A shallow or mini-raised bed—just a yard square and 6 inches deep—will allow you to grow herbs and vegetables on a small patio, balcony, or rooftop. (Be sure to check with a structural engineer or contractor to make sure your roof or balcony is strong enough and waterproof.)
A raised bed is a bottomless square or rectangular frame made of planks. Many garden centers sell lightweight raised bed kits. You can also grow crops in a flexible bag planter.
Place landscape fabric under your raised bed to prevent potting mix from sitting directly on the roof or balcony surface. Many raised bed kits include feet and wire-mesh panels to set the bed up from the surface; place the landscape fabric below the mesh.
For balcony and roof-top beds use a lightweight potting mix; look for a soilless mix or lightweight potting mix. Add worm castings or well-rotted compost to the bed once or twice a year to keep the soil fertile.
Here are crops for raised beds 6 inches deep, 8 inches deep, and 12 inches deep:
Crops to grow in a 6-inch deep bed:
- Asian greens—mizuna, mibuna, tatsoi
- Beans–bush beans, climbing pole beans, and runner beans
- Herbs–basil, chives, cilantro, dill, oregano, mint, thyme
- Lettuce and other greens
- Onions, shallots
- Tomatoes—bush, determinate, miniature, tumbling
Crops to grow in an 8-inch deep bed:
- Fava beans
- Florence fennel
- Herbs—rosemary, sage, tarragon, parsley
- Peppers—bell peppers and chiles
- Tomatoes—bush and vining
Crops to grow in a 12-inch deep bed:
- Currants—red, white, and black