Raised bed heights will vary depending on the site. For example, temporary raised beds created for one season of growing may be just 8 inches off the ground. A terraced bed built into a hillside may be 24 inches or taller. Beds planted in public areas or private gardens near concrete-paved walkways benefit from several feet of height to prevent plant heat stress.
Since most plants root are least 1 foot deep, University of Missouri Extension officials suggest that beds be 2 feet deep for most walled, raised beds. Although some plants will root deeper than 12 inches, the typical garden plant roots between 6 inches and 1 foot. By providing 2 feet, you allow the roots plenty of room to stretch out, as well as providing more soil to carry water and nutrients to plants as they grow.
A bed raised 27 to 33 inches provides a table height garden, easily accessible by people in wheelchairs or those with mobility challenges.These beds may be positioned on sturdy legs with a container on top for the plants, or built with walls from the ground up like a large box. The latter style of raised garden will require a large amount of bedding media, so calculate the square footage and volume before building.