A lawn is a long-term proposition. Because grass roots use the same soil year after year, soil nutrients will eventually be depleted. You can replace nutrients through a regular program of fertilization.

Three major elements are essential and frequently in low supply in an established lawn: nitrogen, phosphorus, and potassium. Oxygen, hydrogen, carbon, calcium, magnesium, manganese, copper, zinc, and iron are necessary, but these are usually sufficiently abundant in the atmosphere or in the soil. A healthy, living soil is full of trace elements and microorganisms and has good structure, making nutrients available to your lawn.

Nitrogen (N). Of the three major nutrients, nitrogen is the most important to the lawn. It directly affects the rich green color of a lawn. Because nitrogen moves up and down in the soil, it is difficult to maintain a constant, uniform supply without replenishing it regularly. Nitrogen is also subject to leaching from too much water. Large quantities of nitrogen are required by grass plants to maintain vigor following repeated cutting and to keep the lawn looking green and healthy during its long growing season. Lawns lacking nitrogen show stunted growth and a yellowish appearance.

Phosphorus (P). While nitrogen affects the top growth of grass plants, phosphorus is especially important for strong, vigorous root systems and good disease resistance. Because it is bound to the soil particles, this element tends to remain constant in the soil once it has been introduced but can only become available to plants in a living, active soil. Inadequate rooting, off-color, and low growth indicate a phosphorus deficiency.

Potassium (K). is important for grass hardiness, tolerance to heat, cold and traffic. It also increases disease resistance and helps plants absorb food from the surrounding soil. Like nitrogen, it moves in the soil and is leached by water, so replenishment is necessary, at least twice a season.

When purchasing fertilizer, you can choose synthetic chemical-based food or natural organic mixtures.

In general, chemical fertilizers are water-soluble and application results in a rapid response. If applied in excess they can seriously "burn" turf and cause overly rapid growth. They also can lower the soil pH and promote the growth of thatch. Since the chemicals last for a relatively brief time and some wash out of the soil with rain and sprinkling, light applications four times a year are recommended for an effective program.

Organic fertilizers are less easily soluble and therefore release nutrients slowly and evenly over a longer time period. Rarely do they burn grass even when applied at higher than recommended rates. Organic, natural fertilizers may also provide a wealth of soil-building trace minerals, some humus, and microorganisms to help produce a healthy living soil. Usually only two applications are necessary, in spring and fall. Whether you use chemical or organic fertilizer, the late summer or early fall feeding is the most important because grasses make most of their root growth in the fall.

Most fertilizers are "complete," i.e., they contain all three major elements. The label indicates the guaranteed minimum percentages of the three major nutrients. This is always represented by three figures such as 10-6-4, 20-10-5, 10-10-10. These figures refer to the percentage of nitrogen, phosphorus, and potassium, always in that order. Those most commonly used for established lawns are high in nitrogen; those for new lawns are high in phosphorus. Most lawns respond best to a 4-1-2 (organic) or 20-10-5 (chemical) ratio.

Apply fertilizer as evenly as possible. Uneven distribution produces irregular color and growth, and spotty heavy deposits of inorganic fertilizer will burn the turf. Make two passes over your lawn with a mechanical spreader, applying half the total recommended amount in one direction and the other half in a direction perpendicular to the first. Shut the spreader off when making turns to avoid excessive deposits there, and overlap the wheel tracks to avoid skips. Fertilize only when the lawn is dry; water immediately after application.

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C.R.S., Inc. · Spokane, Washington · USA