Question
Zone 3. Our grass is very thin and in some places bare so we are going to try seeding it. The only part of the process I am unsure of is watering after the seeds have germinated. How much water do the little sprouts require and when can we start the less frequent deep watering to ensure deep roots? At what point should we fertilize?

Answer
Good afternoon Natalie:
Begin your overseeding and repair from the middle of August up to the last week in September. If you do it now it will be very stressful on the new seedlings going into the heat of summer. Cool season grasses  require cool temperatures to germinate and grow properly.
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.
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 which would seem to be right for your lawn.
Slit-seeders (mechanical overseeders that can be rented ) 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. Try not to allow newly overseeded areas to dry once watering has commenced. Maintain a constantly moist seedbed with frequent watering of short duration. As newly germinated seedlings begin growth, decrease watering frequency and increase the duration to encourage rooting.

When cutting your lawn, it is advisable to cut at a height of 2 ?to 3 inches.
Cut more frequently and remove approximately 1/3 of the grass blades at a mowing.
When grass is cut too short and more than 1/3 blade height at a time, the cut grass does not break down properly and contributes to a weedy and thatch filled lawn. The only time you would need to bag your clipping is if you are removing more than ?of the blade height. If you do bag your clippings, and they do not have herbicides on them, use the bagged clippings along with shredded leaves this fall for  composting.

Early fall (September 1-15) is a key time for fertilizing lawns in your area. The schedule below outlines when to apply based on how many applications are to be made annually and desired lawn quality. Use controlled-release nitrogen fertilizers in May and September and a fast-release source in late fall. Consider Mother's Day, Labor Day and Halloween as reminders or favorable times to fertilize lawns.
If you desire a moderate quality lawn I would suggest you apply two applications. One in early May and one in early September.
If you desire a moderate to high quality lawn I would suggest you apply three applications. One in early May, one in early September and one in late October or early November using a winterizer fertilizer.
A good winterizer fertilizer would be a 24-3-12.

Avoid fertilizing in midsummer when the lawn is growing slowly. (Yellowing or fading grass color and loss of vitality indicate the lawn may need a boost.) If you live in an area with alkaline soil, using a fertilizer that contains extra iron will help keep your lawn green.

A web site that you may find interesting is "Repairing a damaged lawn":
http://www.american-lawns.com/problems/repair.html

Have a good lawn!
Floyd McMahon