Growing salads, fruits and herbs vertically not only allows urban dwellers to grow food in small spaces, but follows the permaculture principles of stacking, using renewable resources and making the most of the edge.
Permaculture plant guilds combine three or more plants to mirror an ecosystem — producing food, building soil health, and providing food for pollinators. To learn more permaculture principles, check out out Tierra: Online course.
Permaculture Principles for Practical Gardeners and Farmers -
Finally, a permaculture article that doesn't read like a religion. These 9 permaculture principles are based on the concept of mimicking Nature. Suggestions and examples are given, so you can implement them in your own garden or farm. Just the science; no politics.