I'm on my 3rd set of sugar maples and I'm afraid these ones won't last as well, so I need some help.

Back in Fall 2002, the first set was planted by a local nursery. By the following year, it was clear that 2 of them were not going to make it. The nursery fertilized the trees and asked to wait another year to see if they come back. No luck. In 2004, the trees were dead, so they were replaced.

Later in Fall 2005, it was again clear that these trees were not going to make it, so I asked that they be replaced again.

Now, the trees are still not looking good (light green leaves with brown edges), so I'm wondering what needs to be done (I don't want them to die!).

A few more bits of info:

1) I'd be surprised if lack of water is the issue. I watered the trees extensively after they were planted at least once every 2 days or so, but sometimes every day. I did this for about 3-4 weeks. In the spring/summer, I've also been watering heavily twice a week (i.e. I keep the hose around each tree for 10-15 minutes with a heavy shower). These trees also get water from the lawn sprinklers (twice a week). And, with all the rainfall we've had, I can't imagine they are not getting enough water.

2) I had 4 other trees (1 other sugar maple) planted at the same time as the original trees, and all are thriving.

3) The soil is poor (in my opinion). Clay with relatively poor drainage. I don't know if the nursery amended the soil at all. Could this be a case of "overwatering", or root rot?

4) I fertilize the lawn with the typical Scotts fertilizers. I have spread "Super Phosphate" around the drip edge of the trees to help with root growth.

5) The nursery planted the trees level with the ground (not higher as I've seen other trees planted). Could this be contributing?

Any help would be appreciated...