The blog is run by two guys, Eric and Sean who are trying to activate public space - attempting to engage with urban environments- in Toronto, Canada. Basically they use the old advertisement posters and create small pockets where they plant seeds. Some call it a little guerrila gardening but I see this more as an 'Urban Hack' in its ability to jam an urban system and provoke reaction.
See the pictures below taken in Toronto by Sean.
I think the idea is simply great...all the cities would look much better with more flowers and planst( and less ugly posters!)