Calculating Growing Season


The last few days I’ve been investigating how to take advantage of free weather data from local weather stations. I was able to download some interesting data and graph it, which gave me a very accurate view of the growing season available here in my area.

First i downloaded Fahrenheit-based cooling data with a base temperature of 50F from (using temperature data from I was then able to generate a growing degree days chart from nearby weather stations. It looks like it is designed for heating and air conditioning, but it seems to work fine for gardening. I chose a base of 50F (10 C). I had to run the calculation as “cooling days”, since it is the temperature above 50F that I am interested in. I did a weekly chart for the 2010 growing season.


The precipitation graph i had to use data directly from Based on this data it appears that cool season crops could be planted as early as March if someone wanted to. I myself probably wouldn’t plant anything earlier than April 1st, and for everything else like Corn, they shouldn’t be planted earlier than May 8-10. I will plant my watermelon May 10-20 just to give them an extra week from the last frost. When both graphs are combined it seems pretty easy to guess which storms are likely to be late snowstorms. The last two snowstorm in 2010 appear to have been around April 30th and May 8-10th. Yep, sounds about right.

I’m still learning about GDD (Growing Degree Day’s) and how to calculate it properly, but from what i’ve learned.. Day’s to Maturity (often listed on seed packets) is often unreliable in Northern and colder climates. Depending on how warm conditions are, some plants will grow faster at higher temperatures. For those wishing to calculate GDD for their area i found this Growing Degree Calculator. In addition, Joseph from Utah has graciously graphed a few different locations for comparison.

Comparing 2010 growing season in different areas



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