So last summer’s homegrown tomato crop was more of a bummer than a bumper, and after a few exploratory backyard digs it seems less likely that you’re going to hit pay dirt. But that doesn’t mean going hungry. By building a raised planting bed, you can set up your seedlings with a loamy home as fecund as the Fertile Crescent.
Surrounded by timbers and filled with rich soil, the raised bed lets you customize your plants’ nutrients and moisture. It also brings the garden to the gardener, allowing you to easily maintain your plants without stooping.
And if you build it early you can get a head start on the planting season because the elevated soil heats up sooner than the ground. Then not only will the handsome structure help define your garden but never again will bad dirt stand between you and a good BLT. Learn how to build a raised flower bed in the steps below.
Raised Planting Bed Overview
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 6×6 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.
Mark the bed’s outline
The timbers that make up the walls of the bed will butt against one another end-to-side at the corners. So to determine how long to make the timbers, subtract 5 ½ inches (the true width of a 6×6) from the length of each side. Using a circular saw and handsaw, cut 12 timbers to length.
Clear the site of obstructions and arrange 4 timbers in an outline of the planned bed, butting each timber’s end against the next timber’s side. Using a spade or square-edged shovel, mark the bed’s outline by cutting vertically through the turf both inside and outside the loose-laid timbers’ perimeter.
Dig trenches for the walls
Set aside the timbers. Using a spade, remove all the turf within the outer lines. Switch to a trenching shovel and dig a 6-inch-deep trench in the outline of the timbers.
Fill the trench with 2 inches of gravel. Use a hoe to spread the gravel level.
Tip: Roll up the turf you remove and reuse it to patch your lawn. Place the soil you dig out onto a tarp and use it inside the finished bed.
Set the first course of timbers
Using a drill/driver fitted with a ½-inch extended spade bit, drill holes through the four base timbers every 2 feet.
Lay the timbers in the trenches with all the pilot holes vertical. Arrange them so the butt end of one meets the side of the next in a clockwise fashion.
Using a 4-foot level and framing square, level and square the four timbers, adding or removing gravel as necessary.
Place the level atop a scrap of lumber laid diagonally across the timbers to check for level corner to corner.
Fasten the frame with rebar
Using a sledgehammer, drive a length of rebar through the pilot holes in the timbers and at least 1 foot into the ground. Check the frame for level and square as you proceed.
Hammer each rebar flush with the top surface of the four timbers, being careful not to hit the frame so hard that you knock it out of level.
Tip: To cut rebar to length, saw halfway through with a hacksaw, then bend to break.
Assemble the bed’s walls
Lay the next course of timbers on top of the base course, but arrange them counterclockwise so they overlap at the corners in the opposite direction from the first course. This will create a lapped pattern.
Using a drill/driver, drive timber screws down through the top course and into the timber beneath, two at each corner and one in the center of each side.
Drill weep holes
Using an extended ½-inch spade bit, drill weep holes for drainage through the second course every 4 feet. Drill from the outside in, to keep the holes looking neat, and angle the bit upward so water will flow out.
Lay the third course of timbers clockwise on top of the second, lapping the corners again. Fasten them to the second course with timber screws in the same manner.
Tip: Slip a short length of ⅜-inch copper pipe into the weep holes to protect the wood and make clearing clogs easier.
Install the cap railing
Lay a 2×8 board on top of one wall. Line it up flush with the inside edge. Mark the board where it meets the inner corners. Using a speed square, extend this mark at a 45-degree angle projecting outward.
Using a circular saw guided by the square, cut the ends at 45-degree miters. Repeat this process on the other three sides of the bed until you have a frame of 2x8s that sits flush with the inner edge of the bed and protrudes 2 inches over the outer edge.
Apply construction adhesive along the top of the timbers and on the board’s mitered edges. Lay the boards in place. Fasten them to the timbers with 3-inch decking screws every 12 to 16 inches. Drill a horizontal pilot hole through the rails edge and across the mitered corner. Drive a 3-inch screw into the joint to prevent it from opening.
Fill the bed
Shovel a 3-inch layer of gravel across the bottom of the bed and smooth it with the hoe.
Fill the bed with topsoil, tamping it lightly every 6 inches to reduce settling later.
Fill to within 2 to 3 inches of the top of the bed. Rake the soil smooth and plant. [external_footer]