September is the ideal month to improve an existing lawn or to establish a new one. It is the preferred month for fertilizing, weed killing, dethatching, aerating and reseeding.

Fertilization does more to improve a poor quality lawn and maintain a good quality lawn than any other management practice. If fertilizer is applied once a year, this is the month it should be done. This is the time of the year when the grass is increasing in density by forming tillers on most types of grass and rhizomes on blue grass.

About 1½ pounds of nitrogen per 1,000 square feet should be applied at this time. Most lawn fertilizer, when applied according to package directions, will supply about 1 pound of nitrogen per 1,000 square feet. Application of the fertilizer should be made as early as possible in September. Fertilizer should not be applied after Oct. 1. Late application causes the grass to be too lush and tender going into winter and is then susceptible to diseases such as snow mold.

This is the best time of the year to kill weeds. The grass can fill in the thin spots created when the weeds are killed without competition from sprouting summer weeds such as crab grass. This is a disadvantage when killing weeds in the spring. Some weeds, such as clover, are easier to eradicate in early fall because the plants are weak after producing flowers most of the summer.

Most broadleaf weed killers on the market, whether liquid or granules, contain the same three chemicals. The granular type is combined with fertilizer and is generally applied to the whole lawn. The liquid type has the advantage that it can be applied to individual weeds and excessive chemicals are not necessarily being added to the environment.

Lawns damaged by drought and poor turf can be overseeded at this time. However, reseeding without preparation is almost always fruitless. The seed must come in contact with the soil and have space to germinate and develop. This can be accomplished by aeration of 6 to 8 passes with a plug type aerator, dethatching, or by using a disk type seeder that drops seeds into slits in the soil. The seed must come into contact with the soil.

Thatch should be removed when it exceeds ½-inch in thickness. Thatch decreases the vigor of the grass by restricting the movement to air, water, fertilizer and pesticides into the soil. Grass roots also grow into the thatch and become desiccated as the thatch dries. Thatch should not be removed during late fall when winter desiccation may occur.

Maintaining a soil pH of 6.5 to 7.0 can retard thatch build up. This favors microbial activity and breakdown of thatch.

Aeration is used to alleviate soil compaction and can reduce thatch. Aerators remove plugs of soil from the lawn area, which creates an artificial system of large pores that carry moisture and nutrients into the soil.

Aerators are equipped with 3 to 4 inch tines that remove plugs from the soil. While aeration can also be done in the spring, it will bring up weed seeds to the soil surface and create voids for the weeds to germinate.

Establishing a new lawn in September has several advantages. The lawn will have two cool growing seasons before it encounters its first heat stress.

If you are planning to establish a lawn this fall, free, detailed instructions are available at the county PennState Extension Office. Ask for Circular 163 "Turfgrass Establishment." Also available is Circular 39, "Turfgrass Seed and Seed Mixtures.