Many people fertilize their lawn too late with too much nitrogen. They wrongly call this practice “winterizing.”
The word “winterizer” is misleading. Many of the so-called winterizer fertilizers available in our area can cause more damage than good. The time to fertilize our warm-season grasses in Florida is during the growing season, not when the grasses are going to “sleep” for the winter.
The grasses we use to create lawns are warm-season grasses. They include centipedegrass, St. Augustinegrass, bahiagrass, Bermudagrass, zoysiagrass, carpetgrass, and seashore paspalum. Centipede, St. Augustine and zoysia are the most common lawn grasses in our area.
These grasses actively grow during the warmer months of spring, summer and early fall. They are designed to go dormant in fall and winter. The cooler temperatures (particularly cooler night temperatures) and shorter days of autumn trigger these grasses to slowdown.
Applying high nitrogen fertilizer when your lawn is trying to go dormant for the winter is somewhat comparable to you drinking a pot of regular coffee before going to bed. Nitrogen interferes with the dormancy process, forcing the lawn to “wakeup” (produce new tender growth) at the wrong time of year. You set the lawn up for cold injury.
That young tender growth is more susceptible to cold injury and is likely to be damaged by the first frost or freeze. And many times this damage goes unnoticed until the following spring when sections of the lawn fail to green up. In North Florida, mid-September would be the latest that the University of Florida recommends applying nitrogen to our warm-season lawns.
If you insist on “winterizing” your lawn, use a fertilizer with low nitrogen (the first number in the fertilizer analysis) and high potassium (the last number in the analysis). In most cases, the center number (phosphorus) should also be low. Examples of such fertilizers include 9-2-24, 5-2-14, 8-2-34, 5-0-22, etc. Remember, more potassium than nitrogen. But never use a high nitrogen fertilizer late in the season such as 27-3-3 or some similar fertilizer with high nitrogen and low potassium, even if it is labeled as “winterizer” fertilizer.
Also, for the fertilizer to benefit your lawn, it needs to be applied while the grass is actively growing, when the grass can readily take it in. After the lawn is dormant and when the soil temperature is cooler, much of the fertilizer that could have benefited the grass is wasted and may end up in our groundwater.
For research based information on maintaining a Florida lawn, contact your local UF/IFAS County Extension Office or log onto http://hort.ifas.ufl.edu/yourfloridalawn
Larry Williams, UF/IFAS Extension Agent, Okaloosa County, September 28, 2016