Dr. Grow: Balancing the elements

In my last column I explained what lawn seed to use in different situations. Today I want to explain what fertilizer to use when seeding a lawn and also discuss the use of lime and the seeding process.

Fertilizers are required by law to be identified by their contents of nitrogen (N), phosphorous (P) and potassium (K), in that order. There is an old horticulture rule of thumb that says NPK refers to shoots, roots and fruits. In other words, a fertilizer with high concentrations of N will promote shoot or top growth. A fertilizer with high concentrations of P will promote root growth.

You need to use a fertilizer that has a low N concentration compared to the P concentration when you seed a lawn. You initially want to promote good root growth so that new grass seedlings can get a good roothold. Use a new lawn starter, such as 9-13-7. It is also important to make sure that the soil pH is adjusted to near neutral when seeding. Take a soil sample to your local University Extension Center. They will (for a nominal fee) send the sample to their lab in order to determine the soil pH. Most soils in our area are acidic (have a low pH).

To reduce acidity you must add lime to the soil. A good time to add lime to the soil is at the time of seeding. The amount of lime you need to add will be determined by the results of the soil test. You may need to add from one to 200 pounds of lime per 1,000 square feet. The soil test results will tell you how much to use. If you have your soil tested but do not understand the results, take your results to your local garden center. They should be able to tell you how much lime you need to add to your soil for optimum results.

Why is soil pH so important? The pH determines the availability of soil nutrients to plants. If the soil pH is not correct, a particular soil may have all kinds of nutrients in it, but the nutrients will not be available for plants to use. In effect, the plants will starve because the soil will not give up its nutrients.

Now let's get to the actual seeding process. I am going to assume that your lawn is at the proper grade level and that you are going to overseed an existing lawn. First, spread seed, fertilizer and lime, if needed, at the recommended rates over the entire area to be seeded. Use a cyclone-type spreader for best results. Next, run a verticutter over the seeded area in two or three different directions. A verticutter can usually be rented from your local equipment rental store. The verticutter cuts grooves into the soil and forces the seed into the soil. If you do not use a verticutter, then most of the seed that you spread will lay on top of the soil. The germination percent will be very low. It is imperative that you get the seed into the soil so that the germination percent is very high. Using a verticutter will accomplish this.

After verticutting, cover bare areas with a light application of straw. The straw keeps moisture in the soil and reduces the problem of soil erosion.

After strawing, start watering your newly seeded area. Make sure that after the initial watering the soil does not dry out. This may require watering once a day or even two times a day if the weather is hot and windy. Keep up the watering until the new lawn has been mowed once or twice.

It is important that you mow your new grass plants when they are three to four inches tall. Do not let your lawn get six to eight inches tall. Mowing will encourage the new plants to mature.

After you have mowed your lawn one or two times, it is important that you fertilize the lawn again. This time use a standard lawn fertilizer. The N should be very high, while the P and K should be very low. A good example would be a 28-4-4. Remember the new lawn starter encourages root growth. Now you want to encourage top growth.

If you follow the directions I have outlined in this and the previous column, you should have a good lawn in about six weeks. In fact, if you start now, you could have a great-looking lawn before Halloween.

Paul Schnare of Cape Girardeau has been in the lawn and garden business for more than 20 years. He's an adjunct professor in horticulture at Southeast Missouri State University.