For seeding or overseeding a lawn, September has long been considered the best month. This is true when cool season grasses such as bluegrass and fescue are being used. At this time of year, soil is usually not excessively wet and works well but fall rains are soon to come to make the watering, which is necessary for good seed germination, less of a chore. In fall some of the problem weeds such as crabgrass do not germinate and crowd out young, weak seedlings as they do in spring.
In preparing for seeding a lawn, one of the first steps to take is the elimination of existing perennial weeds. This may mean the application of a herbicide such as glyphosate (Roundup) to kill problem perennial grasses such as bermuda as well as most broad-leaved weeds. It will take at least two weeks after spraying before the area can be worked, but there will still be time to prepare and seed the area. If the fertility levels of the lawn are not known, a soil test would be helpful, particularly for the establishment of a new lawn.
If weather conditions have been dry, it is a good idea to water the area to be seeded several days before preparing the area. A slightly moist soil will form a better seed bed. After the soil has been moistened and weeds are yellow and dying, the soil should be tilled to aerate, break up compaction, and incorporate lime and fertilizer into the soil. If the area to be seeded has a layer of dead grass thatch, this layer should either be removed or tilled deeply into the soil. If the soil is low in organic matter, the incorporation of compost, aged manure, peat moss or other similar materials can speed establishment and growth.
The pH of the soil is best determined by a soil test and should be adjusted so that the acidity of the soil is between pH 6.0 and 6.5 for best grass growth. Lime is used to raise the soil pH and sulphur is added to lower the pH. Ground limestone is usually the type of lime used for raising the lawn pH. It is slow reacting and should be mixed into the soil before seeding. If it must be applied to an existing lawn, it will be most effective if it is worked into the soil after it has been spread on the surface by using specialized lawn equipment such as a vertical mower or a core aerifier.
If it is not possible to get a soil tested in time, a few general concepts might be applied. If the soil has been limed in the past but not for at least two years, apply about 25 pounds of ground limestone per 1,000 square feet of area. Phosphorous will also most likely be needed. Add it to the soil at 5 to 7 pounds of treble super-phosphate (0-46-0) per 1000 square feet. If only normal super-phosphate is available, use it at about 10 to 15 pounds per 1000 square feet. Since phosphorous and lime are not very mobile in the soil, till them in to at least 4 to 6 inches deep. To supply a little nitrogen and potassium to serve as a starter, in the final preparation of the lawn for seeding, add a complete fertilizer such as a 10-10-10 at a rate of about 10 pounds per 1000 square feet and work it into the top inch of soil. Nitrogen and potassium are very mobile, so more can be added later as a lawn fertilizer after the grass has germinated and reached about first mowing height.
The seed bed should be fairly fine and not full of large clumps. Make it as level as possible. High areas may dry too fast and seeds may be killed during germination. Low spots may remain too wet, particularly if frequent rains develop during the germination period, which would again lead to reduced germination.
There are many good grass varieties. The turf-type fescue varieties are becoming very popular and have good durability and disease resistance. Once the area is ready, bluegrass should be spread at about 2 to 3 pounds per 1000 square feet and fescue will require 6 – 8 pounds per 1000 square feet. After seeding, aged straw or hay that is free of seed can be used for a good mulch. Do not spread it too thickly. One square bale should be enough to cover 1000 square feet. There is no need to remove the mulch after the grass has germinated.
Keep the surface of the soil moist during the germination process. With good care, fescue varieties should germinate in about a week to 10 days and bluegrass in 2 weeks or a little more. Once germination is complete, reduce watering to about once a week or enough so that with natural rainfall it will provide one inch of water per week.