Although raised beds work as well in large spaces, gardening in a singe raised bed is a productive small-space experience. A raised bed can retain extra warmth, lessen weeding, and let you use previously awkward spaces for additional gardening. Usually somewhere between 4-18 inches high, a raised bed can also bring great relief to that chronic spring-to-fall crick in your back.
Use landscape cloth to prepare your bed for warmth, soil retention and weed control. Staple a layer of cloth at the bottom of your raised bed. Its dark color absorbs warmth, and, especially if you plan to situate your raised bed on a non-soil surface (like a patio or paved surface), the cloth liner will prevent soil runoff from the bottom of the bed. Your liner also prevents weed seeds from forcing their way into your garden soil.
Add soil to within an inch of the top of your bed, turning in peat moss, compost, and sand as needed to assure good water drainage. Soil enrichments are especially important in deep raised beds because plants may not have access to soil nutrients under the bed.
Choose plants that will flourish in the depth of soil your raised bed provides. A 4-inch-deep bed will provide adequate root-space for salad greens, annual herbs and most annual flowers. For root-crops, long-season vegetables (like tomatoes, eggplant and peppers), and perennial flowers, allow a depth of 12 inches if possible, to promote adequate root development.
Reduce weed competition for space, water and nutrition by covering the top of your raised bed with a second layer of landscape cloth (leave narrow open strips of soil for lettuce and other seeds, and cut holes in the cloth large enough to accommodate plants).
Respect the space requirements of your plants. While it is tempting to plant more closely than in a conventional garden bed, remember that your raised bed functions rather like a very large container, limiting the soil area into which plant roots can spread.
Remember that a raised bed needs regular watering and fertilizing, for the same reasons. While you may have created new garden space, roots cannot reach beyond the raised bed walls for moisture and nutrients.
Enhance your raised bed space by thinking vertically. While raised beds may not welcome vining crops like sweet peas, morning glories, pole beans, squash or cucumbers, training them up a bamboo pole/netting trellis will increase the variety of plants in your raised bed.