Usually big cities dont have infraestructure to have gardens or soil in where to have a little farm. Also, the fruits and vegetables that are sold in supermarkets or so might not be the most healthy products. There's a big BIO trend these days.
So, the idea is to have a public farm where the user could rent farming/gardening modules (1m2) and grow their own crops. Berliner Sparkasse customers could rent these modules for a cheaper price! By this, we would also create a control of who gets into the space reserved for farming.
This concept could be also applyed to floating farming, where the modules are placed on flaoting structure on the river or lakes in Berlin.