Special K

When it comes to plant health, potassium doesn’t get as much attention as other elements, such as nitrogen. However, potassium (K) is a key ingredient in any protocol for maintaining healthy turf, especially golf courses maintaining full or partial Poa annua putting surfaces, and at proper levels, it may even ward off the effects of winterkill.

Potassium affects, among other things, the photosynthesis process, moisture retention and a plant’s ability to deal with stress. And it might best be described as a nutritional supplement for the plant.

Mark Kuhns, a 40-year turf industry veteran, can attest to potassium’s impact on mitigating heat- and cold-stress issues in turf.

As the director of grounds at the historic Baltusrol Golf Club in Springfield, N.J., not far from New York City, where he recently completed his 16th season, Kuhns’ 36 holes encompass a vast 500 acres of turf, including eight acres of putting surfaces that are a blend of 75 to 80 percent bentgrass and 20 to 25 percent Poa annua. Situated on the northeastern edge of the Transition Zone, Kuhns and his team, which includes course superintendents Dan Kilpatrick (Lower Course) and Jim Delaney (Upper Course), deal with stress during the peak of the season – including during the 2016 PGA Championship – and cold-stress issues in the winter. The staff utilizes potassium throughout the property.

“We’re spoon feeding almost everything in the summer months,” Kuhns says. “Of course, when we do aerification, we put a lot of phosphorous down, but we always include potassium with that in some amounts. Most of the soluble fertilizer we put down contains potassium.”

The Baltusrol staff utilizes a fertilizer that contains 4 percent potassium. Kuhns and his team developed the product in-house in the early 2000s. It can be purchased and stored in bulk, a circumstance that has benefited the club’s bottom line in the years since. As cold weather approaches and fall aerification commences, the potassium level is increased.

“When you’re doing your aerification, if you want to up your potassium level say in the fall a little bit to strengthen things up, you might go with something in a 1:1 ratio of nitrogen to potassium, or even 1:2,” Kuhns says.

Potassium’s benefits have been well-documented within the turf industry, Kuhns adds. “Everybody does it for different reasons,” he says. “Certainly, the plant cells are stronger with potassium (in terms of) photosynthesis, respiration, absorption of water. All these things are improved with a certain amount of potassium. The thickness of the cell walls, resistance to heat stress, stress factors in the summer, drought, heat, cold. Everybody puts it down at different rates.”

In fact, Rutgers turf researcher Dr. James Murphy remarked in a March 16, 2015 online dispatch of Plant & Pest Advisory (“Winterkill on Annual Bluegrass: Don’t Skip the K”) that a huge difference could be seen between nopotassium and potassium-fertilized Poa annua plots. Two weeks after the Poa test plots lost their winter ice cover, the no-potassium plots steadily lost their green color and become blotchy victims of winterkill. In contrast, green, healthier looking turf was observed in plots that had received potassium fertilization.

“Take home for me – don’t let your Poa annua turf become potassium deficient,” Murphy notes. “(Graduate student, Chas Schmid’s) data for suppressing anthracnose severity indicates that a soil test (Mehlich 3) =50 ppm K and a tissue level of =2% K in the clippings are indicators that the K level is good.”

From metabolism photosynthesis, to the capture of sunlight and conversion into chemical energy as sugars, and then their reutilization of those sugars, potassium impacts practically everything, says Dr. Larry Murphy, a consultant for Compass Minerals, which produces plant nutrients. With an extensive agriculture background, Larry Murphy has seen the effects of potassium firsthand.

We’re spoon feeding almost everything in the summer months. Of course, when we do aerification, we put a lot of phosphorous down, but we always include potassium with that in some amounts. Most of the solvable fertilizer we put down contains potassium.” — Mark Kuhns, Baltusrol Golf Club

Larry Murphy also cites potassium’s effectiveness as a preventative measure against moisture stress. “Potassium is involved in regulating the opening and closing of the stomata on the leaf surface through which gas exchanges and through which water is lost,” he says. “If there is an inadequate supply of potassium and moisture is limited, then even more water is lost and the plant loses its ability to withstand that kind of stress.”

Application rates and intervals vary widely, depending on climate, geography, and blend of turf. Larry Murphy advocates what might be described as a three-pronged approach. “One (application) needs to be made early in the season when everything is starting to kick off and really get going,” he says. “One needs to be made in early summer, and a third in the fall to winterize that plant against winterkill. That’s only three, but if the superintendent is making applications every time, they made a nitrogen application ... it would be good for the plant.”

Potassium aids in the task of hardening the plant for winter. “In those colder months, that’s going to give it one additional protection against freeze damage,” Larry Murphy says. The actual application rate varies considerably based on elevation and latitude. Even a minor variance can be impactful.

During the winter months, Todd Raisch defends his 27 Poa annua greens at Ridgewood Country Club in Paramus, N.J., against problems such as crown hydration, desiccation, direct temperature kill, and, of course, snow and ice cover. His task is complicated by the fact that the winter climate in northern New Jersey features significant temperature fluctuations, particularly early in the season. Three days of temperatures near or below freezing could be followed a few days later by temperatures of 50 degrees or higher; or the other way around. The extreme variance in temperature makes the task of hardening the plant in preparation for winter more challenging.

Raisch, who has served as Ridgewood’s superintendent for the last 21 years, says if his club were located perhaps an hour’s drive or so farther north, the task of preventing direct temperature kill would in some ways be simplified because the cold weather generally remains in that region once it arrives.

Raisch considers potassium an important tool in his agronomic arsenal. He and his team normally apply 2.5 pounds of potassium per application in a ratio of 1:2, nitrogen to potassium, or perhaps 1:3 in some circumstances. “I think potassium is part of any good Poa strategy,” he says.

Raisch does have one fact in his favor: his greens are closed each winter. However, not every superintendent has that luxury.

For example, nearby Paramus Golf Course, a public facility that hosts roughly 50,000 rounds each year (compared to 30,000 at Ridgewood), has Poa greens that date back to 1927, although they have been renovated to improve drainage.

Andy Schuckers, the club’s superintendent and general manager, has never considered converting to bentgrass greens simply because they would never stand up to the club’s volume of play. But Schuckers still faces the issues that arise when a Mid-Atlantic golf course operates year-round. Maintaining his Poa surfaces in a sometimes-harsh climate requires a preventative approach, one that wards off potential problems before they become major headaches.

“We deep tine five or six times a year,” he says, “and do venting or needle tining throughout the year.” During spring and fall aeration, Schuckers utilizes three-quarter-inch tines that penetrate about eight inches into the soil. Periodically, perhaps four times during the season, he uses quarter-inch tines. “That’s done as a preventative measure,” he says.

The same for venting or needle tining, which is done periodically through the season when conditions warrant.

Schuckers also utilizes an organic fertilizer that contains approximately 4 percent potassium. As cold weather sets in, he will increase his potassium ratio if he determines it’s necessary, based on the results of soil samples.

None of these measures offer a 100-percent guarantee against problems. All a superintendent can do is try to tip the odds in his favor. “You can only work with Mother Nature,” Schuckers says. “You can’t beat her.”

Rick Woelfel is a Philadelphia-based writer and frequent GCI contributor.