somewhere underground, a sprawling organism trenches in, staving off efforts to come to the light. At least that’s the hope for superintendents, who don’t want a shallow root system to jeopardize their turf’s resistance to winter elements. To keep roots deep, researchers say, they can adhere to the following recommendations.
Increase mowing heights
The turfgrass principle of increasing mowing heights in the fall goes back decades, but is still important today, says Dr. Keith Karnok, professor of turf management in the University of Georgia’s Department of Crop and Soil Sciences. The higher the top growth is, the deeper the root system will be. “If you can mow it just a little bit higher, there’s more leaf material up there for the leaves to intercept the sun, to make the carbohydrates that will then go to the root system and be stored,” he says.
Bermudagrass fairways in the Transition Zone are susceptible to winterkill, says Dr. John Sorochan, distinguished professor of turfgrass science in the University of Tennessee’s Department of Plant Sciences. Superintendents can sustain significant root growth on those fairways by increasing mowing heights to around three-quarters of an inch or a little bit higher. “That helps, one, insulate the crown of the grass a little bit, but more so it encourages the taller the grass, the longer the roots, the more rooting, so for the winter storage of nutrients and carbohydrates to go into those growing points below ground,” he says.
Although golfers often express concerns about higher grass, it is worth it, Sorochan says. “The superintendent needs to do what he can do to protect the grass and have it come back the next year,” he adds.
Give the roots adequate nutrients
Root-feeding fertilization on putting greens can go a long way to maintaining root growth, says Dr. Douglas Karcher, professor in the University of Arkansas’ Department of Horticulture. Superintendents can apply either a spray or granular fertilizer. “Make sure that it’s not a nitrogen-only, that it includes all nutrients that might possibly be limiting growth, and so (superintendents) would need to have a soil test and have an idea of what needs to be applied,” he says. Potassium and iron can become deficient in sandy putting green rootzones, he says.
Generally, right before or after aeration would be the best time to fertilize, Karcher says. However, roots remain active late into the fall, longer than shoots. “Even when it’s gotten really cold in late fall and we’re not mowing much grass and we’re not getting a lot of clippings in the greens mower baskets, those roots are still growing almost up until the time when the soils are starting to freeze,” he says. “So that’s something that can be done later in the fall— a good complete fertilization using quick-release nitrogen sources.”
Don’t apply too much nitrogen
Fall fertilizer application rates vary depending on grass type, region and other factors, but superintendents should be careful with their nitrogen applications because too much nitrogen could slow root growth, Karnok says. “If you can hold back on your nitrogen some, your roots will be better off for it, which means you’re holding back the top growth from growing rapidly, so the carbohydrates are going to be stored in the plant or they’re going to root growth,” he says.
Many superintendents who lose turf in the summer aim to recover by applying heavy nitrogen heavily, Karnok says. “They say, ‘Well, I’ve lost so much grass, I’ve got to get this grass to spread back over, and the only way I’m going to do that, short of reestablishing, is get it to grow faster,’” he adds. If superintendents need to recover from summer losses, they can choose to apply extra nitrogen so long as they effectively maintain growth through other processes. If recovery isn’t a concern, they can save themselves trouble in the long run by applying less nitrogen.
Consider irrigating deeper and less frequently
Although it is common to apply light and frequent irrigation in the absence of rainfall throughout the summer, following aeration in the late summer or early fall superintendents should consider switching to a deeper, less frequent cycle, Karcher says. “Once roots are 5 or 6 inches deep, then you can water to that depth,” he says. “Then you can go every second or third day. By doing that, you will keep the surface a little drier between irrigations, and that will encourage even more root growth.”
Because conditions vary among courses, superintendents will need to determine for themselves how to best alter their irrigation cycles to fit fall conditions, Karcher says. “A lot of superintendents now have a TDR moisture probe, so if they’re monitoring their trouble spots on their greens—the spots that tend to dry out the quickest — they should know, ‘Ok, it’s not drying out as fast and we’re holding some moisture in here a little longer. Now we can maybe go an extra day between irrigation events,’” he says. By irrigating less frequently, superintendents will maintain the higher oxygen levels within the first few inches of the rootzone.
Use wetting agents to fight dry spots and desiccation
Often, sands in the rootzone of putting greens become coated with what Karcher describes as a “wax-like” organic substance, and those sands become hydrophobic over time. A common issue, dry spots can appear on any green that is prone to wetting and drying cycles.
Localized dry spots on greens are easy to detect in the summer because those greens are quickly drying out, Karcher says. Although dry spots aren’t as evident in the fall, they are still there. “I would encourage a superintendent to go ahead and treat with a wetting agent through the fall just to make sure that their entire rootzone is holding water because roots will not grow well anywhere that is deficient in water,” he says. “By just continuing with a good wetting agent program into the fall, they will maximize their fall root growth.”
Wetting agents can benefit superintendents through the winter. Preliminary data indicate early winter applications help reduce desiccation injury on ultradwarf Bermudagrass greens, Karcher says.