@takuan: as far as i know, the guerilla gardening movement has its roots in pot planting - on the balcony of a police station, where it went unnoticed for months :)

i'm no guerilla gardener, but i did it once, together with my sister. there was a guy she liked, and he liked to relax under a tree on the old university campus in vienna and eat bananas.

so we bought a tree (not a banana tree), organized a spade and went to the old campus after midnight. there we dug a hole, planted the tree and decorated it with bananas. sadly, it was march and still snow lying around - not the best time to plant. we knew it wouldn't survive, but it was more of a symbolic action. and yes, he liked it a lot (they're still together for about 4 years now). it also was a great thing riding around in public transport with a tree and a spade - a lot of strangers started to talk with us, how great trees are, and where we got this lovley one :)

a couple of days later the tree was removed, probably by the (city) gardeners, but we expected that.

what we did NOT expect was that they re-plantet it a few days later! sadly, it was ultimatley removed some days after that, probably because the plant died.

i even have pictures of the "incident":
http://wehrlos.strain.at/evil/

another story (if i remember it right, i can't find the link to the story anymore): guerilla gardening is not very popular in vienna, because it's already quite a green city. despite that, two undergrads (not us!) tried it, but with the blessings of the MA42 (the viennese garden magistrate). after some time, it was destroyed (the suspects were some teenagers who always hung out in this park). the girls didn't blame them, but asked them to help repair it, and it worked great - the kids really liked it!

i guess, with serif fonts they would be steam punk robots.