How to Build Raised Beds
Raised beds are a good way to grow healthy plants in areas that are poorly drained or extremely rocky. Raised bed kits are sold commercially, but more economical raised beds can be built using construction materials.
Pressure-treated micronized-copper-treated two-by-six, two-by-eight, two-by-10 and two-by-12 lumber can safely be used. The micronized copper helps prevent the wood from rotting, and the copper in the wood is an essential element. Never use CCA-pressure-treated wood because it contains arsenic that can be absorbed by the roots of plants.
Pressure-treated two-by-six and two-by-eight lumber should only be used when the soil beneath the bed is well drained. In areas where the soil is poorly drained, two-by-10 and two-by-12 provide adequate drainage and sufficient depth for good root growth.
Other materials that can be used include cement blocks and cement boards. If you live near a factory that makes cement blocks, you can purchase second-grade or damaged blocks at a much lower price than construction-grade blocks. When using cement blocks, beds should be no less than two blocks high. The blocks are laid with the holes facing up. Filling the holes with crushed stone or coarse gravel helps keep them in place. Cement board is generally available in four-by-six-foot sheets and is easily cut with a masonry blade on a skill saw.
Sides made of lumber and cement board must be supported using two-foot-long one-half- or three-quarter-inch pipe or concrete reinforcing rebar. Both pipe and rebar should be pounded into the ground sufficiently deep that the tops are at least one inch below the top of the sides.
Before installing the sides of the raised beds, eradicate perennial weeds. Skim off the first one to two inches of topsoil as it contains millions of weed seeds. If the soil is well drained and the sides are only six to eight inches high, rototill the existing soil before installing the sides. Rototilling first helps prevent an interface between the existing soil and the imported soil.
The soil used for filling the beds can either be an imported or manufactured topsoil. If you are going to purchase imported topsoil, specify that it be a sandy loam soil containing a minimum of 60 percent sand and 10 percent clay with at least 3 percent organic matter. You should also specify that it be free of stones, roots, fabricated innerts (glass, plastics and metal) and pesticides. A manufactured topsoil such as equal parts by volume of sandy loam topsoil, compost and pine vines or loam, compost and builders sand can be easily blended.
With manufactured topsoil, fill the beds to the top edge of the side-boards to allow for settling. For imported top oil, fill the beds to within one inch of the top edge of the sideboards. Place an inch of compost over the imported topsoil and rototill. After the soil is in place, take at least five samples from different parts of the raised beds and submit one composite sample for testing of all elements required for plant growth.
Follow the recommendations of the soil test results and incorporate recommended nutrients thoroughly before doing any planting.
Send soil samples for testing to Waypoint Analytical in Richmond. Full instructions for testing are online: www.soilandplantlaboratory.com/
services/soilsampling.aspx.