We have hardly mentioned rooftop/above-ground gardening since EDN 30, but activity has continued in this area both at ECHO and a few other locations. Last summer a large garden was grown on the roof of the main prison in St. Petersburg, Russia, and 18 other rooftops there had gardens ranging from small to substantial. We are exchanging weekly e-mail messages with a group in Moscow that expects to begin work this summer.
I [MLP] recently visited Doug VanHaitsma and his national colleagues in El Salvador to evaluate the potential of urban gardening in a low-income part of San Salvador. After seeing slides of all the methods mentioned in EDN as well as tire gardens, everyone chose the tire gardens as most relevant for their needs. I share their enthusiasm. (The method seems to have been developed or at least promoted by a United Nations project).
Construction is simple and elegant. Lay a tire flat on the ground. Note that the top rim is a mirror image of the bottom rim. With a knife or machete, cut off the top rim. Place a piece of plastic inside the tire on the bottom rim, large enough so that an inch or two of plastic stands up along the walls of the tire. Now turn the top rim that has been cut off upside down. It fits like a lock on the bottom rim, holding the plastic firmly in place.
Any suitable soil, compost or potting mix can be used to fill the tire. You will need to judge when/if fertilizer is needed, based on what you use for a medium and how plants are growing. At ECHO we sometimes place an empty flower pot or a PVC pipe in the center so that we can see how much (if any) water is standing in the bottom and so judge when to water.
We usually incorporate something with a lot of air space into the medium. This helps extend the growing medium that is usually in short supply, and makes the garden much lighter. At ECHO we use cola cans with holes cut into the sides so roots can penetrate the can. In El Salvador coconut husks, which are everywhere, were broken up and incorporated. In Mexico City, Dan used a layer of alfalfa hay to provide initial aeration plus subsequent nutrients.