You can do one or the other, or even both. I'll let the experienced people who've done it before answer this. Personally, I'm going to do both in some areas, and only verticut in other areas (this is due mostly to budget...the front lawn is getting the works, while the back isn't getting aeration this year.)

As for grass seed rates, I'm not sure what type of seed you're planting or where you are. I'm planning to overseed some areas with Kentucky bluegrass, and other areas with both Kentucky bluegrass and turf-type tall fescue. The seeding rates are drastically different for these two due to seed size. I beieve the rule of thumb is 1-3 lbs per 1000 sq ft for new KBG lawns, and more like 9 lbs for new TTTF lawns. For overseeding, depending on how sparse or dense the turf is, you need to cut these rates roughly in half.

One thing to realize, is that most of the "slice seeders" for rental are actually verticutters with seed hoppers, and I've learned from talking with people and also this board that due to major accuracy issues, it's often best to broadcast your seed using a spreader, and then run the verticutter before or after, empty.

I'll let the more experienced members pick up where I left off.

What type of grass is there now? What type are you planning on overseeding with?

Thanks for the replies.
It was hydro-seeded by the builder, I think it's a mixture of both KBG and fescue.
I plan on using Scott's brand full sun, it has a lot of KGB in the mixture.
The lawn gets alot of sun, no tress. Back yard is southern exposure.
Thanks again

There are many oponents to any mechanical disturbance of the soil. I'm not one. I have used plug aeraters, dethatchers and vericutters.

Both aerationa and slit seeding are agressive turf operations. The reason for their use needs to justify the damage that theye will cause.

Aeration is used to reduce compaction and/or reduce thatch build-up. It is not a preventative, it is reactive cure. It can also be used for adding an amendment (like OM) by topdressing into the holes. Seeding is not one of the purposes, but if your lawn needs aeration, overseeding is usually a suggested compliment to help repair the damage. Although a search of youtube will show some videos of grass seed germinating around aeration holes, I've never noticed any advantage to combining aeration and seeding that was an improvement over just overseeding and topdressing.

Slit seeding gives very good results on bare soil or thin lawns. The "slit" seeders available for rental are, as has been said, actually verticuters which cut a furrow/trench into the soil with a 4 toothed blade.

You describe your lawn as fairly thick. If you run a verticutter over an existing lawn, seed will be placed in the furrows you have created, but the existing turf plants that where standing in the furrows will be destroyed or severly injured. What's the gain?

Although this drought and heat has created some dead spots in my lwan and thined out some of the other areas, those thined areas are still fairly thick. I own a "slit" seeder, but I wont be using it on the fairly thick areas and I probably wont use it on the dead areas. I'll be hand raking the dead areas to uncover bare soil, then I'll overseed broadcast seed over the hole lawn (heavier on the bare soil than the rest of the lawn) and topdress the bare and thin areas with peat moss.

I suggest you spot spray with Weed B Gon Max with CG Control to reduce weeds (you can't seed until 2 weeks after applying).
If you feel Overseeding is necessary, start reducing mowing height over the 2 week period after the application of the WBG in increments until the existing grass is about 1-1 1/2".on the day you overseed.

Rake any bare/thin areas to expose the soil. Seed the bare areas and if desired, overseed the hole lawn (the bag should give recommended seed rate for new lawns and for overseeding), lightly topdress the bare and thin areas, apply starter fertilizer and keep moist until germination. Increas volumn but decrease number of waterings. Begin watering regularing after the third mowing. Most importantly: Start using a regular fertilization and lawn care regiment including proper mowing and watering (hervicde and insecticde when called for) to keep a good healthy lawn. Heavier end of season (during early to late fall) fertilization is very important for strong healthy turf. Fertilizing at other times is optional and should be organic.

CRRECTION: other than seeding the dead areas and the very thin areas, I will NOT be overseeding this fall. I've got a pure elite KBG lawn and other than my usual fall fertilization (3# of N and some K) I'll do nothing and let the KBG fill in.

Another thing worth mentioning, is that everyone talks about either rennovation (killing and reseeding) and overseeding as two different things. There is, however, a middleground option...cutting your existing grass short, and then aerating and slicing the heck out of it. This option would be appropriate if you want to keep some of your existing grass to blend with teh new grass to be overseeded. It won't look pretty for a while, of course, and you have to be careful when mixing different grasses due to uniformity issues. but for someone like me, who doesn't demand an absolute showstopper, but just a healthy, nice, green lawn, it's a good option.