Basic climatic data - a must for the modern turf manager

No two starts to the calendar year are the same nowadays, with significant variability in temperature and rainfall. That’s why recording basic climatic data (rainfall, maximum and minimum air temperature) is a must.

Using this temperature data inputted into a growth model such as Growth-Degree-Days (GDD) allows us to make comparisons year-on-year.

Comparisons that can help us understand where our turf is and, above all, provide data for communication to management and members alike.

Below is the GDD formula I use to make growth comparisons:

Growth Degree Calculation

(Max daily air temp + Min daily air temp) / 2 – base temperature (6°C base temp) = GDD

Note - I use 6°C as my bRugase temperature because that’s when we see active grass growth, American models use 0°C. GDD has no units of measurement, it is simply a scale to quantify the potential of the grass plant to grow vs. air temperature.Crick

In the table below, we compare 2025 with 2024 so far, using rainfall and GDD (6°C base temp) data from a location in Oxfordshire.

So, using this basic data we can already see some big differences year-on-year, we are approximately 50% drier y.t.d and had a particularly dry month in March. Not great if you have overseeded unirrigated areas and need germination, such can be the case when converting winter season pitches to cricket outfields as an example.

Looking next at the GDD totals to the end of March, we had only received 27% of the 2024 figure, quantifying what we already knew and felt, that the start of 2025 has been a cold one. Mother Nature hasn’t been in an obliging mood this year temperature-wise, so if you have surfaces that were heavily scarred from Microdochium last autumn, you may still be waiting for tillering and recovery.

Now, April has been a warm month with temperatures touching 20°C in places, ideal for grass growth. Or has it?

Let’s take a day in early April as an example, using data from the same location above and plug it into the GDD model.

April 8th, 2025                

Max temperature = 15.5°C         Min temperature = -0.4°C          

Inputting those numbers into the GDD formulae gives us;
(15.5+-0.4)/2 – 6 (base temp) = 1.55 GDD

Now, I work on 4 – 6 GDD as indicative of good growth, so in this case, although we have warm day time temperatures, the effects of cold nights and grass frosts result in a GDD figure that is indicative of a very low growth rate.

Again, an invaluable aid in communication to show why the current weather isn’t completely ideal for greenkeepers and groundsmen/women alike, even though I think we would all take a dry start to the year over a wet one!

visit: www.weatherstations.co.uk
Send your questions for Mark to: editor@pitchcare.com