The idea is that becasue there is a trend for people to buy "organic" and pesticide-free. herbicide-free, etc food and they are willing to pay for it; then if an enterprising person bought a small are of land in or near a city, then that person could charge people for renting a small area of land and tools on which to grow their own food.
You could own an abandoned lot or three, put a small shed with rakes, tilers, etc and in exchange for a fee you'd give them a key to the shed and an area of your land.
Environmentalist city people would get the joy of growing their own food near where they live.
The money making part could work similar to the way that gym memberships do. (Upfront payment, who cares if they grow anything.)
One major problem would be being allowed to have a commercial farm in residential or commercial zones. Getting a pass on the zoning laws would likely be a hassle.
Its a rough idea, but its the execution that matters in business not the idea.