Question
link below the question is a photo of the spot I'm working on.
I want to add a raised flower bed around a tree....before filling in my prefered soil, would I need to eliminate the grass first?  that would be difficult because the tree roots so close to the surface.
photo:  http://img.photobucket.com/albums/v408/unstresst/yarddd1.jpg

Answer
Hi Mike, I'd prefer to kill out the grass before building the flower bed.  Most grasses would probably not survive a deep layer of soil added on top but some will, so I'd spray them with glyphosate.  It is not absorbed through roots, so it will not harm your tree or your new plants. Spray it, wait 1 day and cover.
Another option, if you don't want to spray and aren't in a hurry, would be tarp the area with black plastic.  Most grasses will not survive a month without light.  Then remove the plastic and add the soil immediately.  Jim