Composite lumber makes them rotproof

Thanks to a recently developed building material–composite lumber, designed for decking–you can build rotproof raised beds. The triangular bed shown here is made with Trex, a composite of recycled plastic bags and wood fibers (Trex; 800/289-8739 or Trex comes in 52-inch 4-by-4s for posts (available soon) and 2-by-6s for sides and tops. If you need rectangular planters, you can modify this design.

Composite-lumber advice

It’s heavy, so build the planter in sections that can be screwed together on-site.

If the planter is no more than three boards high (about 16 inches tall) and the site is flat, the posts can just rest on the ground (as shown here). You’ll need longer posts for in-ground installations.

Assemble with screws. If you are using standard deck screws, drill the holes first, since composite lumber is dense and hard. A self-drilling deck screw, designed for working with products such as Trex, is available; it’s called Fastap Poly² (800/847-4714 or Use 3-inch-long screws. 

TIME: One day

COST: About $160


• Three 52-inch Trex 4-by-4s
• Three 10-foot-long Trex 2-by-6s
• One 14-foot-long Trex 2-by-6
• 100 3-inch deck screws (Fastap Poly²)
• One 9-inch-long step bracket
• 12 11/4-inch machine screws

TOOLS: Tape measure, pencil, circular saw, combination square, framing square, electric drill


1. From the 4-by-4s, cut seven 161/2-inch lengths (which should be equal to the width of three 2-by-6s).

2. The sides of the planters are made of three 2-by-6 boards with mitered ends. From each 10-foot 2-by-6, cut one 481/2-inch length (A) and two 321/2-inch lengths (B). Cut 45º miters on ends of all boards.

3. From the 14-foot piece, cut one top piece at 671/2 inches (C) and two at 393/4 inches (D). Miter the boards at 45º across their width.

4. Using the combination square, measure and mark lines 3 inches in from both ends of the longest sides of boards A and B, extending the lines over edges of boards; these will help you align the posts.

5. Place two posts on a flat work surface. Place three side boards on top of them, aligning the outer edges of the posts with the lines drawn in step 4. Check alignment with a framing square, then drive two screws through each side piece into each post. Repeat for other two sides, centering third post on the As.

6. Stand short (B) sides upright so mitered edges of one end meet in a right angle. Using 11/4-inch screws, join them with the step bracket on the inside face.

7. Butt the long (A) side against the ends of the short sides. Join with screws through As and into the ends of the Bs.

8. Place top boards flat, covering the tops of all posts and sides; secure with screws.

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