plese check out his website:http://www.bund-berlin.de/extras/baumscheiben/scheibe.php
it has over 40 pictures of tree pit gardens
its from the environmental organisation b.u.n.d. and one thing they do is arranging this contest who-has-the-prettiest-tree-pit-garden (you can win a 150 euros worth of plants), even though it it not legal and in some neighbourhood your efforts might be destroyed by city "gardeners". 2006 is i think the third year of the contest.
also, check pressemitteilungen on gruentmit http://www.farank.com/gruentmit/unterseiten/pressestimmen.htm
there s newspaper articles as pdf files (all in german, sorry...) that have some pretty nice pictures of frank and his tree pit gardens.
and the winner of the baumscheiben award 2006 is....