Janie,

Go look through the Dirt Doctor site. He is here in Texas but he gets questions from all over the place, and I think you'll find some useful information. One of the things that has come to light lately is that if trees are planted too deep in the ground, so the butt swell is under dirt instead of showing, that the tree is already compromised. You can wash or brush dirt away from that area and see a significant difference. (Nurseries tend to dump more dirt on top of the roots when trees are in pots if it looks like the trees don't have enough roots. But you're better off shaking off all of that pot dirt and treating them like bare root trees).

There are good natural fertilizers, there is the sick tree treatment, a mix of fertilizer and aeration and foliar feeding. I had a redbud that was looking awful a couple of years after I planted it, but I did the sick tree treatment and it came back like gangbusters.

You need some sun for planting other stuff, but this is getting it the hard way, losing trees to disease. Maybe a good arborist can help you select which ones to rescue and which to take out.

SRS