smallaxe, you know by now that I am one of the guys that continue to state that aerating and over-seeding does improve a lawn. I also mean this from a couple of different perspectives.
I am going to go over board here so that I am sure that we have an understanding of one another!
First, I believe that annual aerating will improve a lawn that is being well cared for in the other aspects of lawn care by reducing thatch buildup (yes, REAL thatch, by definition) and by reducing compaction allowing new and healthy root growth and spread as well as open the soil to encourage nutrients to more easily reach the root zone. I have also seen lawns improve from this in just one season where it hadn't been done in years, prior. Again also considering that othert aspects of proper lawn care are being done (proper mowing, fertilizing...).
I have also experienced quick improvement of lawns by aerating and over-seeding. First, lawns that may be just a little thin in areas by this method. But also, including this year, rather large areas of lawn that were damaged heavily by heat/drought or bug damage. Most lawns that I aerate and over-seed is just a single pass or two, if requested, and over-seed with 3 lbs per 1000k of a 50/50 blue/rye mix (until mid Oct when I gradually shift to more rye). Second, lawns that may be more heavily damaged I may aerate the area 2, 3, 4 or more times depending on the area and seed at 4-5 lbs per 1000k.
When you go over an area where there is no grass or it is all dead anyway, 3 or 4 times, it chews the area up pretty well. It is almost like a mini tilling job. Just a few inches deep is the difference though. Plenty for new seed. You have holes, lots of chewed up soil and plugs that will be breaking down over the next couple of weeks. In the regular lawn or the thin lawn, you have the holes and plugs (again that will be breaking down over the next couple of weeks) of course.
I fully understand what you mean by "doll hair effect" and I will grant you that is exactly what you get at first
. But if you will just be patient and watch, you will begin to see grass sprouting up in between where the holes are too. As the plugs break down the seed in those areas are now under a little soil and too have some opportunity to germinate as well. And because as you know we are all fertilizing our customers lawns, probably way more than they could ever really need, there is plenty of nutrients to encourage our new grass to root well and spread!
You seem to be a man with plenty of understanding and experience so I can only guess that you haven't really given a job like this the time to see results, used too little seed, no fert, bad time of year, I can only guess. As I just stated in another thread yesterday, God created grass to produce seed to just drop off right there with zero prepping of a seed bed and it has existed just fine for thousands of years.
I will also grant you that this isn't always the best method, especially a large area that needs completely re-done. But I will say again, that aerating and over-seeding is a quick, easy and fairly inexpensive
way to quickly improve
a lawn. Especially if you compare it to other much more labor intensive, which also means expensive methods.
Some of this, you have said in different words and we are in agreement as far as the difference between renovating
. So maybe, we (myself included), need to watch how we use those words. They are not interchangeable of course.
So, to answer your question! You aerate and over-seed every year, relying on the holes and break down of plugs to repeatedly produce more healthy grass plants that will spread until every square inch of lawn is completely filled!
Then, you just aerate yearly to keep that nice thick lawn healthy with minimal thatch.
I know this. I love aerating and love what it does for lawns. I do alot of it.