As you can see from the photo (which comes courtesy of Windowfarms on Flickr, by the way), a window farm is a hydroponic window garden made from old plastic water bottles, or other various materials.
Here’s an excerpt from the Window Farms site that helps explain what it’s all about.
Researchers have argued that to grow some of his own food is the most effective action an individual can take for environment, not only because of the food industry’s heavy carbon footprint but also because participating in agricultural production cultivates a valuable skill set around sustainability issues.
Many neighborhoods (particularly low income ones) in cities aroun the world are considered food deserts, meaning little fresh food is easily accessible. Residents tend to consume processed, packaged, and canned food having depleated nutrients.
Few other projects provide opportunities for such direct personal involvement, make this productive use of existing construction, or so directly target urban dwellers estranged from agricultural issues.
Inner city dwellers can grow their own food in their apartment or office windows throughout the year by means of these elegant, inexpensive, vertical, hydroponic vegetable gardens made from recycled materials or items available at the local hardware store. The first system produced 25 plants and a salad a week in mid winter in a dimly lit 4’ x 6’ NYC window.
The site has a How To section with plans, if you want to grow your own window farm.
Here’s one of their YouTube videos: