Cold weather can damage or kill turfgrass on golf courses, as northern superintendents know well. Photos by Marc Szablewski
In the past, I have talked about the problems associated with extreme heat on golf course operations. On the other end of the temperature scale, extreme cold also causes its own set of issues.
In dealing with winter cold, Dale Bremer, Ph.D. — professor emeritus, Turfgrass Science, Horticulture and Natural Resources, Kansas State University — says, “The greens are the greatest concern, although fairways can be vulnerable too.” The dreaded winterkill is a problem for many superintendents in the north.
The different processes that can damage or kill turf are very much weather dependent. Desiccation occurs when exposed turf loses an excessive amount of moisture, which can lead to dehydration and winterkill. During cold outbreaks, the air is also extremely dry. The dangerous drying effect is magnified if the turf is exposed to wind. Direct low-temperature kill or crown hydration occurs when ice crystals form in hydrated crown cells, damaging or killing the cells. According to Bremer, “This happens when the crown cells aren’t fully dehydrated, i.e., the turf isn’t fully hardened for winter cold. The risk is greatest in the early winter following warm temperatures in the late fall or in an unusually warm early spring. This can also happen anytime during the winter if extremely low temperatures exceed a turfgrass’ cold-hardiness.”;
Anoxia occurs when the turf becomes covered with ice (ice encasement) for an extended period, reducing gas exchange with the outer atmosphere. A reduction in oxygen and a buildup of toxic gasses can kill the turf. Bremer says, “This can happen during rapid declines in temperature in the fall, before the turfgrass has hardened, but mostly occurs when turfgrass has been de-hardened in spring after going through freeze/thaw cycles.”
Proper species is key
In dealing with winter cold, Bremer says, “The proper species of turf is the best place to start.” Brad Jakubowski — assistant teaching professor, Plant and Irrigation Science, Penn State University — notes, “Many warm-season (C4) grasses are more susceptible to cold temperatures.”
Bremer explains, “Bermudagrass is widely used for greens across the south and has been pushing farther north in the transition zone, due largely to its greater tolerance to heat stress at low mowing heights. But bermudagrass is more vulnerable to low temperatures than creeping bentgrass, which is more widely used across the northern U.S.”
Snow cover can actually help turfgrass underneath it by serving as an insulator.
Marc Szablewski, Class A superintendent at St. Andrews Golf Course in Overland Park, Kan., and 18-year GCSAA member, says, “Our zoysia is most susceptible to extremely cold weather. Winterkill has been a big problem over the last couple of years.”
Jeff Heaton, Class A superintendent at Lake Geneva Country Club in Lake Geneva, Wis., and 13-year GCSAA member, says, “I have primarily bent greens, and they seem to handle cold weather well. I think bent is OK under ice as well, for up to 90 days even. Poa (annua) seems to struggle during extreme cold. I would be nervous if it was under ice for more than 30 days. The bent seems to overtake the Poa in cold winters and springs, or at least it doesn’t get worse. This winter and spring were mild, and the Poa has gotten considerably worse.”
Amos Stephens, general manager/Class A superintendent at Settlers Bay Golf Club in Wasilla, Alaska, and 26-year GCSAA member, says, “Bentgrass is the best for cold hardiness without a close second. When I first arrived here 25 years ago, the facility was growing Poa triv(ialis). Once I took over as superintendent, then partner, it’s been bentgrass ever since.” One consideration Stephens adds of the conversion starting with the 2005 season to a blend of A4, G7 and Crystal Blue Links bentgrass greens: “The supply of bentgrass is the dictator on which one I am able to grow. We can only grow what the farmers are willing to supply us with in seed.”
But even for bentgrass, the threshold temperature for cold damage may vary. Bremer says, “I haven’t seen research to confirm that, but it is very likely at higher latitudes where it is colder, creeping bentgrass will become more acclimated, or hardened, which will lower the temperature threshold at which damage occurs compared to lower latitudes that experience higher temperatures overall. Thus, the primary reason for differences in cold tolerance in creeping bentgrass at different latitudes is likely due to acclimation. But other factors could also lower the temperature threshold for freeze damage, such as cultural practices that maximize the health of the creeping bentgrass (proper fertilization, cultivation, etc.). Lastly, it is possible there may be differences in cold tolerance among creeping bentgrass cultivars, but there’s not much research to confirm that.”
Marc Szablewski, superintendent at St. Andrews Golf Course in Overland Park, Kan., says he puts out covers only on areas that have had past issues with cold weather.
Snow as an insulator
Nature sometimes helps out superintendents. “As long as the turfgrass has acclimated to the cold and the soil under the snow remains frozen, then snow can protect the turf from extreme low temperature kill,” Bremer says. However, he warns, “With prolonged or repeated freezing and thawing of the soil (usually in the spring), it is possible for the turf to become de-acclimated and, thus, more vulnerable to winterkill, even under snow. Also, freezing and thawing may form an ice cover under the snow, which over time may cause other issues for the turf, such as anoxia (low oxygen), toxic carbon dioxide levels, etc. Annual bluegrass, which is used in greens in some parts of the north, is more susceptible to this than creeping bentgrass.”
Szablewski notes, “We had golf until Christmas this past year, then a 7-inch snowstorm followed by a week of sub-freezing weather. The heavy snow helped a lot by insulating the grass and protecting it from the extreme cold and wind damage. Most winterkill is a result of exposed turf to those extreme conditions along with drier conditions.”
Heaton adds that his bentgrass greens typically weather cold weather well, he says, “but we typically have snow cover when it gets extreme.”
Since snow cover may not be adequate for protection, Jakubowski says, “Using growth covers will also help protect the grasses.” But as Bremer notes, “They are expensive to implement, and temperature thresholds at which they should be deployed are not well understood.”
As for the superintendents, their approach varies with their location.
Heaton in Wisconsin says, “I do not cover my greens. I just don’t feel my bent greens need to be covered. I might if I was all Poa.”
Szablewski in Kansas says, “If we put covers out, we will just place them in areas we’ve had issues with in the past.”
Stephens in Alaska, where winter temperatures often drop below 0 degrees and have hit minus-30 degrees, “Yes, we do cover the greens. We have a very elaborate system to manage 180 days of snow and ice. The order of our covering system is: permeable grow cover first, that is last to come off in the spring to allow for heat and stimulated spring green-up; resin-coated polymer similar to EnkaMat that holds up the snow layer and allows for forced air flow and gas exchange; plastic vent tubing; impermeable cover to keep the snow, rain and ice out. Takes us two days to deploy to all 21 greens and then another three days to secure with sandbags for the winter. We blow air once a week or as temps allow through the winter.”
Although the use of covers can help protect turf, they’re expensive, and the temperature at which they should be deployed is far-from-settled science.
Bring on the sand
Topdressing with sand has long been a standard practice for winterizing greens.
“I feel it is important to have as much sand as possible on the greens before they stop growing,” Heaton says. “Sand left from aerification, then several topdressings after that.”
Jakubowski explains: “Heavy topdressing can help protect the crowns.”
Bremer adds, “Topdressing, done in tandem with verticutting/power raking, is used to control the buildup of thatch, which is a layer of plant material on the surface. As the thatch layer becomes thicker, the turfgrass crowns can become elevated (i.e., they are no longer in and protected by the soil but are in the thatch layer). This exposes and makes them more vulnerable to direct low-temperature kill as well as increased desiccation.”
An additional concern according to Bremer are “low-temperature diseases, such as snow mold,” and Heaton concurs, noting he finds pink and grey snow molds to be among the most damaging turf diseases.
Although all turfgrass species are susceptible to this disease caused by a fungus infection, creeping bentgrass is more prone to injury. Snow mold is more prevalent when a thick snow cover persists well into late winter. The disease spreads under the snow cover, affecting leaves and stems. Heaton adds, “We have to spray for snow mold, with multiple products and modes of action.”
Szablewski takes other measures to protect his greens. “I think preventative sprays can help prevent turf from injury and harden up the plant, particularly bentgrass,” he says. “A good wetting agent, a preventative fungicide app and plant nutrients help winterize the plant. Having proper moisture in the plant and subsurface when the ground freezes is the best way to prevent winter injury and desiccation.”
How low can it go?
To get an idea how cold it can get at your location, check with the National Centers for Environmental Information (www.ncdc.noaa.gov). NCEI will have all of the past weather records for sites close to you. This information may also be available locally by state climatologists at www.stateclimate.org. or by local agricultural Extension offices.
Another source of information is the USDA Plant Hardiness Zone Map (https://planthardiness.ars.usda.gov). The PHZM is based upon the “average annual extreme minimum temperature” at a given location calculated over the climatic standard of 30 years, in this case 1991 to 2020. It should be emphasized that this is the average of the coldest winter temperatures over this time; the plant hardiness zones “do not reflect the coldest it has ever been or ever will be at a specific location.”
Jeff Heaton pauses for a cold-weather selfie during an October irrigation blow-out in Wisconsin. Photo by Jeff Heaton
The Federal Emergency Management Agency has a National Risk Index for a variety of natural hazards (https://hazards.fema.gov/nri). Included are the possibilities of a cold wave, which is defined as “a rapid fall in temperature within 24 hours and extreme low temperatures for an extended period. The temperatures classified as a cold wave are dependent on the location and defined by the local National Weather Service (NWS) weather forecast office.”
Consistently cold, “normal” winters are less problematic. Superintendents know what to expect and can prepare for them. But abnormally warm winters can still have cold spells, and as noted above, these can do more harm. The worst of the unusually cold spells are known as “arctic outbreaks,” when temperatures can far exceed low temperatures that typically occur in winter, sometimes dropping to record-low levels.
Interestingly, such cold outbreaks can often be predicted well in advance. The NWS produces 6-to-10-day and 8-to-14-day outlooks (https://www.cpc.ncep.noaa.gov/products/OUTLOOKS_index.php) that have shown great accuracy in forecasting below-normal temperatures well ahead of their occurrence. As we get closer to the event, forecasts become even more accurate in terms of timing and specific locations that will be affected and by how much.
This coming winter, the NWS has changed the format of its cold-weather fore-cast products. Rather than just highlighting wind chill, the new products will incorporate cold temperature information to stress the concerns of cold temperatures even without wind. There will be Cold Weather Advisories for less-extreme events and Extreme Cold Weather Watches and Warnings for the worst events. The actual criteria varies by region in relation to average or normal winter temperatures. These cold weather products can be issued a day in advance. In Canada, Environment Canada also issues Extreme Cold Warnings, and those criteria again vary with location.
Ed Brotak, Ph.D., was a longtime professor of atmospheric sciences at the University of North Carolina, Asheville.