For over-seeding your typical lawn in SW Michigan, I recommend Scotts Premium Kentucky Bluegrass blend. If you cannot find a pure KBG blend, then KBG with a little fine fescue and perennial rye should work well for you. Equally or more important than choice of seed, cultural practices affect the performance of any lawn. Mow it at 3 to 4 inches, removing only 1/3 or less of the grass blade. Water your lawn when it shows signs of drought stress. Fertilize now and again November 15. Use a pre-emergent crabgrass preventer in the Spring. Use only organic fertilizers in the heat of summer. Allow your lawn to grow long. Water deeply but infrequently. For best over-seeding results, rent a core aerator machine and run it over your lawn a couple times before dropping seed. Good luck in over-seeding your Michigan lawn.

billhill, thanks for the input. I do mow at 3", and water about weekly for at least an hour or so, it just didn't seem to be doing the lawn justice. Like I said, I'm not sure what the lawn is composed of, so maybe it isn't KBG, or maybe the weather is just against me this year. I haven't had to mow in 3+ weeks (because it hasn't grown in 3+ weeks). I will try out the aerator along with your other recommendations. Thanks!

That lawn likely went dormant, and is in trouble, because of fertilizer starvation.

Please tell me when, this year, each of your three fertilizer applications went down.

One in the spring?
An organic, like Milorganite, in June?
An organic, like Milorganite, in August?

Any of these get skipped?

What about last fall's two big-first-number fertilizer applications? Either of those get skipped?

What about the prior owner? Any of his fertilizer apps get skipped?

Yes, I am assuming the lawn is dormant (~2500 sq. ft), but it looks like the rest of the neighborhood, so I didn't think it was in too much trouble. Two fertilizers went down this year. The first was in the spring and the second in late June or early July. I think the spring was a Scotts Stage 1, and the second was a weed preventer + fertilizer (though probably a little late to stop the weeds). In between, I put some gypsum down in an attempt to help loosen the soil. Last year we had TruGreen service the lawn (carried over from the previous owners), so I believe it was regularly fertilized last year (though it still went mostly dormant in Jul/Aug 07).

I'm thinking of core aerating and overseeding with Kentucky blue grass, plenty of water, then a fall fertilizer in a week or two. I also figured I should have the soil tested before any of that. Thoughts?

One of my (newbie) thoughts about the shallow roots was the hard soil. I planted a tree earlier this year and had to use a pick ax to dig the hole, as jumping on a shovel didn't accomplish much of anything. The top 3-4 inches of soil was/is hard as a rock (yet there were very few rocks actually in it). Below that top hard layer, it is "normal" density. That was why I tried the gypsum. I assumed the compact soil had something to do with the shallow roots (If brute force and a shovel has trouble, why wouldn't grass roots?). I assume the core aeration will help. Anything else?

For the watering, I put up an oscillating sprinkler and leave it on for over an hour. How long/how much water is considered "deep" watering? I suppose I should set out a coffee can next time and measure it.

I will start mulching the clippings. I was concerned that would build up thatch, but with a little recent reading, it turns out to be a myth.

Yes, mulch mow and try to use organinc fertilizers. These will reduce the thatch layer. The more organic material in the soil and thatch layer will promote more of the micro organism population. Those are the ones who do all the dirty work and eat away at the thatch layer. To dramaticly increase that population, top dress with 1/4" 1/2" of compost, or spray a compost tea on the lawn. Your lawn will be happy.

If you are going to overseed why not just go the extra step and kill the grass for a full rennovation and have an awesome KBG blend lawn.

Here's the Blend I used based on the national turfgrass reports for southeast Michigan:
Moonlight, Bedazzled and Blue Velvet

Bought from williams lawn seed.

Here's a thread with some pics of my yard in Plymouth MI.
http://forums2.gardenweb.com/forums/load/lawns/msg0911595520648.html

I'll try to get some updated photos up this month, my lawn is recovering a tiny bit from the August drought :)