LSU AgCenter Horticulturist Says Beware Of Wrong Lawn Winterizers

Thomas J. Koske, Claesgens, Mark A.  |  4/19/2005 10:29:12 PM

News Release Distributed 09/21/04

Louisianians, especially in the northern part of the state, are beginning to "winterize" their lawns. Before they do so, however, LSU AgCenter horticulturist Dr. Tom Koske says it’s important to make sure you’re using the right product.

That means looking carefully at the product bag to make sure it’s intended for the grasses we grow in this area.

"Many lawn winterizing products sold locally are really made for cool-season grasses that grow in the northern states," Koske says, explaining, "Winterizing cool-season grass is opposite of winterizing our warm-season grasses."

The horticulturist said he recently noticed a local retailer selling three different kinds of winterizing products - all formulated for northern grasses. Cool-season winterizers have a fertilizer analysis with high nitrogen (N) – first number on the product bag – and lower phosphorus (P) and potassium (K) – the second and third numbers listed.

"These products are wrong for our permanent grasses, Koske says, adding, "We want to strengthen our lawns for winter, not weaken them."

Winterizing southern lawns means to slow down grass growth and increase potassium (K) - that third number on the label. This process toughens plant tissues for the winter freezes ahead.

Research has shown that higher levels of plant potassium enhance tolerance to a broad range of environmental stresses including cold damage. Therefore, a good strategy is to maintain high levels of soil potassium throughout the growing season and especially in the fall, Koske advises.

"With high potassium available all season, special winterizing would be unnecessary, and the turf would be in best shape to handle environmental and pest problems all season long," Koske says.

Phosphorus, the middle number on a fertilizer bag, generally is not critical unless you know your soil is deficient in this nutrient. Extra phosphorus in the fall would just promote winter annual weed germination, Koske explains.

"If in doubt, just use muriate of potash (0-0-60) or do nothing," the LSU AgCenter horticulturist advises.

For those with a less than an ideal lawn fertility program, Koske offers some end-of-season tips:

–Reduce nitrogen fertilizing to at least one-third of the normal application or less. If you have not gotten a lawn by September, you should not try to continue to grow it out in fall. Reducing nitrogen fertility slows growth and allows the grass to toughen. It also reduces fall’s brown patch disease.

–Finish the growing season with a fertilizer high in potassium. If applying only potash (potassim) to avoid extra fall nitrogen, use 1-2 pounds per 1,000 square feet of muriate of potash (0-0-60). Apply to a dry lawn and water in to avoid any salt burn. In most cases this is all you need.

–Keep up adequate moisture in the fall. We often want to forget lawn care by this time. Fall will be dry if there aren’t many tropical depressions, and turf still needs to store food now for the long winter dormancy.

–Keep an eye out for yellowing areas that would indicate brown patch disease. Treat these with fungicide as needed. Remember, if these areas die off in the late fall, they will still be dead next spring.

Koske gives one last warning: "Too much of a good thing often is bad," he says, explaining, "Excessively high rate of potassium fertilizer may lead to foliage burn (salt burn) or can lead to competitive inhibition of other soil nutrient uptake."

He adds that this is especially known to affect magnesium uptake, which can appear as a light green lawn color.

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Contact: Tom Koske (225) 578-2222 or tkoske@agcenter.lsu.edu
Writer: Mark Claesgens (225) 578-2939 or mclaesgens@agcenter.lsu.edu

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