COVER STORY
M EAS U RIN G
PUTTING GREEN FIRMNESS By Daniel O’Brien; Doug Karcher, Ph.D. and Mike Richardson, Ph.D. This article was originally published in GCM, June 2021.
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utting green firmness can be a difficult metric to define and interpret. Turf scientists discuss different measurement methods and how to translate the data into management decisions.
We’ve been extremely fortunate to work with a lot of neat “gadgets and gizmos” during our research, taking all types of measurements, usually on putting greens. We’ve collected a lot of interesting data and learned quite a bit along the way, but we must confess that when it comes to firmness, we still have a lot of questions. We’ll work our way back to those, but let’s start with the basics of what we do know.
Putting green firmness: Important and elusive In and of itself, firmness isn’t a difficult concept to understand or appreciate. After all, it’s one half of the celebrated mantra of “firm and fast,” it has direct implications on playability, and the overwhelming consensus is that it’s a desirable attribute of a quality golf course. We care about firmness because it relates to ball-bounce and shot-hold capacity and the durability of the putting surface. When managed properly, firmness can be a defining hallmark of the skill and strategy required to play the game at the highest level. But where the waters become a little murky is when you try to articulate what ideal firmness looks like. We often talk about firmness not so much by what it is, but by its absence — “These greens are too soft/too hard.” Ultimately, firmness is about
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rewarding (and demanding) quality golf shots while preserving the integrity of the putting surface. The key point in all of this is, with firmness, sometimes it’s easier to attach a number than a definition. With technology today, we can measure a lot of things, but firmness measurements on their own are just a number. If you’re going to spend the time collecting those numbers, you need to have a picture of what that number looks like at the moment of impact when the golf ball meets the putting surface.
Tools for measuring putting green firmness When it comes to producing a number you can work with, there are several options for how to do it. We’re going to separate those options into two basic camps: accelerometer measurements and depth measurements (Figures 1 and 2). There is a third “indirect”option for assessing firmness through volumetric water content(VWC), which we’ll touch on as well. Starting with accelerometer measurements, the Clegg Impact Soil Tester is the standard in turfgrass research. Originally developed by Baden Clegg, Ph.D., for testing road subgrades (1), this device has proven particularly useful for evaluating the hardness(or softness) of turfgrass surfaces. The accelerometer
