Fertilizing Lawns - HGIC@clemson.edu

Essential Elements

All plants require certain chemical elements for proper growth and appearance; at least 17 of these elements are essential. Table 1 lists these 17 essential elements and their sources. All essential elements, except carbon, hydrogen, and oxygen, are sourced from the soil and absorbed by plant roots. Limited soil nutrients can restrict lawn growth and quality, but adding fertilizers can supplement these essential elements.

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Table 1. Essential Elements Required by Lawn Grasses (From Southern Lawns).

Lawns require significant quantities of macronutrients nitrogen (N), phosphorus (P), and potassium (K). While calcium, magnesium, and sulfur are also essential, they are needed less frequently and in smaller amounts.

Dolomitic limestone, a major source of calcium and magnesium, not only reduces soil acidity but also supplements fertilizers. Micronutrients like iron, manganese, zinc, boron, copper, chlorine, molybdenum, and nickel are needed in trace amounts but are just as vital. Table 2 outlines these essential elements categorized by their nutrient type.

Types of Fertilizers

Fertilizers are identified by their nutrient analysis or brand name. Commonly, commercial fertilizers are known by nutrient ratios such as 16-4-8, 10-10-10, or 15-0-15, indicating the percentage of nitrogen, phosphate, and potash in them. For example, a 16-4-8 fertilizer contains 16% nitrogen, 4% phosphate, and 8% potash. These three are primary plant nutrients, and fertilizers containing all three are considered complete fertilizers.

Complete fertilizers like 16-4-8, 12-4-8, and 18-24-6 are commonly recommended for lawns. Incomplete fertilizers, which lack one of the macronutrients, can be used when specific nutrients are unnecessary or to supplement a missing nutrient. Examples include 15-0-15, 21-0-0, and 34-0-0. Table 2 lists primary, secondary, and micronutrients.

Table 2. Listing of Primary, Secondary, and Micronutrients.

Besides primary elements (N, P, and K), fertilizers may contain secondary nutrients like calcium, magnesium, sulfur, iron, manganese, zinc, copper, and molybdenum. Both primary and secondary elements are listed on the fertilizer label, along with information on the materials it is derived from. An example of a mixed fertilizer containing various nitrogen sources is shown in Table 3.

Table 3. Example of a Fertilizer Label (From Southern Lawns).

Some materials are almost exclusively used to supply nitrogen to the lawn for rapid growth and a dark green color. These include ammonium sulfate with urea (34% N), ammonium sulfate (21% N), calcium nitrate (15.5% N), IBDU (31% N), urea (45% N), and ureaform (38% N). Nitrogen fertilizers may be applied more frequently than complete fertilizers if necessary.

The best yearly fertilization program is based on soil analysis and typically includes a combination of complete fertilizers and additional nitrogen applications. Complete fertilizers supply nitrogen, phosphorus, and potassium, while nitrogen materials primarily supply nitrogen. Phosphorus and potassium rates should be guided by soil sample analysis and recommendations. For details on soil testing, refer to HGIC 1652, Soil Testing.