GvX clippings

Questions have been arriving regularly about the turf GvX. I’ll answer a couple of them here.

Days with no mowing, and zeros

I’ve received a few variations of this question.¹ It goes something like this.

How should I handle days without a mow, or an area that doesn’t have data recorded for that day?

On a day with no mowing, there is no clipping volume. On a day with no mowing, the clipping volume is also blank—it is not a day with a mow and 0 clippings, it is a day with no mowing and there are 0 clippings. The table of simulated data below may help to clarify this.

This table is showing temperature, GP, clipping volume in mL/m² from greens 3, 5, and 11, the daily average clipping volume, the trailing 7 day average clipping volume, and the trailing 7 day GP, shifted ahead by a day so we are calculating GvX in real time with the temperatures that the grass was growing in.

Now what about this zero thing? Look at June 6, for example. G3 has missing data, G5 has a clipping volume of 14, and G11 has missing data. It’s not that they were zero. It’s that the data are missing. We have a daily average of 14. Not a daily average of (0 + 14 + 0)/3 = 4.7. We should not calculate as if those are zeros. They are not zeros. Those are missing data.

Take a look now at June 10, and June 15. On those days we did not mow. The daily clipping volume is properly going to be zero on those days. But we don’t want to fill in all those cells with zeros on days we don’t mow. We leave those blank, as missing data. I then create a fakeVol variable that is automatically 0 on days when mowing was not conducted.

Those are two slightly different ways of handling missing data (or zero values) in the clipping volume data, and these need to be handled in this way in order to get the correct GvX. See also the PACE Turf GvX page for example spreadsheets.

What should my GvX be?

One of the reasons for the GvX is to answer the question “what should my clipping volume be?” I’m now getting the question “What should my GvX be?”

First, this is for you to decide. How much do you want the grass to grow? The GvX is a way to put a number to how much the grass is growing. The rate that it should grow is up to you.

Second, if you insist on a number, I think in-season GvX values in the range from 10 to 300 are reasonable. If the GvX is less than 10 or more than 300, I’d be surprised. A lot of people are getting good results on putting greens with a GvX in the 20 to 100 range. But this depends on grass species and a lot of things. I just saw a professional tournament on greens with a GvX at 150. The GvX that you should have is whatever your GvX needs to be.

Third, I thought I’d try to explain it like the height of NBA basketball players. How tall do you need to be to be one of the best NBA players? Michael Jordan was 198 cm. Steph Curry is 188. Victor Wembanyama is 221 cm. There’s no fixed height. You can be a great player at 188, at 198, at 221.