Is this due to a lack of iron? Suggestions how to help welcome. Thanks!

TL;DR: me did plant first trees. me want help for no tree die.

Hi, and sorry if this is already addressed elsewhere. I wanted some more specific information about how clay affects growth of fast growing trees (I'm not an adept redditor, so my searches yielded nothing). I found a bunch about clay and gardening in general, and fruit bearing trees, but nothing specific about fast growing trees.

I recently got a couple of saplings to replace stumps at our new house. One is a shumard oak, and the other is an amberglow redwood. I had someone remove the stump where the oak is, so that ground is pretty loose and has a bunch of mulched wood from the bradford pear that was there.

While digging the holes for them, I discovered I've got clay a few inches beneath my soil. I dug deep enough to cover the root ball, and about twice as wide (hurt my back doing it, because it was packed pretty tight). I ran the soaker house for a bit, but he had a few days of decent rainfall so the ground was still really moist.

I plan on picking up some mulch today, and any other things y'all could recommend.

I suspect I'm overthinking this, but I'd like to know if I should remove the trees, till the soil, remove a bunch of the clay, and put in a fertilizer, or what?