Good maintenance for the home lawn requires proper mowing, watering, and fertilization. Fertilization is the activity that causes the most concern for conscientious homeowners. Selecting the best packaged fertilizer based on price and composition is a daunting task because of the wide variety of available choices. We should do better than just follow rough generalizations such as "add more nitrogen to make the top greener and more potassium to make the roots grow" or even "apply fertilizer at a rate to give one pound of nitrogen per 1000 square feet of lawn." We must also decide when to apply, whether to apply with drop or broadcast spreader, whether to water it in, and how the fertilizer will affect other garden plants. The package label provides much useful information and should be read carefully.
Fertilizers are labeled with three numbers representing amounts of the three major nutrients: nitrogen (N), phosphorus (P), and potassium (K). A fertilizer labeled 15-5-10 includes 15 weight percent N, 5 weight percent P, and 10 weight percent K. Note that the ratio of N-P-K in this example fertilizer is 3-1-2. The remaining 70 weight percent can be other ingredients such as iron, sulfur, weed killers, insect pest killers, fungicides, and inert fillers. The inert fillers are frequently salts that can build up in the lawn.
Too much nitrogen (N) makes the grass green but also causes leaves to grow fast, thereby requiring excess mowing and watering. Too much phosphorus (P) can tie up the iron in the soil, causing the grass to turn yellow even when nitrogen is adequate. The less expensive fertilizers have a very water-soluble form of nitrogen that is released immediately to the grass, causing it to be consumed rapidly and/or lost in run-off. Some more expensive fertilizers have the nitrogen chemically modified so it is released slowly to the plants. This can result in the grass remaining suitably green with less mowing, less watering, and less frequent additions of fertilizer. This also results in less build-up of salts in the lawn and less run-off of nutrients into the environment beyond the lawn. These advantages can make the initial high cost worthwhile.
Consider buying package lawn fertilizer with at least 50% of the nitrogen in slow-release form and applying it at a rate based on guidance from a nurseryman familiar with your neighborhood or, even better, based on a soil test. Check with your county Extension agent with Texas Cooperative Extension about obtaining a test for your soil from Texas A&M for about $13. The test results will enable you to select a fertilizer with the correct nutrient components, in the correct ratio and quantities, for your particular lawn.
Bill Gates, Smith County Master Gardener
Texas AgriLife Extension Service