Tree Pit Garden

In Vienna it is possible to become a "tree patron" which means that you are officially allowed to transform a tree pit in your own small garden - you just have to apply at the competent area renewal office. I think this is a very good idea, the city gets more green without spending money and hobby gardeners get a "playground". The only things I'm worried about are litter and dog poop... The tree pit garden in this photo is located in a quiet street close to my place, it is very well kept and seems to be (still?) very clean.