Lawn Fertilization in Texas

Lawn quality is generally measured in terms of color, density and uniformity. Cultural practices, particularly fertilization, largely determine lawn quality. A fertilization program should include timely fertilizer applications in amounts and formulations that meet the requirements of your lawn. Excessive nitrogen applications stimulate production of leaves and stems and increase the mowing requirements. Higher water requirements, increased thatch and increased susceptibility to insects and diseases also results from excessive application of nitrogen. Poor timing of fertilizer applications, such as mid-summer and early fall applications of soluble nitrogen, also increases the likelihood of chinch bug and brownpatch problems in St. Augustine lawns.

Fertilizer Requirements

The amount and formulation of fertilizer to apply depends on soil test results, grass species, environmental conditions and mowing practices.

Soil tests provide information on the availability of major fertilizer nutrients. Some soils contain phosphorus and/or potassium in amounts adequate for the maintenance of turfgrasses. Additional applications of these nutrients through fertilization would not improve the quality of the lawn. On the other hand, grass growing on soils deficient in one or more of these nutrients will respond to fertilizers containing these nutrients. Soil tests also suggest the need for lime or other Environmental conditions such as shade, soil type and rainfall also influence fertilization requirements. Moderately or heavily shaded areas should not be fertilized as much as areas in full sunlight. Grass growing in shade is more succulent and has a weaker root system than grass growing in full sunlight. Fertilizer tends to make the grass more succulent and increases its susceptibility to disease, drought and other stresses. Nitrogen fertilizer also stimulate leaf growth at the expense of the root system. St. Augustine growing in moderate to heavy shade should be fertilized in the spring and fall only, at a rate of 1 pound of nitrogen per 1,000 square feet.

Turfgrasses growing in sandy soils require more frequent applications of nitrogen than those growing on clay soils.

Lawns in areas subject to high rainfall require more total pounds of nitrogen per year (the higher numbers in the above table) than lawns grown under dry conditions (the lower numbers in the table). Thus, St. Augustine lawns in East Texas may require 4 to 5 pounds of nitrogen compared to 1 pound in Southwest Texas.

Mowing practices, such as regular removal of grass clippings, also influence fertilizer requirements. Grass clippings contain 3 to 4 percent nitrogen on a dry weight basis, which is recycled through the soil if grass clippings are not removed. Regular removal of grass clippings will add at least one fertilizer application annually to lawn requirements.

Fertilizer Applications

Timing and distribution of fertilizer applications, as well as rate of application, are important considerations in a lawn fertilization program. Timing applications to corresponds to grass requirements rather than to the convenience of the homeowner can reduce maintenance problems.  Generally, spring and fall fertilizer applications are adequate for St. Augustine lawns.

In early spring there is usually enough residual nitrogen to maintain grass through several mowings. The first application of fertilizer should be made after the second or third mowing.

If the lawn appears vigorous and healthy at that time, delay the first application until May. In the absence of soil test information, apply a fertilizer with a 3-1-2 or 2-1-1 ratio at a rate equivalent to 1 pound of nitrogen per 1,000 square feet.

Bermudagrass lawns require supplemental applications of nitrogen at 45- to 60-day intervals between spring and fall fertilizations. These applications should not exceed 1 pound of nitrogen per 1,000 square feet per application. .Occasionally, St. Augustine grass may need a supplemental application of nitrogen to enhance color during the summer. Use organic or slow-release nitrogen sources on lawns during the summer. Summer fertilization of St. Augustine grass growing in moderate shade should be avoided because of increased disease activity.

St. Augustine lawns may require periodic applications of iron sulfate or iron chelate to prevent iron chlorosis. A foliar application of iron sulfate at a rate of 6 to 8 ounces per 1,000 square feet effectively eliminates the symptoms of iron chlorosis. These applications may be needed several times during the growing season.

Type of Fertilizer

Choice of the type and grade of fertilizer material to use depends on soil test recommendations. Table 1 shows some analysis, ratios and equivalent applications rates of various fertilizers. In every fertilizer analysis (such as 12-4 8), the first number represents the percent nitrogen (N), the second number represents the percent phosphorus (P2O5) and the third number represents the percent potassium (K2O).

Table 1.Nutrient content and equivalent rates of application of some commercial fertilizers.

¹Or pounds of nutrients per 100 pounds of fertilizer.

A complete fertilizer can be used in accordance with soil test results for the spring and fall applications. Additional nitrogen needed between the fall and spring applications for complete fertilizer can be supplied from one of several sources, as shown in table 2. Slowly available sources of nitrogen, such as ureaformaldehyde, IBDU, processed sewage sludge or cottonseed meal, are more desirable for summer applications of nitrogen than soluble sources such as ammonium nitrate, urea or ammonium sulfate. Slow-release and organic fertilizers usually cost more, but they are available to the grass over a longer period of time and help avoid the excessive growth produced by soluble nitrogen fertilizers. Soluble nitrogen sources should be applied in small amounts and more frequently than slowly soluble or slow-release types. Also, soluble nitrogen fertilizers are more likely to burn the grass than slow-release nitrogen fertilizers.

Table 2.Percent nitrogen in various nitrogen sources, and recommended rates of application for lawns.

¹Pounds of nitrogen in 100 pounds of fertilizer.