DATE: 02/22/06

CONTACT: Clemson Extension Home & Garden Information Center, 1-888-656-9988

WRITERS: Joey Williamson, and Chuck Burgess

WINTERIZING LAWNS – IS IT REALLY NECESSARY?

CLEMSON - Every fall, many homeowners ask, “Do I really need to help the warm-season lawns prepare themselves for winter?” The presence of pallets stacked high with winterizing products in stores by late August would seem to imply that the answer is yes. This article answers questions that should help clarify this subject.

1. Are winterizing products appropriate for all types of turf?

Both cool and warm season turfgrasses grow in South Carolina and most of these products do not differentiate between the two grass types. Fescue is a cool season grass and grows best in cool temperatures. In the fall, you should begin fertilizing fescue with lawn fertilizer according to soil test results. In South Carolina, the term winterizing applies only to warm-season grasses such as centipedegrass, St. Augustinegrass, Bermudagrass, and zoysiagrass.

2. Should a product high in nitrogen be applied to warm-season turf in the fall?

It is alright to lightly apply nitrogen in the late summer and fall as long as the application is at least 4 weeks before the first average frost date. For centipede lawns, extend this time frame to 8 weeks (Table 1). A light application means ½ pound of actual nitrogen per 1000 square feet of lawn. To determine how much of a product contains ½ pound of nitrogen, divide the first number in the analysis (in 5-5-25, for example) into 50. The result (=10) is the number of pounds of the product that contains ½ pound of nitrogen.

When selecting a winterizer fertilizer containing nitrogen, be sure that the nitrogen content is low, compared to the potassium. This will allow you to apply appropriate amounts of potassium without applying excessive amounts of nitrogen.

When applied too late and too heavily to warm season turfgrass, nitrogen fertilizer will promote shoot growth at the same time the plant’s metabolism is slowing. This results in a depletion of carbohydrates and stress on the plant. The new, tender shoots are also less tolerant of cold temperatures. Furthermore, the additional nitrogen will be available to cool season weeds, and will increase the incidence of large patch disease, which is very prevalent in the fall.

3. Should other nutrients be applied to the lawn in the fall?

Potassium has been shown to enhance cold tolerance of turfgrasses. If a soil test indicates that your soil is low in potassium, it can be applied at a rate of 1 pound of potash per 1000 square feet of lawn. Materials available include fertilizers low in nitrogen such as a 5-5-25 (use 4 lbs per 1000 square feet) or muriate of potash (0-0-60; use 1.6 pounds per 1000 square feet), or potassium sulfate (0-0-50; use 2 pounds per 1000 square feet). However, if your lawn has been fertilized throughout the summer with fertilizers containing potassium, it’s unlikely a fall application would be helpful.

An excessively high rate of potassium fertilizer may lead to foliar burn, or may cause a competitive inhibition of other nutrient uptake. Excessive potassium is especially known to affect magnesium uptake, which will result in a lighter green turf color. Always apply granular fertilizers onto dry foliage to reduce the likelihood of salt burn.

4. Are there other ways to help a warm season lawn prepare for winter?

One way is to increase sunlight to the turf. Turf in shaded areas stays cold longer and produces fewer carbohydrates due to reduced photosynthesis. Carbohydrates are needed for increased cold tolerance. Another way is to loosen compacted soils through aeration or a gypsum application. Compacted soils are colder than well drained areas.

Keep fallen leaves off the lawn, as this will reduce the turf’s ability to photosynthesize for carbohydrate production. And lastly, raising the mowing height in late summer will not only promote deep rooting, but will leave more leaf tissue which will produce more carbohydrates. An increased height will additionally reduce weed seed germination in the fall before the turf goes dormant.

In summary, a lawn that has been well maintained through the summer is prepared for winter. If you are concerned, follow the recommendations above and submit a soil sample to your local extension office. Among other helpful information, the report will include the potassium level of your soil.

For more information on lawn care and for answers to your other gardening, pest and food safety questions, visit the Clemson Extension Home & Garden Information Center website at http://hgic.clemson.edu or call us toll-free at 1-888-656-9988.

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