mentioned growing degree days once before for timing certain chemical applications. I thought I would revisit this quickly because I have been asked a lot lately about generally how far behind we are on growing, summer conditions, etc... The answer depends on what you are comparing things to I suppose. Usually, for good or bad, we compare things to the previous year or prior few years. So I updated the GDD chart to include the last 5 years plus 2013 to give you an idea of how many growing degree units we have accumulated thus far in relation to the past five years.
A quick note on how we calculate growing degree days: GDD are calculated by taking the average of the daily maximum and minimum temperatures compared to a base temperature, Tbase, (I use 32° F).

$GDD = \frac{T_\mathrm{max}+T_\mathrm{min}}{2}-T_\mathrm{base}.$

From the chart it is pretty obvious we are behind the last 5 years, and when looked at the atypical weather of 2012 we are behind about 1,000 GDD. I think you have to go back to 1975 to find a colder month of April then what we just had. In the end it's hard to put a definitive answer on the 'behind' question, but there is no question that everything is happening later in the year so far in 2013 than what we are accustomed to.