No advice on what to do, but ask yourself why you think the soil is "lousy" when it supported a magnolia for fifty years. Anything you do (other than the lime - was it needed?) to improve a tree's soil before planting is just going to be history in a year anyway. A tree isn't a tomato plant. Don't work so hard.

It sounds like you are stressing over this enough but the decaying roots of the old tree will play into it far more than the few remaining chips.

What seller of trees will ship a tree, dormant or not, in the fall? All of the reputable nurseries I know of ship dormant trees in the spring.

Here is a link that might be useful: Planting a tree

Thanks all. The lawn around the tree was chemically treated for a long time so on top of being clay and now with wood chips and roots mixed in, it otherwise seemed like dead soil. Guess I'll take my chances and stop trying to amend what's there. It's a Japanese lilac tree. Advice I've read says it can be planted either in spring or fall.

For his zone, fall planting is preferred if the tree can be anchored against winter winds...as it's starting root growth.

If you think clay is bad, try growing fruit trees in sandy soil.

Google hugelkultur. Dig a bigger hole than you need, then drop in large pieces of rotting wood (do you still have some of the magnolia lying around?). That will give the tree roots the support they need in the first few years, as the fungus will envelop the roots and exchange water for sugar. Water of course, after plating the tree, and during the first year.

"The lawn around the tree was chemically treated for a long time so on top of being clay and now with wood chips and roots mixed in, it otherwise seemed like dead soil."

I don't know where people keep getting this idea about dead soil. If heavy amounts of fertilizer were applied for a long period of time, the soil may be unhealthy but it will be far from dead. If the soil were truly dead, then it wouldn't matter if there were wood chips. There wouldn't be any bacteria to tie up nitrogen while decomposing the wood chips.

Did you get a soil test before adding stuff willy nilly?

Why did you cart away all that organic matter? You could have just added nitrogen to feed the bacteria that will decompse it.

Perennial plantings are best made in native soil. The amendments will be gone in short order and then the soil will subside and your crown will be too low. Just plant plants that like the native soil.

if you think the flora in that soil is bad, having whole chunks of safely established flora, such as rotten logs, will provide a starting point for repopulating the soil.

I have read about hugelkultur and will try adding a chunk or two to the planting hole. Thanks. In fact, that's one of the things I did with soil I carted away - used it to cover some logs/branches that I half buried in the back yard. Can't wait to see its progress. To answer an earlier question, part of why I took some of the mess away after the stump grinding was because it was a raised island that was too big and too high. I'll plant grass over the part that I left slightly mounded and leave part (moving the boundary out a bit) as an island for the new tree. No I didn't get a soil test. Suppose I should have. I was eager to get the ground prepped when I had the time and decent weather.

The rotting root structure of an old tree is a great place to plant a new one. The rotting wood holds moisture and provides passages for new roots to get through the clay. I too would have left those wood chips and the small amount of good soil, maybe dig a hole in the center and add some soil to plant the tree in. It'll be fine.

The only thing you added that I would be concerned about without having a test is the lime. Unless you know that the clay in your area is acidic, you don't need lime. Some people lime their lawns routinely without even knowing, so even if your local soils tend to be acidic, if it's been limed it may be higher than the surroundings. Since you added 'a bit' it will probably make no difference, but you might want to look into it before using more lime in your yard.

Mulch that tree well and put a spiral plastic wrap around the trunk to deter winter and spring rabbit gnawing. Good luck!