First Cutting of the Greensward 2024

This event has become a regular feature as it (possibly) signals the arrival of a warmer climate. Previous reports can be found using these links for 2023 and 2022. It wasn't a great mow in terms of quantity though it was a welcome source of fresh green garden waste for the hot composting bins.

Photo 1: First Cut of our Neighbour's Lawn

There are a few data sampling issues when using the first grass cut of the year as a phenological indicator. Firstly, the decision to perform the first cut of the year is entirely within the realm of my neighbour. Second, I am fairly certain that aesthetics play a more important role than scientific rigour (e.g. making the first cut when the grass is 5 centimetres tall). Third, the date of the last mowing from the previous year may be a confounding factor (variable).

Nevertheless, that is not going to stop me looking for 'reasonable' correlations with weather data. I am discounting other factors (e.g. lawn treatments) and the presence of family pets (dog and cat); the former does not happen and I cannot quantify the latter.

So the first, and perhaps, most obvious factor to consider is the outdoor temperature. In Figure 1, I have plotted the average monthly temperatures (December, January & February) and the average Winter temperatures (DJF) for the past 5 years against the day of the year (Day 1 is January 1st) when the first lawn happened.

Figure 1: Effect of Average Monthly Temperatures on the First Lawn Mow of the Year

December, February and Winter temperatures behave as expected - that is, the warmer the weather the earlier the first cut of the greensward. January is a bit of an anomaly but the correlation is also the worst so we will not read too much into that without more data.

Interestingly, the best correlation by far is with the December average temperature. I recall from memory that grass stops growing at 4 ℃ though according to this article it is 5 ℃. We won't quibble over the odd degree. Soil temperature is probably more important than the air temperature - however, in the absence of severe frosts, air and soil temperature are probably interchangeable for our purposes.

Other factors that could influence the first use of the lawnmower might be (i) rainfall, (ii) sunshine, and (iii) severity and number of frosts.

Rainfall shows no overall correlation with the date of the first grass cut. Generally there is sufficient rain over the winter months - however, in 2023, February was very dry and the first mow was the latest in this time series.

Sunshine hours correlate rather well with the date of the earliest first cut (especially for January and February) but the overall effect is low (Figure 2).

Figure 2: Sunshine Hours vs Date of First Cut

Finally, I had a look at whether the number of frost days during the Winter season could be linked with the date of the first mowing. The data suggests that a higher number of frosts, especially in February, might delay the onset of the lawn mowing season but the relationship was not strong.

As might be expected, there is a temporal relationship between the first snowdrop, the first daffodill and the first grass cut - although the correlation between the first appearance of a daffodil and the first grass cut is much stronger.

Figure 3: Phenology Relationships

In summary, the warmer climate we are experiencing because of climate change can be readily seen in the earlier flowering of plants (snowdrops and daffodils) as well as an earlier start to the growing season after winter (grass).