Lawn fertilizers are plant nutrients; ordinarily, nitrogen (N), phosphorus (P), and potassium (K). These are the N, P, and K listed on the label of fertilizer packages. Lawns usually require more nitrogen to promote growth, but this need varies. Lime is applied to correct soil acidity. It is an amendment or conditioner, not a fertilizer. Acid souls are said to be "sour." Alkaline soils are called "sweet."
Fertilizer contains nutrients that help give grass color, prevent disease and weed invasions and enable grass to recover from drought and other stress. Grass usually needs nitrogen the first number on a bag of fertilizer. Horticulturists at the University of Illinois recommend 3-1-2 or 4-1-2 fertilizer for lawns. Those numbers indicate the percentage by weight of N, P, and K.
Fast-release fertilizers, including urea, ammonium nitrate and ammonium sulfate, are inexpensive, respond quickly, and yield nitrogen when the soil is cold. They are also more likely to burn the grass or be lost through the soil or air. Slow-release fertilizers give more uniform growth of grass and are unlikely to burn, but they are more expensive and might not work on cold soil.
The amount of nitrogen needed by lawns depends on the grass. Kentucky blue grass and perennial rye grasses do best when fertilized regularly. Common blue grasses combined with fine fescue grow more slowly and don't need as much nitrogen. In most cases 1 pound of nitrogen should be applied for every 1,000 square feet of lawn. If the fertilizer contains a high percentage of nitrogen, less fertilizer is needed. Follow the instructions on the label.
The pH of a soil measures the amount of hydrogen ions in the soil. These amounts are numbered between 1 and 14. Seven is neutral. Soils with a pH of less than 7 are acidic; those greater than 7 are alkaline. Most lawn grasses grow best between pH 6.5 and 7. An acid soil indicates a low amount of calcium and magnesium. That is why lime is applied to acid soils. Contact your state agricultural extension service to find out how to get your soil tested, the first step in determining whether or not your lawn needs lime.
Benefits of Lime
Lime furnishes calcium and magnesium, and makes aluminum, manganese and iron less soluble and toxic. Calcium helps regulate copper, zinc and phosphorus. Lime also increases the activity of bacteria needed to decompose organic matter, making the soil more porous and increasing air and moisture in the soil. If a soil has proper pH, made possible in some cases by adding lime, it is better able to use the nutrients in fertilizer.
Types of Lime
Ninety-five percent of American lawns are limed with ground limestone and finely ground calcium carbonate. It is widely available, cheap, and not caustic.
Burnt lime, calcium oxide, is also called quick lime; it's strong, acts quickly and can burn. You need to wear gloves when handling it. Hydrated lime is when calcium oxide is mixed with water. It too is strong and can burn.
Time to Apply
The best time to apply lime is in the fall; winter is second best; spring is third best. Wet soil makes it hard to distribute lime evenly. Sandy soils require less lime than soils high in clay or silt. A soil test will help determine the best rate of application. Lime should not be applied more than once every three to five years.