As lawns begin turning green in spring, the temptation is to add fertilizer to enhance the re-growth. LSU AgCenter horticulturist Dr. Tom Koske warns against giving in to this temptation.

"Putting fertilizer on too soon will feed and push pesky winter weeds," the horticulturist notes, adding, "If put on heavily, plant food will create a lush, soft growth of grass that will be sensitive to brown patch, leaf spot and other diseases. If we do get a late frost, these lawns will be hurt the most."

The horticulturist advises to let the grass awaken gradually and show definite activity. Mow new growth once or twice before fertilizing. Start with a complete fertilizer like 12-4-6, or you can choose 13-13-13 if you know your phosphorus is not too high.

If you have St. Augustine or Bermuda grasses, use 7 to 8 pounds per 1,000 square feet. Koske recommends a product with a slow-release action. On zoysia, centipede or carpet grasses, use 4 to 5 pounds per 1,000 square feet. Turf fertilizers with a high percentage of nitrogen and lower phosphorus and potassium are usually the best choice for feeding an average-fertility situation during the growing season.

After that application, use a nitrogen fertilizer or continue with a turf blend at a rate of one-half to 1 pound of nitrogen per 1,000 square feet each. The first number on the bag’s analysis is always the percent N (nitrogen) based on weight. On zoysia and centipede lawns, Koske recommends only one to two more applications this season using one-half pound of nitrogen per 1,000 square feet in a complete fertilizer turf blend.

Carpet grass needs no more fertilizer this year. For a spring nitrogen source, choose ammonium sulfate, over ammonium nitrate for a better response. The nitrate form will work better in summer, however.

If your LSU AgCenter soil test indicates a need for lime, apply lime in early to mid-spring or wait until mid-fall and cooler. Never apply more than 45 pounds of lime per 1,000 square feet directly over live grass. If more is needed, split the application at least several months apart.

Koske says to beware of a fertilizer that also has a weed killer in its formulation because some herbicides are meant only for use on Bermuda and zoysia lawns; read the label first.

Herbicides with 2-4D are best applied as liquid sprays – not as granulars. Keep such fertilizers/weed killers out of the flowerbed. Weed-and-feed products are often a good choice for spring lawn maintenance only if weeds are mildly present.

Broadleaf weeds often can be controlled using selective post-emergence herbicide formulations that contain two or more herbicides.

“Very useful formulations of herbicides are spray blends available for most southern grasses like those we grow,” Koske says, adding, “The time to treat weeds is while they are young and the weather is still cool. This will give the best control and the least damage to your turfgrass.”

A list of common consumer herbicides can be found in the LSU AgCenter's online publication 2940 “Louisiana Lawns Best Management Practices” or by contacting your local LSU AgCenter county agent.

If you wish to de-thatch or power rake this year, wait until late spring when the turf is actively growing for best recovery. Large dead areas are probably die-outs from winter kill or brown patch diseases. These often regenerate, but if they really look dead when the rest of the lawn is actively growing, they’re probably dead. Dead areas must be reestablished with new grass or seed before weeds take over.

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Editor: Mark Claesgens