Question
I plan on renting a vertical dethatcher with a bagger and an aerator for my lawn this weekend.  I live in Indianapolis and would like to overseed after I do this.  My question is:  Is it ok to dethatch and aerate at the same time?  Also, how deep should I set the blades on the dethatcher?

Thanks,
Jim  

Answer
Dethatching and aeration accomplishes different tasks.

The dethatcher's primary function is to slice through the thatch making it possible for water, nutrients and oxygen to reach the root zone, and for carbondioxide to escape. Some damage to turf is anticipated but if done at the right time (and early fall in indiana is the right time) the lawn should recover.

If you have a thatch problem, set the dept of the knives to penetrate the width of the dept (you can try to dig a core of soil and investigate). Typically you would need to set it atleast 1" or deeper. If you are using the dethatcher to just remove any debris on the surface of the soil and to slice the soil in preparation for seeding, then 1/2" is fine. This is if thatch is not a big problem.

Core aerators pushes hollow tines into the soil and pulls out cores of soil which are deposited on the surface. The core holes will allow oxygen, water, and fertilizer to penetrate to the roots, too, but only where the holes have been made. Therefore, core aerating is recommended even on lawns with moderate thatch. If you have heavy thatch (more than 1/2") then you should use dethatchers. If moderate thatch, you may want to simply forget about the dethatcher and instead run the core aerator over the lawn a few more times. If done in early fall (in Indiana) you really can not make too many holes.

Core aerators are preferred to spike aerators (which only punches holes, but do not remove cores of soil). spike aerators will also punch through thatch (and therefore can be beneficial) but compaction is not aliviated which is one of the prime benefits of core aerators.

you can do both, but you should expect some damage to your lawn as result. Overseeding afterwards is doable. If you have clay soil, I would rake the cores as wet cores tend to mash down and kill the existing grass. If you are going to sow seeds, you will need to water frequently (2-3 times daily) until new grass has germinated/sprouted.

Overseeding after core aerating and/or dethatching is much recommended. I am myself a big fan of core aerators.

Good luck,