The second primary cultural practice is fertilization. Maintaining adequate levels of nitrogen and monitoring soil pH are important for a successful IPM program. Nitrogen is the primary nutrient, and turfgrass will require substantially more nitrogen annually than any other nutrient. Depending on the species 2 to 6 lb N per 1,000 sq ft are recommended annually. Tall fescue, fine fescue and bentgrass will require low amounts of nitrogen (2 lbs N per 1,000 sq ft annually), while Kentucky bluegrass and perennial ryegrass will required high amounts of nitrogen (4 to 6 lbs per 1,000 sq ft annually). A maximum rate of 1 lb N per 1,000 sq ft can be applied in a single application. Applications should be made in the spring and fall months. The other primary nutrients are phosphorous (P) and potassium (K); therefore, it is advantageous to select a fertilizer with these nutrients as well. Fertilizer applied to established lawns should have high amounts of N, low amounts of P and moderate amounts of K, such 25% N - 3% P - 10% K.
Do not apply fertilizer containing P near water sources in late fall or winter, to limit the risk of runoff. In an effort to protect water quality, it is now a best management practice in the state of Washington for homeowners and publicly owned turfgrass areas to conduct a soil test before they are allowed to purchase a turf fertilizer containing phosphorus. In this circumstance soil testing should be conducted once every three years.
Removal of clippings during mowing significantly increases fertilizer requirements. Tests indicate from 25% to 50% of applied N may be removed with clippings. Removing clippings may deplete nutrients in soil and ultimately lead to loss of turf density and increased weed invasion. It is good to return clippings to the site when possible. It can add back enough nitrogen to back off on one of your fertilizer applications if you have been fertilizing appropriately.