Winterizing Your Southern Lawn

Ronald Strahan, Koske, Thomas J.  |  5/25/2005 11:02:57 PM

Warm-season growth calendar.

Rhizoctonia Large Patch (Brown Patch).

Remove fallen leaves to compost pile.

The term winterize, when used in warm-season grass lawn care, is simply stated as slow down growth and beef up plant levels of the nutrient potassium (K). This is an attempt to toughen plant tissues for the winter freezes much as you would add antifreeze to your car’s radiator for freeze protection.

Winterizing for a cool-season grass like rye or fescue is just the opposite. Here we supply a fertilizer blend that has higher N to resume fall growth and reestablishment after summer dormancy. Be sure you buy the correct kind of winterizer!

Research has shown that higher levels of plant K enhance tolerance to a broad range of environmental stresses, including cold damage. A good strategy is to maintain high levels of soil K throughout the growing season. When soil test levels of K have reached a high level, maintain that by applying about 2/3 part of K2O fertilizer for every one part of nitrogen (N) supplied. This is not an exact calculation, but a general rule. The third analysis number on the bag of fertilizer is the percent by weight of potassium K2O equivalent also called potash.

Phosphorus (P), the middle number (as percent P2O5 equivalent) on a fertilizer bag analysis, does not usually come into play here as long as soil levels are not very low. Extra fall P would just promote winter weed seed germination. An exception is if you will overseed ryegrass for winter color; then you may apply P for better ryegrass seedling development.

With high K available all season, special winterizing would be unnecessary and the turf would be in the best shape to handle environmental and pest problems all season long. Just make sure your last application of N is lower (maybe half rate or less) when applied after late summer and before mid fall. After mid fall, do not apply N to a warm-season lawn.

For those with a less-than-ideal lawn fertility program, here are some end-of-season tips:

  1. Reduce N fertilizing to 1/3 normal application or less. If you don't have a lawn by September, you should not try to continue to grow it out in fall and risk extra winter kill. Reducing N fertility slows growth, which allows the grass to toughen and store more carbohydrate in reserve for spring green-up. Lower fall N also reduces Brown Patch (Large Patch) disease, which is very prevalent in fall.
  2. Finish the growing season with a fertilizer high in potassium. If not using a southern winterizing blend or warm-season grass winterizing blend, at least choose an even ratio analysis like 13-13-13 to avoid high N. If applying only K to avoid extra fall N, use 1 to 2 lbs./1,000 sq. ft. of muriate of potash (0-0-60). This supplies 60% K2O or up to 1.2 lb. K2O/1,000 sq.ft.
  3. Keep up adequate moisture in the fall. We often want to forget lawn care by this time. Fall in Louisiana will be dry without tropical depressions, and turf still needs to store food now for the long winter dormancy.
  4. Watch for yellowing areas that indicate brown patch disease. Treat with a ‘patch’ fungicide as needed. Remember, if these areas die off in the fall, they will still be dead next spring.
  5. Always apply granular materials on dry foliage. This reduces the salt burn potential of an application. They are usually watered in if rain is not expected.
  6. Keep fallen leaves off the lawn. Extended periods of heavy leaf cover are essentially mulching over your lawn. This will reduce the turf’s ability to photosynthesize and make a carbohydrate reserve for storage during dormancy.

One last warning is offered. Too much of a good thing is often bad. Excessively high rate of K fertilizer may lead to foliage burn (salt burn) or can lead to competitive inhibition of other soil nutrient uptake. This is especially known to affect magnesium (Mg) uptake, which can appear as a light green lawn.

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