Question
I live in the Kansas City area. My lawn is only a year old, it was sodded last August. This year it is very patchy and needs to be overseeded. What are your suggestions for overseeding a lawn.

Answer
Good evening Mike:
The optimum time to seed cool-season turfgrasses is between Aug. 15 and Sept. 1 in your area.
Mow the area to 1.5 inches to reduce competition from established grasses.
Apply a starter fertilizer (high in phosphorus) over the entire lawn at  a rate of 1.5 lbs per 1000 square feet.

For successful overseeding, it is critical that seeds be placed into contact with the soil, whether seeding into live or dead turf. Seeds scattered on top of live or dead turf rarely produce a decent stand of turf. Several ways exist to place seed in contact with soil.
To open the soil for seeding in large areas, use gas-powered vertical mowers,
slicers, core aerifiers, spikers, or slit-seeders. All of these tools should be available at most rental agencies.

Core aerifiers open soil by inserting hollow tines into the ground and removing
plugs of soil. When using a core aerifier for overseeding, it is important that at least 20 plugs per square foot be extracted. After broadcast seeding, allow
the plugs to dry and use a drag (a piece of chain link fencing works well) to work seeds into the soil and crumble the plugs.

Another method you might consider is a slit-seeder. These are recommended when you presently do not have a thatch or compaction problem.
Slit-seeders (mechanical overseeders) are considered to be the most convenient
method of placing seeds in contact with soil. These machines combine a
vertical mower with a seed spreader. They open the soil with a vertical mower
mechanism, and then seeds are metered at a predetermined rate from a holding
hopper through feeder tubes and dropped into the slits made by the vertical mower. Machines often have a roller that firms the soil after seeding. Slit seed the area twice; the second pass should be at a 45?angle to the first pass.

To renovate successfully, adequate water must be available from seeding through germination. Water the newly-seeded area three to four times daily. Light, frequent irrigation is the rule. Try not to allow newly overseeded areas to dry once watering has commenced. Maintain a constantly moist seedbed. As newly germinated seedlings begin growth, decrease watering frequency and increase the duration to encourage rooting.

Mow frequently to limit the competition from the established turf. Mow at 1.5  to 2 inches until new seedlings have been cut at least two times. After that, raise the mowing height in 1/2 inch intervals over the next three weeks until a normal mowing height of 2.5 to 3.5 inches is reached.
In late November apply a winterizer fertilizer to create good root growth for next year.

Some web sites that may be of interest to you are:

Missouri Cool Season Grasses Lawn Renovation:
http://muextension.missouri.edu/explore/agguides/hort/g06700.htm

Missouri Lawn Calendar:
http://muextension.missouri.edu/explore/agguides/hort/g06705.htm

Have a good lawn!
Floyd McMahon