Turfgrass management in the Carolinas can be quite challenging. During the growing season, many homeowners will have to manage turf through periods of excessive rainfall followed by periods of drought. Insect and disease problems can crop up at a moment’s notice. Along with these problems, some may also have to work with poor soils. With all the potential problems during the growing season for the lawn, winter is the one time of the year people tend to neglect it. For more information see, HGIC 1221, Winterizing Lawns.
South Carolina lies within the transition zone with respect to turfgrass adaptability. This transition zone is a region between the warm, semi-tropical and tropical areas of the south and the cooler, temperate climates of the north. Managing turf in this area can be a challenge as it lies on the northern regions of warm-season turf adaptability and the southern regions for cool-season turf adaptability. Growing seasons with above normal temperatures, or hotter, can stress the cool-season turfgrasses. Winters with below normal temperatures and extended freezing conditions can be stressful on the warm-season turfgrasses.
Most of the lawns in South Carolina are planted with warm-season turfgrasses. These include bermudagrass, zoysiagrass, St. Augustinegrass and centipedegrass. Cool-season turfgrass plantings are predominately limited to the upstate and the foothills regions, mainly planted with tall fescue.
Winter turf loss is primarily a problem on the warm-season turfgrasses in the Carolinas and is generally referred to as ‘winterkill’. Winterkill is a somewhat ambiguous term that is used to diagnose turf loss during the winter. This is usually seen in the spring when the turf fails to green back up. It is best to avoid using the general term winterkill when diagnosing a winter turf loss as this does not provide a specific cause. To avoid winterkill in the future, it is important to determine a specific cause so problems can be fixed.
Winter turf loss on warm-season turfgrasses can be caused by numerous conditions or through a combination of various climatic anomalies. Direct exposure to low temperatures and winter desiccation are two primary factors that are involved in winter turf loss. Direct low temperature kill can be defined as simply turf loss when air temperatures drop so low that the turf plant is killed. This will usually occur as the temperatures fall below 25 F and can be more pronounced when temperatures stay at this level for several days.
Winter desiccation is the loss of turf during dry winters when little rainfall occurs and supplemental irrigation is not provided. Air temperatures are not involved with winter desiccation as turf loss can be seen during mild winters if rainfall is lacking. Therefore, it is important to monitor rainfall during the winter, even if the turf is dormant, and irrigate the turf if rainfall has not fallen for a month to six weeks.
There are cultural practices that can be implemented to reduce or possibly prevent winter turf loss. The most important turf management practice is to be sure the turf is as healthy as possible before the first frost. A healthy turf, void of insects and diseases, can better withstand the cold temperatures of winter. A deep, healthy root system is better able to withstand short periods of drought.
Adequate soil drainage is important as areas that tend to stay wet will see more winter turf loss than those areas that are well-drained, especially during wet winters. Nitrogen fertilization after mid-August should be avoided as this will promote new growth. However, late season additions of potassium can increase winter hardiness especially on sandy soils. Raising the mowing height ½ to 1 inch over the normal summer mowing height in September and October will allow the plant more leaf surface to produce winter food. Removing thick thatch layers next spring in warm-season lawns will keep the growing points of the turf close to the soil surface which will help protect the buds from freezing temperatures. For more information on managing thatch, see HGIC 2360, Controlling Thatch in Lawns.
Even with our best turfgrass cultural practices in use and hardening our lawns off properly, winter turf loss can occur. When it does, it is important to determine why the turf died and correct any problems before replacing any dead turf.