Overview

raised planting bed diagram
Illustration: Gregory Nemec
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A raised bed is nothing more than a giant planter, a box of topsoil with timbers for sides. You can build it in any sunny, level spot, or you can excavate a slightly sloping location to create a level surface (though this adds to the digging). The box itself can be made from any size lumber—the larger the pieces, the fewer you'll need. Cedar or redwood timbers look nice and are naturally weather-resistant. Pressure-treated wood is a less expensive, albeit less polished, alternative, and preliminary EPA tests have shown today's treated lumber to be a safe material for use in vegetable and herb beds.

Before you build your bed, you'll need to figure out how big you want it to be. "The beauty of a raised bed is its accessibility," says This Old House landscape contractor Roger Cook. "It should rise at least a foot off the ground—this gives the plant roots room to grow and gives the gardener's back a break." Stick with 4 feet or less for the width, says Roger, so you can reach the middle of the plantings from either side; when it comes to length, the limit depends on the size of your lumber. If you use the same beefy 6x6 timbers shown here, you shouldn't go beyond 10 feet because the timbers will get too heavy. To cover a larger area, build side-by-side beds with room to walk between them. Because the bed's first timbers are partially buried, you'll need to guard against rot by laying 2 inches of gravel beneath them. This promotes drainage and also provides a solid footing. For the bed itself, line the bottom with more gravel and drill weep holes through the timbers' sides.

Most of the precision and muscle work in building the bed comes in digging the trenches and leveling and squaring up the first course of timbers. Once the first course is laid properly and spiked to the earth with rebar, assembling the rest of the bed is a matter of piecing the sides together like building blocks. The whole thing fastens together with timber screws. Then you simply add a railing, shovel in the topsoil, and plant your new garden.
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    Tools List

    • circular saw
      Circular saw
    • hand saw
      Handsaw
    • trenching spade
      Spade
    • trenching shovel
      Trenching shovel
    • hand hoe
      Hoe
    • framing square
      Framing square
    • four-foot level
      4-foot level
    • drill
      Drill/driver with an extended 1/2-inch spade bit
    • sledge hammer
      Sledgehammer,
      to drive rebar
    • speed square
      Speed square
    • caulk gun
      Caulking gun
    • hack saw
      Hacksaw,
      to cut rebar, optional

    Shopping List

    1. 6X6 TIMBERS

    The bed’s 4 sides each need 3 courses of timbers to rise more than a foot above ground, for a total of 12 timbers. Because it’s best to have full pieces on each side, buy stock lengths at least as long as the dimensions of your bed. Make sure each timber is straight and clear of knots on at least one side.



    2. 2X8 LUMBER

    to make a railing to cap the bed’s walls



    3. 1/2-INCH REBAR

    to secure the first course of timbers to the ground. These are usually sold in 18- to 24-inch lengths. Both are long enough to secure 6x6 timbers at least a foot into the ground.



    4. 10-INCH SELF-TAPPING TIMBER SCREWS

    such as Timberlok and Timbrex brands, to fasten the sides together.



    5. CONSTRUCTION ADHESIVE

    to fasten the railing to the timbers



    6. PEA GRAVEL

    for drainage under the walls and at the base of the bed. Most home centers carry either 1/2- or 1-cubic-foot bags. To determine the cubic footage you’ll need for 3 inches of fill at the base, divide the square footage of your bed by 4. To figure out how much you’ll need for 2 inches of fill under the timbers, add the length and width of the bed (in feet) and divide that number by 6.



    7. TOPSOIL/COMPOST MIX

    Most home centers carry 2- or 3-cubic-foot bags of properly amended soil. Because the bed is just about 1 foot deep (with the gravel layer at the bottom), the square footage of the bed roughly equals the cubic footage of soil you’ll need to fill it. Throw in an extra bag to account for settling.



    8. 3-INCH DECK SCREWS

    For fastening 2x8 cap rails.