Fall Lawn Care

11 August 2008

Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580   fax: 434.872.4578

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The change in seasons from summer to fall presents the optimal time for the renovation and establishment of cool-season turfgrasses. Warm days and cool nights provide ideal conditions for seed germination and establishment of tall fescue, Kentucky bluegrass, fine-leaf fescues, and perennial ryegrass. Sod establishment is also favored at this time of year.

A photo of Kentucky bluegrass turf in need of aeration.

The first step towards correcting an existing problem lawn or establishing new turf is to test your soil. This very cost-effective diagnosis of your soil’s fertility and pH status is quite often the answer to the question of “Why did my turf fail?” Many Virginia soils are very acid and probably require a supplemental lime application. The fall and winter months are ideal times to make lime applications since it takes weeks to months to fully realize the benefit of the treatment. It is a good idea to test your soil at least once every three years to determine if supplemental nutrients other than nitrogen are required. Since growing conditions are ideal at this time of year, grasses respond quickly to test-recommended applications of fertilizer and lime.

For new plantings, tilling the soil to a 4- to 6-inch depth is desirable prior to seeding. This gives you an opportunity to put the information from a soil test to work and incorporate any recommended lime or starter fertilizer that will aid turf establishment. A starter fertilizer emphasizes phosphorus (P) levels as compared to nitrogen (N) and potassium (K) and the typical nutrient ratios of N-P-K in these sources are 1:2:1 or 1:2:2. It is equally important to provide some degree of soil preparation even for overseeding into existing turf. A few passes with a coring machine (often called an aerator) or a vertical mower (often called a dethatcher) can be used to prep the soil prior to planting to encourage seed-to-soil contact. Simply applying seed over the top of an existing turf without any soil preparation usually does nothing more than feed wildlife, birds mostly.

After planting, irrigate lightly and frequently until seed germination is complete. Avoid excessive amounts of water because this could either wash away or drown the seed. As establishment progresses, gradually cut back on the amount of water you apply in order to start promoting a deep root system. The irrigation philosophy is similar for sod establishment, but larger amounts of water can be applied less frequently because sod provides soil and root mass that hold moisture.

Mow turf when it needs to be clipped according to its recommended cutting height and follow the mowing rule that says you never remove more than one-third of the leaf blade at any mowing event. For example, the recommended lawn height for tall fescue is 3 inches. So begin mowing as soon as your new lawn reaches a 4-inch height. Be sure the mower blade is sharp and the soil surface is firm.

You can make supplemental nitrogen applications later in the fall after establishment if you want a boost in growth or color. Remembering the acronym “SON” (representing the months of September, October, and November) can help you make a smart decision on when to apply nitrogen to cool-season turfgrasses. This fertility program is ideal for maximizing the benefits of nitrogen fertilization. The fall presents growing conditions conducive for improving turf density through the development of new shoots and stems, increased carbohydrate storage (i.e. food for the plant), and enhanced root production. Applications of 1/2 to 1 pound of water-soluble nitrogen per 1000 square feet on 4- to 6-week intervals are very beneficial during this time, much more so than programs that emphasize heavy spring fertility. Similarly, an early to mid-September application of a controlled release nitrogen source (a material that contains > 50 percent water-insoluble nitrogen) at levels of 1.5 to 2 pounds nitrogen per 1,000 square feet provides similar benefits. It is possible in many locations that a single fall application will suffice to meet the needs of your turf.

Periods of active growth are ideal times to cultivate turf. Core aeration and vertical mowing are two methods of turf cultivation that can provide long-term benefits if done properly and at the right time of year. Any soil that is heavily trafficked is likely to have some degree of compaction that is limiting root development. Compaction physically restricts root penetration and reduces soil oxygen levels required for root development. Core aeration (removing plugs from the soil in a process often called “aerifying”) is a standard method for improving soil aeration. Vertical mowing (often referred to as “dethatching”) physically removes thatch, a layer of undecomposed stems and other living and decaying organic matter that develops between the soil and the turf canopy. Vertical mowing is not intended to relieve soil compaction or improve soil aeration. Thatch layers greater than 1/2 inch should be removed to improve turfgrass performance. Fortunately, most cool-season turfgrasses will not develop a significant thatch layer, but a creeping grass like Kentucky bluegrass grown under a moderate to high level of management is likely to develop a thatch layer over time. Check on the depth of thatch in your lawn when removing soil samples.

Obviously, each of these activities is highly disruptive to the soil surface and the turf itself. Both initially cause stress to the turf due to the physical tearing and severing of shoots, roots, and stems. Ultimately, the benefits of the cultivation treatment greatly outweigh these concerns, but it is wise to refrain from aerifying or dethatching cool-season turfgrasses until the fall when turf recovery can be optimized by fertilization and irrigation or rainfall.

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For more information about this and other landscape topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.