A smooth and uniform putting surface with a medium to fast ball-roll speed is the goal of many superintendents and green committees alike. That begs the question: “What is medium-fast?”
Well, that’s a good question. Ultimately, speed depends on the resistance forces that turfgrass blades in a putting green apply to a rolling golf ball, which is why higher-cut greens are typically slower in pace.
However, many other factors affect ball-roll speed after the cutting height is set. These reasons include the expectations of decision-makers, the skill level of the course’s members and frequent players, and the capacity to provide the desired ball-roll speed within the season of play.
Faster putting greens often result in weaker turf and a slower pace of play, so it’s important to help decision-makers realize the challenges that come with speed. While many factors are important to consider, no other activity influences turf physiology and performance more than mowing.
Established standards and unintended consequences
Luxury automakers often tout themselves as “the industry standard.” For many years, the established standard for mowing height on putting greens was 1/8 (0.125) inch. On average, this would produce a medium Stimpmeter speed of 7.5 to 8.5 feet.
In recent years, many golfers have asked for faster speeds and longer rolls, causing superintendents to adjust their management practices to meet the demand. Regardless of whether the demand for faster speeds came from televised PGA events or clubhouse chatter, accommodating the request generally begins with a lower height of cut, which usually results in greater stress on the turf.
When turf is mowed with the appropriate frequency, it results in shoots that have a greater life span, and stand density generally increases as cutting height decreases, too, within reason. But as the height of cut is decreased, roots recede, lateral stems do not grow as aggressively and leaves become more succulent.
Together, these effects mean that lower mowing can provide a putting surface that is smoother, denser and faster compared to higher heights of cut, but the overall capacity of photosynthesis declines, as do tolerances to abiotic and biotic stresses and the turf’s ability to recover.
Cultural management becomes even more important to prevent decline, as do herbicide and fungicide programs that prevent turf loss and weed invasion. Because putting greens cut to lower heights are more likely to decline during stressful summer months, the likelihood of voids and weed invasion increase, and both of those factors negatively affect ball roll.
Read more: Using Greens Rollers to Manage Turf
Golf course superintendents typically mow putting greens daily, perhaps skipping one day each week during stressful periods. It may also be advisable to use solid rollers rather than grooved ones during stressful periods, especially for the clean-up cut on the perimeter of a putting green that commonly suffers mechanical injury from frequent mowing.
Solid rollers are less aggressive than grooved rollers. They don’t sink into the putting green surface to the same degree as grooved rollers, and they also raise the effective height of cut without adjusting the bench setting, which is another recommendation for alleviating stress.
Rolling is a practice often used to increase the pace of putting surfaces for special events or tournament play. However, to reduce the stresses of mowing even further, many superintendents are omitting multiple days of mowing each week in exchange for rolling without sacrificing pace or surface smoothness. Alternatively, some superintendents get similar results by increasing the height of cut to reduce stress, and roll approximately two days each week to maintain ball roll speed.
Improving ball roll and stress tolerance is not always as simple as increasing or decreasing the height of cut. Many newer, creeping bentgrass cultivars with exceptional turfgrass density, such as A- and G-series cultivars, almost need to be mowed to a cutting height of 1/8 (0.125) inch or less, which was once considered “ultra-low.”
Today, heights of cut commonly range from 1/10 (0.1) inch at facilities with more resources (and probably newer, very dense cultivars), all the way up to 5/32 (0.156) inch at facilities with potentially fewer resources and/or older cultivars. Golfers tend to prefer the pace and smoothness of closer-cut turf, but such low heights of cut are only advisable if turf density is maintainable. If turf density declines, pace and surface smoothness will decrease regardless of the height of cut.
The good news is that we can rely on other cultural practices to increase the pace of putting greens in lieu of adopting ultra-low mowing heights and the stressed putting greens that they produce.
Topdressing and irrigation
Sand topdressing is vitally important for diluting thatch and maintaining firm greens that are resistant to surface disruption. Firm greens are smoother, faster and less likely to be damaged by mowing, even ultra-low mowing, as a result.
Putting greens with excessive thatch development are more often scalped by mowing and retain surface moisture that is problematic to turf health and the pace of ball roll. Light, frequent applications of sand topdressing (0.5 to 1.5 ft3/1,000ft2 every seven to 14 days) are preferred.
Research shows that sand topdressing, by itself, can be sufficient to dilute thatch development, but your preferred method of cultivation may aid the incorporation of sand. The goal should be to apply sand frequently enough to match the growth rate of turf to limit the formation of layers in the profile. With appropriate thatch dilution, it’s much easier to provide firm and fast conditions through irrigation management – in other words, light watering on a daily basis, with supplemental hand-watering only in drier locales.
Nitrogen and plant growth regulators
Nitrogen fertilizer management greatly affects how consistent the pace of putting surfaces is because of the relationship between N and shoot growth, and superintendents have reduced annual N over the years in favor of “lean and mean” conditions. Spoon-feeding programs are used to provide only what is needed by plants to recover from damage, and annual N has been reduced from 3 to 4 pounds per thousand square feet to less than 2 pounds per thousand square feet in some cases.
At the most basic level, plant growth regulators (PGRs) reduce overall shoot growth, meaning less clipping production and an improved quality of cut, which improves ball roll. These useful products reduce vertical growth as well as scalping, and when used appropriately, they have been shown to increase shoot density and even rooting under heat and drought stresses.
If PGRs are applied at too high of a rate – or even too frequently at a low rate – turf may become over-regulated, leading to poor quality and a reduced capacity to recover from wear stress or disease injury.
The bottom line
There are several options for managing the speed of putting greens without altering the height of cut. Considering the reduction in overall stress tolerance that often results from ultra-low mowing, it may be wise to explore an integrated approach for managing the pace of putting surfaces, rather than relying solely on the height of cut.
In addition, we should take care to ensure that the pace of putting surfaces is appropriate to their design. It’s important to consider that regular play is less affected by increasing pace on flatter greens, but significantly undulating putting greens can become virtually unplayable at the pace that results from ultra-low heights of cut.