GDD – Why I’ve changed my mind

Last year I was talking a lot about using 6C as your base temp for timing your PrimoMaxxII programmes but now I think 0C is probably best. I shared this with the turf managers of the Nordics last week.

Growth Degree Days are a really simple model for measuring temperature based activities.

Generally there are 3 base temps used 0C, 6C and 10C.

How it works

Growth degree days are worked out by working out the days average temperature (Minimum temperature + Maximum temperature divided by 2)

That gives you an average temperature.

We then remove the base temperature from the daily average temperature which gives us the number of degrees above the base temperature. In this case you're left with 3 growth degree days. So really simply put a growth degree days is how many degrees Celsius has it been above a set figure.

Base Temperature

So choosing the best base temperature for what you are trying to measure is important to getting the best out of this model.

0C is best for measuring product degradation

Whilst growth grass growth may stop at 6C products such as Primo are still degrading, microbial activity and UV light are still actively breaking product down, the cooler it is the slower the degradation but it probably doesn't stop until temperatures reach 0C.

6C is best for measuring Cool season grass growth

Cool season grass growth roughly stops at 6C so this is a great figure to use to monitor and predict grass growth but not the best for measuring product longevity.

10C is best for measuring Warm season grass growth

Warm season grass growth stops at around 10C

Making it even easier

Changing from 6C to 0C is pretty easy to do on the Greencast website simply change the base temp figure and it does it for you.

If you're looking at Primo programmes for 2021 I'd steer you towards 200GDD at a base temp of 0C.

You won't see a big difference in the height of the summer when the average temperature is regularly above 6c but it will really help at the beginning and end of the season.

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