Permanent Raised Bed Gardening: Bed Layout

Showing why 6-foot beds are too wide for most people.

At the Noble Foundation, our bed width of choice is 40 inches. This width combines the attributes of both narrow and wide beds.

Theoretically, beds can be constructed to any length. At the Foundation, most beds are 30 feet in length. A bed 40 inches wide and 30 feet long provides approximately 100 square feet of usable space. Most consumer fertilizer and pesticide products give rates of application on a 1,000 square feet basis. Moving the decimal one place to the left gives a rate for a 100-square-foot bed. This is the beauty of growing in this size of a raised garden – it makes computations easy! For example, 10 pounds of 13-13-13 fertilizer per 1,000-square-feet, a common rate for most garden soils, translates to one pound for the 100-square-foot garden.

Bed height is determined by the gardener's personal needs, budget and the nature of the materials with which the beds will be constructed. Most vegetable crops extract the vast majority of water and nutrients from the top 12 inches of soil. Any raised bed constructed on asphalt, concrete or other surface denying root penetration should be constructed to a height of 12 inches.

Good results have been obtained at the Noble Foundation in 6-inch high beds constructed over poor soil. A 6-inch-increase in soil depth above the existing grade will greatly enhance drainage.

Six-foot plastic mulch fits 40-inch-wide beds like a glove.

It appears that beds constructed 18 inches and above in height require extra fortification, often involving the need for anchored support columns or posts. High beds constructed of such materials as corrugated sheet metal require support posts because they lack rigidity.

By contrast, railroad ties can be stacked several high without the need for support. Small box-type beds are able to stand alone without additional support. The 4-foot by 8-foot box bed made of interlocking landscape timbers is an example of a stand-alone bed. Plan on "beefing up" any raised bed that will double for a bench.