That's where a community garden comes in. Community gardens are public or donated plots of land where a whole community can come together and plant flowers and vegetables. They bring green plants and fresh fruits and vegetables into urban areas, and often they give kids their first look at how their food is grown. There's an article here about the effects of community gardening in Pittsburgh.
Interested in finding a community garden, or starting one in your neighborhood? The American Community Gardening Association is a great source of information. If you're interested in organizing one of these gardens, it could be a great service to your community.
(Image credit: American Community Gardening Association)