Winter especially in the northern part of the country, can be a welcome down time where the day-to-day stress of maintaining adequate turfgrass cover for sporting events is reduced. But, weather conditions during winter can put stress on the turf. Fortunately, careful attention to management practices can help to reduce or eliminate this damage.
Most athletic fields will be in the same condition — or worse off — in the spring compared to what they were at the end of fall. Most of our maintenance practices aimed at improving field conditions, such as topdressing, aerifying or overseeding, don’t benefit the turf as much when conducted in winter. This is due to the poor growing conditions that are encountered either in winter, or even into early spring. But practices that are scheduled for late fall, or even around fall sports schedules, are important to ensure that next season’s fields will be in good condition.
Damage during winter
For the most part, the cool-season turfgrasses are more capable of withstanding low temperatures than the warm-season grasses. But the grasses that we manage as athletic turf vary in their tolerance to cold temperatures.
Kentucky bluegrass is the most cold tolerant of the species and rarely is any lost due to low temperatures in winter. Tall fescue and perennial ryegrass, on the other hand, are not as tolerant of extreme cold and some loss can occur in the northern parts of the country. While there are differences among cultivars, we generally start to see winterkill on these two species when temperatures reach minus-20 to minus-25 degrees. This is important to consider because if, for example, you live in a cold part of the country and were considering overseeding with ryegrass, you may wish to ensure that the cultivars you’re using are tolerant of the typical temperatures observed in your region.
Damage to turfgrass during winter can also occur due to desiccation, where drying winds cause water loss from the leaf faster than it can be replaced. Or, in warmer parts of the region where cool-season grasses are grown, we do see periods in winter where there’s turfgrass growth but soil conditions are excessively dry. Our cool-season grasses are adapted to survive these conditions. But in situations where the turf is mowed short or if it’s being grown on a sandy medium (like a typical athletic field), it might be a good idea to intervene.
Though it may seem counterintuitive, we do see occasionally the need to irrigate turf in the winter to prevent damage or loss from desiccation or excessive drying. While you should winterize your irrigation system in December, it may be better to irrigate as needed at some point during the winter months and then rewinterize the irrigation system.
When turfgrass is under ice and snow for an extended period, we can also see an increase in tissue loss. This is typically observed only in the northern states and doesn’t occur every year. What’s more common is to see damage occur on fields that are used during freezing conditions, or when frost is present. In these instances, traffic causes cellular damage that result in browning of the leaf blades that’s sometimes visible until the following spring. Therefore, care should be taken to avoid the use of fields during frost/freezing conditions. In addition, mowing should be delayed until after the frost dissipated and the leaf blades have dried.
Overseeding is important because grass that germinates in the fall has a stronger root system the following spring. The optimal time to seed in fall is between Aug. 15 and Sept. 15. But research conducted by Frank Rossi at Cornell University and Dave Minner at Iowa State University has shown that frequent applications (weekly or every other week) of high rates of seed throughout fall can significantly improve cover on heavily trafficked areas. The idea is that some of the seedlings will germinate. While many of them may be damaged or killed by foot traffic, some will persist. In addition, a “seed bank” allows for some of the seed to remain dormant and germinate at a later time. The soil heaves and forms cracks due to the temperature fluctuations, and some of the seed will fall into these, which will increase germination when temperatures warm.
Read More: Winter Maintenance Work in the South
A lot of dormant seed and germinated seedlings may succumb to diseases or desiccation during winter. But this approach has been shown to be quite successful, even more so with rapidly germinating species such as perennial ryegrass and tall fescue. It also works with Kentucky bluegrass — much of the bluegrass seed might not germinate until spring, which greatly increases the chance the seedlings will be killed by spring traffic. But the surviving seedlings will be able to spread via rhizome during the spring.
Mowing is typically not done during winter. When the grass begins to grow enough to justify mowing in late winter is usually when you’ll want to resume your fertility program. During the fall, cool-season turfgrass in heavily trafficked areas should receive up to 1 pound of nitrogen per 1,000 square feet per month. Ideally, the nitrogen applied at this time will be quickly available. A late fall nitrogen application has been shown to be the most important for growth of cool-season turfgrass. This should be timed so that the grass is green but no longer growing. Also, a quickly available source of nitrogen should be used. Late fall nitrogen applications have the potential to contaminate surface water, so you shouldn’t apply if the soil is frozen. (Soil tests should ensure that potassium and phosphorus levels are adequate.)
On cool-season turfgrass, the benefits of late fall applications of phosphorus related to improved winter hardiness are unclear. Generally, you should only apply phosphorus at establishment or based on soil test results. One of the functions of potassium in the plant, however, is to improve winter tolerance. Therefore, there’s a benefit to applying potassium with nitrogen during the late fall application.
Aeration and topdressing are normally done during times ideal for the growth of grass. But there are advantages to aerating the most heavily trafficked areas of the field after the last event in the fall and should be conducted on areas where traffic will restrict recovery of the turfgrass. Topdressing can then be applied to help level the surface and even provide some insulation to the turfgrass crowns against winter conditions. What to topdress with is dependent on the physical properties of the soil under the field. In general, you want to match the particle sizes as closely as possible. Sand can be applied even to a clay soil and over many years will gradually bring about improvements in drainage.
Another option for native-soil fields is the use of compost. Applied at a depth of 0.25 to 0.5 inches, especially in conjunction with core aerification, compost produces an early spring green-up effect similar to an application of fertilizer.
Covers that are breathable are used frequently both to extend greening in the fall and also to promote early spring green-up. The effect can be substantial, with dormancy delayed by four to six weeks in the fall and spring green-up being pushed one to two months earlier compared to uncovered turf.
The covers do a variety of things in addition to just warming the turf and soil. They can protect the turf against damage caused by frosts or freezes. They can also deter traffic on the field, which reduces wear and tear on seedlings. In general, you’ll want to keep the height of the turfgrass at 1 inch or less under the covers in order to avoid the grass blades laying over, which can promote conditions for diseases such as snow mold.
Weeds can occasionally be an issue as well, especially the winter annuals, such as common chickweed or annual bluegrass. The best strategy to reduce encroachment by these weeds is to ensure adequate turfgrass coverage. If herbicide applications are necessary, check the label carefully, as most herbicides negatively impact seedling turfgrass.
Read More: Controlling Snow Molds on Turfgrass