While suffering through the dog days of summer, we need to begin preparing our lawns for the winter.

Lawn winterizing products will soon be in local stores. Unfortunately, many products marketed as “winterizers” contain a high percentage of nitrogen fertilizer.

If nitrogen is applied in the fall, it should be done at least eight weeks before the average first frost date, which is typically the first week in November here in Northwest Florida. This allows time for the turfgrass to go dormant before cold weather can cause injury.

When applied too late, nitrogen fertilizer will promote shoot growth at a time when the grass metabolism is slowing. This results in a depletion of carbohydrates and stress on the plant. The new growth has a low cold tolerance and is often killed. Additionally, the nitrogen is available to the developing cool-season weeds and may increase the incidence of large patch disease.

The fertilizer analysis gives the percentage of available nitrogen (N), phosphorus (P), and potassium (K) in the product. Potassium plays the key role in winterizing because it has been shown to enhance cold tolerance of turfgrasses. If selecting a winterizer fertilizer containing nitrogen, be sure that the nitrogen content is low compared to the potassium.

Potassium is integral to many growth processes in plants, including: photosynthesis, starch and protein production, enzyme reactions, water movement, protein synthesis, cell wall components, and fruit development. Sandy soils tend to be more deficient in potassium, because it is leached easily. Soils with a low pH (acidic soils) may contain enough potassium, but it is not available to plants. Having a soil test performed is the best way to determine the need for potassium. Kits are available at the University of Florida Extension offices.

Besides applying potassium, there are cultural practices that help warm-season turfgrasses maintain optimum health through the winter.

•First, increase sunlight to the turf. As deciduous trees defoliate, keep the fallen leaves off the lawn. The turf that has been growing in shade has experienced reduced photosynthesis and, therefore, less carbohydrate production. Carbohydrates are needed for increased cold tolerance.

•Second, loosen compacted soils through spike aeration. However, core or plug aeration should not be done until after spring greenup.

•Finally, raise the mowing height in late summer. Not only will this promote deeper rooting, but will leave more leaf tissue for photosynthesizing and shading out weed seed.

Sheila Dunning is an agent at the University of Florida's Institute of Food and Agricultural Sciences Extension office in Crestview.