Looking at the clipping volume growth ratio

A question came up about optimum clipping volume and whether that quantity of clippings changes by season. That amount must change for any location at which there are seasonal changes in the weather. That is, for almost everywhere in the world, the expected amount of clippings is going to change through the year.

Jason Haines came up with a logical and effective way to standardize this. He’s called it the “turfgrass speedo” and the “growth ratio.” I wrote about this on page 7 of the Turfgrass Genki Level report.

Jason has suggested that adjusting N and PGR applications through the season to keep this ratio close to 1 has been a great way to keep healthy grass and good playability. He can also favor bentgrass over Poa annua by keeping that ratio a bit below 1, and favor Poa annua over bentgrass by keeping the ratio above 1.

I took a look at this for the warm-season korai greens at Keya GC in 2021.

In the spring as the grass is coming out of dormancy, the ratio is way above one.1

Then from June through to the end of October, the ratio (as a seven day moving average) is always less than 3.

It seems that a value of 1 works pretty well for korai greens too, and for tournament play, a ratio less than 0.5 would work well.


  1. This is because there is some clipping volume from mowing but the temperatures are so cold that the GP is close to zero. Seeing this type of discrepancy between growth and GP as grass goes in and out of dormancy provides some insight on how the GP model might be adjusted. ↩︎

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