Early to mid-September is the most important time to fertilize cool-season turfgrasses like creeping bentgrass, Kentucky bluegrass, perennial ryegrass, and tall or fine fescue. September fertilization is crucial on all turf areas regardless if it is a lawn, athletic field, or golf course green, tee or fairway. Fertilization in mid-September encourages the production of new tillers and/or rhizomes and stolons that will increase the density of a turf. Fertilization in September also encourages rooting and production of storage products that will help the plant survive the stresses of winter and next year’s growing season. Once the temperatures start to cool in the first week or two of September, most turf areas should be fertilized with 1 lb N/1000 sq ft using a fertilizer with 25-50% of the nitrogen as slow release (sulfur or polymer-coated urea, urea formaldehyde, or natural organics). More fertilizer information is available in AY-22: Fertilizing Homelawns.