The Science of Green Speed (Part 1)

Green speed or ball roll has been measured on putting greens since before the invention of the “Stimp Meter.” In 1935 Edward S. Stimpson developed the first device to quantify the speed of greens, but it was not regularly used by the United States Golf Association (USGA) until 1976. In 40 years, putting green speeds have dramatically increased from two main factors: better mowers and light weight rollers.

In 1970, the US Open putting green height was about 5.5mm. The most recent mowers allow superintendents to mow grass below 2.0mm in height.

The reason behind this is number of blades on a reel. Greens mowers have increased from 11 blades to 15 blades in the last five years. According to Texas AM University “The specific clip of a reel mower is dependent upon the number of blades and the rotational speed of the reel” and “a reel with a certain number of blades, can only vary with the rotational speed of the reel in relation to ground speed. With the same number of blades, the faster reel speed will produce the shorter clip length.”

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In other words, as the mower runs across the green to cut the grass, we increase the speed that the reels spin and the clip length is reduced, where there are less peaks and valleys in the cut—resulting in balls rolling smoother and faster. Below is a depiction of a poor quality of cut magnified 10x which shows the peaks and valleys that can occur when the clip rate does not match the speed of the mower.

Once the speed of the mower and the clip rate are matched the quality of cut greatly improves and the surface is far more uniform.

The development of lightweight rollers has revolutionized the smoothness of putting greens. Rolling on a regular basis is only possible on sand based putting greens, as continuous rolling compacts all other soil types. This more recent development in green smoothness also increases speed of greens. New research from Michigan State and Dr. Tom Nikolai (The Doctor of Speed) indicate that rolling also decrease the expression of disease causing fungi, or at least reduces the amount of disease present on putting greens. This too serves to improve ball roll.

Between cutting and rolling, putting greens have never been shorter or smoother, but these are only two aspects that deal with the surface of the green, all the hard work is done below surface in the soil/sand, which is the foundation for the science of green speed. Next issue, look for cultural practices that allow the use of mowers and rollers on a regular basis.