Winterizer lawn fertilizers are heavily promoted and are in stores now. People often ask if they should use them.

“The truth is, most winterizers sold are not really designed for southern turfgrass species such as St. Augustine grass or centipede grass but are perfect for Kentucky bluegrass or other northern ‘Yankee’-type grasses,” says LSU AgCenter turfgrass specialist Ron Strahan.

The problem is their high nitrogen content.

“I did a recent survey of the lawn winterizers available in the Baton Rouge area,” Strahan says. “I was surprised to see approximately 90 percent had an analysis of 10 percent to 32 percent nitrogen. These so-called winterizers probably would be a better fit as a late-summer application rather than in fall or winter.”

The catch, Strahan says, is that nitrogen applied in the fall stimulates growth just when southern grasses become dormant or semidormant heading into winter.

“Nitrogen fertilizer applied in fall or on dormant to semidormant St. Augustine, centipede and zoysia lawns can lead to increased brown patch incidences and winter kill,” Strahan says.

On the other hand, potassium — the third number on a bag of fertilizer — can be beneficial to the lawn this time of year because this nutrient increases winter hardiness and helps lawns fight diseases.

“Last year we had a good bit of winter kill from our unusually harsh winter,” Strahan says. “In fact, I investigated several lawns and collected and analyzed soils samples. Often, potassium levels were low and contributed to the inability of the lawn to withstand two ice storms and temperatures in the teens.”

Potassium works like antifreeze inside plant cells, preventing them from freezing and rupturing.

Low-nitrogen or no-nitrogen fertilizers, such as 0-0-60, would work great for winterizing your lawn. But the lawn may not need any potassium at all.

“You won’t know for sure unless you get a soil analysis,” Strahan says. This is an excellent time to collect soil samples and submit them to the LSU AgCenter soils lab for testing. Soil sample reports provide a wealth of information concerning the pH and overall fertility of your soil along with potassium, the real winterizer nutrient.

You can find soil test forms and more information online at lsuagcenter.com/soiltest or at an AgCenter office. Many area garden centers and nurseries have boxes that contain the necessary forms. The cost for each test is $10.

Got a gardening question? Write to GardenNews@agcenter.lsu.edu