I’d like to plant a vegetable garden on my roof. It will be in a feed trough about 8 feet long, and 2 feet wide and deep. I’m wondering what I can add to lessen the weight of the container (so it won’t just be filled with potting soil and compost). Also, any recommendations for which vegetables to grow would be great–things which are fairly easy and don’t have enormous roots!
To lighten the load of your container, a lightweight organic material like hazelnut shells might make a good bottom layer. You could use perlite, but that may actually be heavier than the nut shells. Here is information about sources of hazelnut shells:
Oregon Hazelnuts (a website of hazelnut growers) (lists several sources)
A Washington State source, often found at local farmers’ markets, is Holmquist Hazelnuts.
The book The Edible Container Garden: Growing Fresh Food in Small Spaces by Michael Guerra (Simon & Schuster, 2000) has a section on rooftop containers, and recommends (after you’ve consulted a structural engineer) using lightweight, well-draining compost, and setting your container(s) on timbers to help with drainage. According to the book, the best candidates for containers are potatoes, chard, lettuce, radishes, shallots, bush tomatoes, eggplant, zucchini, squash, dwarf carrots, dwarf beets, mustard and Asian greens, and runner beans. More difficult are cauliflower, cabbage, Brussels sprouts, kale, parsnips and other deep-rooted vegetables.
The following links may be of interest:
University of Maryland Cooperative Extension
Vegetated Roofs from Oregon State University Extension
Article about the Reading International Roof Garden (Britain) from The Guardian by Emma Cooper (and another article by this author in Permaculture Magazine #53).