Lawn Fertilization

Fertilizing is an important lawn care practice in the Midwest. Nitrogen, Phosphorus, and Potassium are the three major nutrients needed by lawns. Nitrogen is the nutrient required most, although too much can also cause an assortment of problems. In most cases, a rate of one pound of nitrogen per 1,000 square feet is suggested for each fertilizer application. The total amount of nitrogen should be spread over the growing season. The schedule found below outlines when to apply fertilizer based on how many applications are to be made annually and the desired lawn schedule.

To determine the amount of product to apply you need to know the analysis of the fertilizer product. For example, a 20-6-12 fertilizer contains 20 percent nitrogen. One pound of a 20-6-12 thus contains 0.20 pounds of nitrogen. To obtain a rate of one pound of nitrogen per 1000 square feet, an application of 5 pounds of 20-6-12 would need to be used on 1,000 square feet.

Number of Applications/Year Suggested Timing
One (Low Quality Lawn) Early September
Two (Moderate Quality Lawn) Early May
Early September
Three (High Quality Lawn) Early September
Late October
Four (High Quality Lawn) Early May
(With Irrigation Only) Mid June
Early September
Late October

If the soil test for nitrogen is high, the suggested timing of the applications may be reduced or skipped. This is normally stated on the report. For example, if your soil test contains 50 pounds of nitrogen, the next application of nitrogen scheduled can probably be skipped. A soil test of 50 pounds per acre is equivalent to one pound of nitrogen per 1000 square feet.

Research has shown the benefits of late fall fertilizer after grass growth has about stopped but the lawn is not yet dormant. In most cases, avoid fertilizing the lawn during the hot weather months of July and August. You may consider using a controlled-released nitrogen fertilizer in May and September and a fast-release source in late fall.