Oren wrote:

+1 on using gypsum. Use a coring aerator that removes the 2" plugs.
Scatter the gypsum and water the area. The gypsum helps break down
the clay so water can penetrate the soil - in my experience.

Coring also allows plenty of oxygen into the soil.

You guys (particularly you Oren) are full of so much shit on this topic
it's beyond belief.

Your ideas especially about oxygen are pulled straight out of your ass.

You have absolutely no idea what the gas permeability is of soil,
especially given all the different conditions you're going to encounter.

This guy (Bob) lives in what is becoming a desert (California, Long
Beach). His soil will be very dry and porous and this is not an issue
of getting more atmospheric gas in contact with roots.

The accepted treatment for patchy lawns growing in clay is to top-dress
frequently with top soil and throw in grass seed and fertilizer.

AND LOTS OF WATER - something the OP will not be able to do.

There are con artists that troll neighborhoods in the spring with
aerators they rent from Home Despot. I garantee you they do not bring
top soil or gypsum with them to rake into the holes as part of their con
jobs. And they set their plugs to barely reach 1.5 or 2" so they don't
cut any in-ground infrastructure (irrigation lines, telephone or RG-6
coax cable).

The OP has primarily a water problem, and either too much or too little
shade for his lawn to thrive. Throwing down a good amount of fertilizer
and water can do amazing things for a lawn, even in clay.

I live in the middle of the great lakes - this is clay central. My own
property is in an area that was once dug up decades ago for clay to make
bricks. I have never once aerated my lawn in 15 years of ownership. My
grass does very well in the areas I bother to take care of it.

And here I will give you one expert who is basically saying that adding
gypsum after the fact to an established lawn is full of shit:

http://web.extension.illinois.edu/as...AskSiteI D=34

==============
We often get this question about how to improve the structure of a soil
after plants or in your case a lawn has been installed. It is not easy
and often there is not a very efficient way of doing this because you
don't want to start over. Ideally we like to see soil improvement done
before planting and the best way is to incorporate a lot of organic
matter into the soil.

Many people think that gypsum is the magic cure for clay soils. While
gypsum is often suggested to help loosen up clay soil by getting between
the particles and helping to floculate or open up the soil for better
air and ater movement it often takes time and if a plant is there again
it can't be incorporated the way it should be.

The only way I think you can help a tight clay soil under sod is to do
vigorous core cultivation. This means using a machine that puts holes
into the ground that are at least 4 inches deep and about 1/2 to 3/4
inch in diameter with the holes being no more than 2 inches apart.

After that you can topdress with good soil that is worked into the holes
and allows air and water to start moving down and supporting good root
structure. Gypsum could be added but it isn't going to do the job as
well as if it were to be fully incorporated. Doing this coring regularly
will eventually start to "replace" the soil one core at a time allowing
a better soil environment for root development.
================

FOUR inches deep. Take note of that. Half inch to 3/4 diam, NO MORE
THAN 2 INCHES APART.

Your lawn is going to look like swiss cheese after that.

If you're going to do that, you might as well rototill the whole thing,
and ADD SAND. Playground or brick sand. That will probably work better
(and cheaper) than gypsum.

"Doing this coring regularly ..."

Who the hell wants to break their back doing that "regularly" ?

Either just top-dress once or twice a year, or rototill the whole dam
lawn, truck a good amount of the clay away and replace with some good
black earth and load it with some good grass seed and fertilize.

But again, maybe you're just wasting your time since you're in the
middle of a drought and who knows when it will end. Probably not a good
time (or a good decade) to try to do any lawn rehabilitation in
California.