Skip the gypsum unless your clay is sodic. Gypsum doesn't help most clay soil.

Check the pH of the mushroom compost and of your soil before deciding to use it. Soils in arid and semi arid areas are often high pH and mushroom compost can be high pH, also.

I like the idea of flipping the grass and building on top.
it's a source of nutrient. why people strip or kill the grass first makes no sense to me.

have you considered raised beds at all?

then you need worry little about your current soil. as i have heard most of us gardeners have clay soils that will benefit from the use of gypsum along with organic material, but you can test you clay to determine that, and if you go for raised beds and throw a bit of not expensive to buy gypsum down and it doesn't work it won't hurt.

anyhow have a look at the pic's on our site there may be some ideas there for you?

len

Here is a link that might be useful: len's garden page

I am interested in raised beds. I am doing so much reading that I am getting crazy about how exactly to build one. My DH says I need step by step directions for things, and he is so right.

Len-I looked at your link. In essence, all I need to do is put down a layer of gypsum, then organic material, newspapers then soil. Can the OM be compost, like leaf compost or homemade? Once I have the soil down, just go ahead and plant?

Anybody else with ideas or recommendations? I would love to hear them.

What I've done over my silty clay soil. 1/4" cardboard, 4" of horse manure, 1" of newspaper, 2" of horse manure, 2" of grass clippings, 2" of soil/compost mix. This is for a bed to planted next spring.

I'll likely fork or till before planting.

I have clay soil. Adding organic matter or compost to any soil is helpful. And it will do wonders for clay. Clay is hard as rock when dry and I've actually had to work it with a pick axe. Then when it is wet, you can sculpt with it. The best time to work clay soil, at least ours here in the Southeastern USA, is to work it maybe 3 days after a good rain, when it is like chocolate cake, it shovels so easily.
I like to flip the grass over too. If that is too hard, perhaps for an older person (me) or someone who just wants to skip that step, then just layer cardboard or newspaper over the grass and OM and plant. It really is easy doing the layering and the raised bed. If one layers big chunks of OM over thick layers of cardboard, one really needs to wait several months before planting. If one builds a 12 inch raised bed with leaf mold and compost and smaller consistency OM, over newspaper (for example) then one can plant into it immediately.

Just an FYI...

Mother Earth News has a great article on ways to make no dig garden beds.

Have you thought about making a lasagna bed? I think it would draw worms to your clay soil and really alter the top of the bed. There are some links around if you are interested; let me know if you can't find it.

Gina

I started a lasagna bed yesterday. Going to plant in it next month. Started small, but if I like how it works, I will make another one for spring planting.

Lisa, if your clay soil right now is wet enough to squeeze water out of it it is too wet to amend even with lots of organic matter. You need to find out why it is that wet and if there is anything you can do to drain it, unless you just had a heavy rainstorm.
You may get some help building raised beds on what you have.

I determined that the clay was wet b/c of too much watering. Our lawn looks the best it has in 4 years. When I dig down, not after a rain storm or watering day, it is not wet. I am still going to go the raised bed route in some areas.

The lasagna bed I made will help when I plant there. I can't wait to see results!!