Extension@YourService: Centipedegrass Impacted by Cold Winter

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This spring I have received even more calls than usual from homeowners concerned about dieback in their centipedegrass. Centipedegrass is a warm season grass that is a commonly found in Sandhills lawns. It generally performs well here and is relatively low maintenance, compared to other warm season grasses such as bermudagrass, zoysiagrass, and St. Augustine grass. However, many warm season grasses were affected by our cold winter. According to the North Carolina State University website, TurfFiles (http://www.turffiles.ncsu.edu/), centipedegrass and the fine-textured zoysiagrasses (such as Emerald, Zeon) were hard hit by winter’s cold, while damage has been somewhat less in the coarse-textured zoysiagrasses (e.g. Empire, El Toro) and bermudagrass.

What I explain to clients is that turf which is weak going into winter is more susceptible to winter damage than healthy turf. While centipedegrass is low maintenance, it is not “no maintenance”. Many times I find that very little liming or fertilization has been part of regular lawn maintenance for many homeowners. While it is true that centipedegrass performs well at a lower soil pH (pH is a measure of soil acidity) than bermudagrass, our native soil pH can be as low as 4.5. Centipede performs best around a pH of 5.5 or 6.0, so some liming is needed. If soil pH is below or above the optimum range, plants are not able to take up fertilizer, even if it is applied. Another important aspect of our Sandhills soils is they are typically low in potassium, and centipedegrass has a high potassium requirement. Potassium, or potash as it is frequently called, is one of the big 3: Nitrogen, Phosphorus, and Potassium, or NPK (these correspond to the number on a fertilizer bag, and is the percent of that nutrient in the bag. For example, a bag of 5-5-15 is 5% N, 5% P, and 15% K, which is potash). So, it is very common that centipedegrass is potassium deficient, where lime is not properly applied and no high potassium fertilizer used (such as 5-5-15). One of the more important benefits of potash is that it helps plants withstand cold temperatures.

Another contributing factor that may lead to winter kill is the timing of fertilizer application. Centipedegrass should be fertilized using a nitrogen fertilizer just once per year, in the first week or two of June. Excess nitrogen fertilizer, using more than half a pound of nitrogen per thousand square feet, during the year and especially after July, can lead to excess growth which is susceptible to cold temperatures. Generally herbicide applications do not cause increased winter damage. However, another frequent homeowner practice is the use of a so-called “weed and feed”. This material is a two-in-one product, a pre-emergent herbicide combined with fertilizer. We’re all short on time, so it is tempting to use these products for efficiency. However, they are not recommended for centipedegrass, although you will often see the phrase “safe for centipedegrass” on the label. The problem stems from the fact that a pre-emergent should be used in the late winter/early spring, before warm season weeds begin to germinate. This is absolutely the wrong time to fertilize centipedegrass, and therefore this product is more of a detriment than a help to achieve a good lawn.

Finally, in addition to cultural practices which create weak turf susceptible to winter kill, microclimates can influence winter damage as well. Low areas that hold cold air, which flows like water downhill, shade, and compaction can all contribute to susceptibility.

There’s no quick fix for winter kill, or just having weak turfgrass. The answer is almost always the same: first, soil test (a free service by North Carolina Department of Agriculture), then follow the recommendations that are provided in your report, and finally adhere to the seasonal recommendations found in the Centipede Maintenance Calendar, available at the Cooperative Extension office or online at www.turffiles.ncsu.edu. For those with a smart phone, there is a very good NC State Lawn Care app for free download. This app provides alerts of pest and disease problems, lawn maintenance guidelines, and more. If you are disappointed in your lawn’s performance, the Cooperative Extension office has information to help get you on the right track.