Beginner Gardening: Amending soil around a tree (and bushes), 1 by grrrlgeek

grrrlgeek wrote:
We've got clay with no topsoil. The area in front of our townhouse needs work, but there's a linden tree smack dab in the middle, and some shrubs I may or may not remove or move. When the builders planted, they just dug holes the size of root balls and stuck the plants in (as I found when digging around) so the tree and shrubs would probably be happy with a little air and water getting to the roots. The pic shows the area in August 2007 (before all the poor little columbines died :~( The area is surround by asphalt and concrete, so I was thinking I may have to actually remove some dirt to add amendments, or at least relocate it until things sink back down. How close/deeply can I dig around the tree and/or bushes? Are there any amendments in particular I should avoid around them?