Mulch provides a variety of benefits to these crape myrtles at the LSU AgCenter Burden Center in Baton Rouge. (Photo by Allen Owings.)

News Release Distributed 09/23/11

By LSU AgCenter Horticulturists Dan Gill, Kyle Huffstickler and Allen Owings

September begins the transition to cool weather and fall activities in the Louisiana landscape. It is important to get started with cool-season flowers and bed preparation, assess your lawn status, consider mulching for trees and shrubs, and more.

The season for cool-season plants starts in September. Although it may be most ideal to plant most cool-season bedding plants in October, petunias would not mind being planted now. Late September is a great time to start planting petunias, which can be continued into early to mid-October. Try the Wave, Easy Wave and Tidal Wave petunias if you really want to make an impression.

Some other bedding plants recommended for fall planting in Louisiana include pansies, violas (johnny jump ups), dianthus, calendula, snapdragons, stock and flowering kale or cabbage. Check your local garden centers for bedding plant varieties that are available. Most of these do best when planted mid-October through November. But September is the time to start by cleaning up any debris from your warm-season flowerbeds and preparing the beds for planting in October.

Do a soil test if you suspect pH problems. Ideal pH for many bedding plants is 5.5–6.0. This is considered to be an acid soil and is similar to the pH preferred by azaleas and gardenias.

September is an important month in home lawn care. Many of us may want to apply additional fertilizer to the lawn to "keep it going" through fall – but this needs to be avoided. Putting nitrogen fertilizer on warm-season lawn grasses after early September is not recommended. The nitrogen will stimulate growth that will be prone to disease during fall and cold damage during the coming winter.

Many times a fall application of a “winterizing” fertilizer is recommended. This is a good idea in some cases. A winterizing fertilizer for home lawn use in Louisiana has a low amount of nitrogen (the first number on the fertilizer bag), a low amount of phosphorus (the second number on the fertilizer bag) and a high amount of potassium (the third number on the fertilizer bag). Never use a winterizing fertilizer that has more nitrogen than potassium. Fertilizers with these ratios are recommended for fall application to cool-season grasses and are not for use in Louisiana (even though these fertilizers are sold here).

A potassium application in the fall is recommended only when a soil test of your home lawn area indicates low or medium levels of potassium in the soil. If you have high or very high levels of potassium, a fall application of potassium is not needed. If you apply potassium, do it at the rate of 1-2 pounds of actual potassium per 1,000 square feet of lawn area.

You may notice brown patch disease on your lawn during September. This disease is characterized by circular, brown patterns that will green back up on the inside as the circle extends outward. Contact your local LSU AgCenter county agent for current fungicides recommended for this disease. Controlling brown patch in the fall yields improved green-up in the spring.

If you are considering overseeding your lawn with a cool-season grass, such as ryegrass, wait until late October through mid-November, depending on where you are located in the state.

Many of us want to do some pruning in the fall. When you prune, use thinning-type cuts instead of topping your plants. Wait until later in the fall or even until winter to prune most trees, such as crape myrtles. Sometimes pruning stimulates new growth, which we need to avoid in fall due to the possibility of cold damage.

September also is an ideal time to add a new layer of mulch to your landscape beds. What does mulch do for our landscape plants? It minimizes soil temperature fluctuations, controls weed seed germination and subsequent growth, adds organic matter to the soil and plays a major role in moisture conservation. Mulch also insulates the lower stem and root system of the plant from cold winter temperatures and hot summer temperatures.

The best mulch is pine straw. Mulch trees to a depth of 3 inches and shrubs to a depth of 2 inches. Avoid piling the mulch around the base of the stems.

Working in your landscape in September will properly prepare your plants for the rest of the fall.

Visit LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is near the intersection of Burbank Drive and Nicholson Drive (Louisiana Highway 30) in Baton Rouge, across the street from the LSU baseball stadium. For more information, go to www.lsuagcenter.com/lahouse or www.lsuagcenter.com/lyn.

Rick Bogren