GDD Calculators and Maps

I’ve seen people sharing Growing Degree Day (GDD) calculators in various topics here and thought it would be helpful to compile them all in one place. Some give more detail than others, but they are all useful. If you don’t know, GDD is an approximation of how much heat your plants receive in the growing season. With some caveats, all else being equal, more heat = more growth or fruit ripening. Knowing your average GDD can be helpful for determining if a fruit or nut will grow well for you.

If anyone else knows of a good one I missed, feel free to add it. Also please chime in with a more thorough discussion of GDD.

Note: All the resources I know of focus on the contiguous US. I’d really love if anyone could point me to similar resources for other regions of the world.

Northeast GDD calculator: Climate Smart Farming CSF Growing Degree Day Calculator

Midwest: U2U@MRCC: Corn Growing Degree Days (GDD) (thanks @Travis)

Southeast: Growing Degree Days Calculator – AgroClimate

Growing Degree Unit (GDU) Calculator | Pioneer Seeds

Cooling degree days (same idea from another direction, intended for estimating AC energy use): (thanks @Barkslip)
I’ve seen reference to minimum cooling degree days for pecans, so I included this one as well.

If you’d like to quickly compare between regions, here is a web map of average annual base 50 GDD (30 year) that I made using data from the National Phenology Network. I wasn’t able to make it as detailed as I would like due to limitations of the free version of ArcGIS Online. I divided the country into 500 GDD sections, but I was only able to get 10 categories for color, so it is colored in 1000 GDD increments. You can search for your address and click on the map to see the minimum GDD for that zone. If you’re close to the line of the next zone up, you can presume you’re closer to the high end of your zone.

Another good source (but slightly harder to use) is the National Phenology Network data visualization tool. It takes some getting used to, but you can access information such as first bloom times for common species, GDD, and more. I personally like the gridded layers.

Here’s the formula/rules to calculate your own GDD if you have the data:


In the NE and upper Midwest the NEWA weather stations are helpful–they have disease prediction models for certain diseases/pests. NEWA - Station Pages


With a good backyard weather station (and Linux) you can calculate your own GDD.

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Nice resource! A backyard weather station is high on my list of things I want. If I get one, I’ll probably end up doing a Python script to calculate my GDD since I’m not currently running any Linux boxes. Alternatively, any spreadsheet software should be able to handle it as well.

weeWX is Python. There have been reported successes porting it to Windows although the developers aren’t currently behind such efforts.

Any spreadsheet software should be able to handle it as well.

The calculations are within what a spreadsheet should handle, but they are a little arcane.

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Neat. Theoretically, it should be straightforward to just use it on other platforms. As for DIY scripting or spreadsheet calcs, I’m thinking of just the simplest sense of GDD as a rule-of-thumb measure as detailed in the NDAWN link I added above. You’re right that the more sophisticated calcs you link to would be more of a project.

Whew! Started to go down the rabbit hole of the source code and “how hard could it be?”. A fun project, but need to get back on track! And it looks like there’s a Windows fork on GitHub, anyway… has the most comprehensive set of GDD data and formulas I’ve seen anywhere.

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Ah, good one. I had found their mapmaker and was going to use that as the source data for my map, but it had trouble exporting a raster for the whole country. Definitely more of a power user experience.

Yes, I agree it is a rather poor UI experience. But the data is there and you can play around with thresholds and formulas for many days of amusement. (as I did)

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