Winterize Lawn With Potash Not Nitrogen

Thomas J. Koske  |  9/7/2007 8:28:14 PM

News You Can Use Distributed 08/29/07

To winterize Southern, warm-season lawns, apply a fertilizer with more potash than nitrogen. Potash (potassium) is represented by the third number on a fertilizer bag, while nitrogen is shown as the first. A commercial example is one company's offering of 8-8-15 WINTERIZER. Be aware that not all "winterizers" are the same; some are made for northern cool-season grasses and are still sold here.These northern styles have high N and lower K. Buyer beware!

In the fall, the emphasis in feeding changes from growth to strength. In September, apply a fertilizer with less nitrogen to slow growth and more potash to build stress tolerance.

"Our lawn grasses are the warm-season type, so they grow when it’s warm and not much when it’s cool. That means we must encourage growth with nitrogen in warm weather and not push the grasses when we shouldn't," said LSU AgCenter horticulturist Dr. Tom Koske.

"The ‘shouldn't’ time is fast approaching," the horticulturist said.

A general, complete lawn fertilizer has three major nutrients listed in this order: nitrogen (N), phosphate (P2O5) and potash (K2O) for feeding N,P,and K.

"If we keep feeding a relatively high N in the fall, we will promote soft, lush growth," Koske said, explaining that soft growth is more subject to diseases like brown patch and freeze damage. This damage won’t have time to grow out of it because the cooler weather and shorter days won’t let it.

"Our fall lawn care plan should encourage only moderate, slow growth on centipede, Bermuda, zoysia and St. Augustine lawns," Koske said.  Apply any fall fertilization in September. It is not needed any longer in October.

If you already have been applying about half as much potash as N, winterizing is usually not necessary. If you have been putting out mostly N this summer, apply a southern winterizer now or just muriate of potash (0-0-60) at 1 to 2 pounds of muriate per 1,000 square feet.

"If in doubt, it is better to do nothing at all than do the wrong fertilizer program at this fall transition time," Koske said.

Another important fall chore is to clear leaves from the turf surface to avoid blocking sunlight. Also, maintain adequate moisture during this typically dry season to sustain slow but solid growth. In addition, raise the cutting height a notch except with centipede grass to get more leaf area for more stored food. One chore you don’t have to do, however, is aerify or dethatch this late in the year; wait until late spring or summer.

If pests show up, get on them. Damage from disease or insects will hurt the turf’s ability to store food for winter survival. Many times we are tempted to say, "Oh well, it’s going to turn brown soon anyway."

If the diseased areas die and brown out this fall, expect the dead areas to still be dead next spring. Allow grass to go dormant in a healthy, sturdy state for a healthy spring greenup.

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