Ronald Strahan, Koske, Thomas J. | 5/16/2007 1:24:29 AM
Louisianians who winterize their lawns in October need to be especially careful at reading the nutrient label on the fertilizer bag, according to LSU AgCenter horticulturist Dr. Tom Koske.
"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."
In his own experience, the horticulturist found a local retailer selling three different kinds of winterizing products - all formulated for northern grasses. These winterizers had a fertilizer analysis with high nitrogen (N), first number on the product bag, and lower phosphorus (P) and potassium (K), 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 K enhance tolerance to a broad range of environmental stresses including cold damage. Therefore, a good strategy is to maintain high levels of soil K throughout the growing season and especially in the fall.
"With high K 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 (P), the middle number on a fertilizer bag, is not critical. It promotes winter annual weed germination, Koske explains.
"Just use muriate of potash (0-0-60) or do nothing," the LSU AgCenter horticulturist advises. Apply potash at 1 to 2 pounds per 1,000 square feet.
He warns, however, "Too much of a good thing is often bad. An excessively high rate of K fertilizer may lead to foliage burn (salt burn) or can lead to competitive inhibition of other soil nutrient uptake."
The LSU AgCenter and the LSU College of Agriculture