In our town, we have a little community centre located in one of the urban neighbourhoods. The purpose of this centre is to create a place for community projects, which the people from around the neighbourhood come up with. So far its efforts arent that visible and they are mainly concentrating on the very poor and homeless, which is great of course, but these people are on average older and missing that spark, that is needed in order to come up with something new.
So my idea is this. There is a formerly homeless guy in this centre, whose responsibility is to watch over it after everybody has gone home. Also there is a open space with grass and a tree inside the building (dunno if you can imagine this, but its like a small garden surrounded by the building from all sides). So why not turn this area into a real garden, which anybody could take care of, but primarily it would be intended for the caretaker guy.
This way he would not have to spend so much money on at least the vegetables and whoever would want to do something around the garden (just for fun or for anything else) including this guy, could do so. Hell I should even ask my friends who are studying architecture of gardens to make up some plans for this.
So far its only an idea and it will take a lot of work and discussions with the centre, as I dont have any real means to make them do anything, apart from my rhetorics :)