How to weed tree wells?

 Hi everyone,
I have a question for the experts here. I recently moved to a new
house(about 5 months now). What is a fast way to weed the grass/weeds
growing from the tree well. Basically, the mulch/soil around my tree
has weeds or unsightly grass growing in it. I tried my weed trimmer but
that just scatters the mulch and dirt all over the place. I tried
picking them with my hands to get it out through the roots, but it is
hard and  scatters the dirt also. I have tried burying the weeds with
more mulch, but it grows through it within a few days. There has got to
be a better, efficient way to do this? Any suggestions or pics on how
to do this? I've noticed other houses where the tree wells don't have
any grass/weeds growing from it. They must know some grooming
techniques, but i never see them out doing yard work. Thanks for all
the help!

 Selective use of roundup. Landscape felt under the mulch would help too.

 But wouldn't Roundup kill the soil also? I heard it can kill anything.
What do u mean by landscape felt? BTW, here are the pics of my tree
wells. The first 2 pics are the tree wells and the last pic is the
shrubs and bushes in front of my house.  Thanks.

http://i56.photobucket.com/albums/g187/zcarenow/Picture001.jpg
http://i56.photobucket.com/albums/g187/zcarenow/Picture002.jpg
http://i56.photobucket.com/albums/g187/zcarenow/Picture003.jpg


Mike Robinson wrote:

 
zcarenow@yahoo.com wrote:

No.  RoundUp works by entering the plant through the foliage, not the
soil.  RoundUp starts to degrade as soon as it touches the soil.  It
does not contaminate the soil or make the soil infertile.

 Roundup wont kill the soil, but small amounts will kill the grass and
shouldn't affect the tree.