Turfgrass management in late summer and early fall is extremely important. Proper practices can help maintain a vigorous lawn or revive a declining lawn. These practices include mowing, fertilization, dethatching, aeration, weed control, and seeding.
Mowing. Mowing produces a neat, well groomed appearance. However, improper mowing causes many lawn problems. The cool season grasses, such as Kentucky bluegrass, perform best in the cool weather of spring and fall. Bluegrass lawns are typically mowed at a height of 3 inches during the hot, stressful summer months. Lower the mower blade as temperatures cool in late summer. Mow bluegrass at 2 to 2 1/2 inches during fall. Mow often enough so that no more than 1/3 of the total leaf surface is removed. Continue mowing the lawn until it stops growing and becomes dormant in late fall (early to mid-November).
Mow newly seeded bluegrass lawns at a height of 2 to 2 1/2 inches as soon as it reaches 3 to 3 1/2 inches in height. Mowing doesn't hurt the grass, it encourages spreading and promotes a thicker lawn.
Fertilization. Late summer and fall is an excellent time to fertilize lawns. Apply 1 to 2 pounds of actual nitrogen per 1,000 square feet.
Thatch Removal. Thatch is the layer of dead and living plant material that forms between the soil surface and green foliage. When thatch is present in amounts greater than 1/2 inch, dethatching may be beneficial. Vertical mowers and power rakes, available from many rental companies and garden centers, thin the grass and lift the thatch to the soil surface. The debris is then raked from the lawn and discarded. Thatch removal can be done in late August or September. Allow at least four weeks of good growing weather following dethatching. This gives the turfgrass time to recover before it becomes dormant in the late fall. Apply fertilizer after dethatching to promote recovery of the turfgrass.
Aeration. Lawn areas subject to heavy foot traffic may be thin due to compaction. Aerify compacted soils in late August or September with a machine that has hollow metal tubes or tines that remove plugs of soil from the lawn. Avoid spike-type devices that simply punch holes in the turf. Break up the soil cores by raking or mowing after aerification. Then apply fertilizer to promote recovery of the turf.
Broadleaf Weed Control. Perennial broadleaf weeds, such as dandelions and plantain, can be controlled with the application of broadleaf herbicides from mid-September to early November. Most broadleaf herbicide products consist of a mixture of two or three of the following chemicals: 2,4-D, dicamba, MCPP, and triclopyr. Fall applications of broadleaf herbicides are safer and more effective than spring or summer applications. During the fall, perennial weeds translocate carbohydrates down to their roots. If a broadleaf herbicide is applied to the weeds, it will also be translocated to the roots, resulting in the complete destruction of the weeds. With gardening activity winding down in the fall, the risk of injury from herbicide drift to vegetable and flower gardens, fruits, and ornamentals is also reduced.
Seeding. Late summer or early fall is an excellent time to establish new lawns or overseed thin or severely damaged lawns. Seeding may begin in mid-August and should be completed by September 30.
This article originally appeared in the July 29, 1994 issue, p. 123.