When to Put Nitrogen on a Lawn

Application Time

• The first application of nitrogen should be made as soon as the grass starts to grow in spring, the end of April. Make second, third and fourth applications at an interval of every four to six weeks for a total of four applications a year. Avoid applying nitrogen during July and early August, when the use of the fertilizer stimulates the growth of warm-season weeds like crabgrass. The last application should be in early October. In his book "Gardening in the Upper Midwest," Leon Synder suggests applying nitrogen on May 1, June 15, August 15 and October 1.

Application Rate

• The general application rate for nitrogen is 4 lbs. of actual nitrogen for every 1,000 square feet of lawn per year, as recommended by the University of California Extension. That's 1 lb. of nitrogen at each of four feedings. The application rate is similar for both warm- and cool-season grasses. Applying more than a pound of nitrogen at any one time increases the risk of burning the grass.

Quick Release

• Quick-release or soluble forms of nitrogen are available to the grass almost immediately after application. Quick-release nitrogen types commonly used in lawns include ammonium nitrate, urea and ammonium sulfate, which quickly improve the color and growth of turfgrass. Quick-release formulas are also less expensive as compared to slow-release formulas.

Slow Release

• Slow-release formulations need time to break down in the soil before the nitrogen is available to the grass. To minimize loss through leaching, slow-release nitrogen needs to be applied properly. These formulas are more well-suited for lawns growing in sandy soils and can safely be applied at a higher rate without danger of burning. Slow-release nitrogen includes natural organics, urea-formaldehyde and sulfur-coated and polymer-coated ureas.