While the exact fertilizer formulation depends on the soil's specific needs, a good all-purpose fertilizer is a 10-10-10 mix. Applying different formulations at different times in the year gives the lawn a green, lush look year-round.
Begin with a soil test to determine the soil's deficiencies. This test determines the soil's pH and what nutrients are available for the grass to use. Based on the results of that test, choose a fertilizer formula that best meets the lawn's needs.
For a general fertilizer, choose a 10-10-10 variety. This formula contains, by weight, 10 percent nitrogen, 10 percent phosphorous and 10 percent potassium. These nutrients promote growth, a deep green color, a strong root system and protection from drought, disease and cold.
In the spring, use a 20-5-10 mix. The nitrogen will help the grass grow rapidly, while lesser amounts of phosphorous are needed because the root system should be intact in a well-established lawn. The extra boost of potassium helps the lawn prepare for hot and dry summer weather.
In the fall, fertilizing is crucial to help the grass store up the nutrients it needs to make it through winter. Choose a formula with lots of nitrogen to help the lawn continue growing and prepare for winter. Picking a slow-release formula is also important for fall fertilization.