I have a river birch that is about 20 feet tall that starting last summer started to have yellowing leaves mid to late summer. The tree came back fine this year but again in the last couple weeks its started to yellow and leaves are falling off. I don't think it's too much or too little water. From what I've read sounds like soil issues. It is a heavy clay area. What additives and what method should I use for the soil?

Ripper,

I'm going with the clay thing and not enough nutrients/water. I have three in my yard and experience the same thing.

I bought a product called a "Ross Root Feeder". It is a metal wand that hooks up to the garden hose and you insert it 6-12 inches deep in the surrounding soil. It holds water soluble fertiler chunks that dissolve as you water. I usually water for about 15 minutes a tree and fertilize every 45 days starting May 1st and ending Sept. 15th.

Run your garden hose to the tree then, turn the water on a slow trickle for a minimum of 8 hours. Do it again in 2 weeks and your tree will be fine.