How to Build a Raised Garden Bed with Trex Decking (1’ Deep)


One of the top questions we hear from contractors, homeowners, and DIY-ers is, "What can I do with my scrap decking boards?" Nearly every building project will result in some excess material due to cutting materials to size, a desire to have a few spares on hand in case of mistakes, and a host of other factors. Our favorite way to turn these scrap deck boards into something functional is to create a raised garden bed. 

The best part? You don't need to build a deck first. You can always stop by your local lumber yard or retailer to pick up a couple of Trex deck boards to get started! Read on to learn how you can build an eco-friendly garden bed. 

2 1/2 Hours with a Team of One
Timing is estimated with two workers with intermediate carpentry skills.
*Times may vary
Step-by-Step Instructions
Chapter 01: How to Build a Raised Garden Bed with Trex Decking
Print Instructions

Step 1: Cut Side Pieces of the Garden Box

 Cut four (4) Trex boards at a 45-degree angle to be 5' long from tip to tip. These will create the two long sides of the garden box.

Next, cut four (4) Trex boards at a 45-degree angle to be 3' long from tip to tip. These will create the two short sides of the garden box. The 45-degree angle will allow you to hide the exposed ends of the boards.

Pro Tip

If cutting boards at a 45-degree angle is beyond your comfort level, cut the longer pieces to 5' and the shorter pieces to 2'10" using a straight angle. Note: with this method, the longer pieces will overhang the shorter pieces, and the cut end of the longer pieces will be visible.

Step 2: Cut Deck Boards for the Interior of the Garden Box

First, cut 12 short pieces of the decking to 11" long. These pieces will be mounted inside the garden box, and the side pieces cut in Step 1  will attach to them. 

Step 3: Build the Corners 

Attach two of the 11" pieces together to form a corner with the 2" composite deck screws that are color matched to your decking. Repeat this process to form 4 corners.

Pro Tip

Predrill with an 1/8" drill bit before creating the corner to avoid any splitting caused by drilling this close to the edge of the board.

Step 4: Attach the Long Side Boards

Stand the corner pieces on a flat surface. Place the first long 5' piece against the corner piece with the short point of the 45-degree angle at the edge of the corner piece where the two 11" pieces meet together. Fasten the 5' piece to the corner piece with two 2" color-matched composite deck screws. Repeat this process on the other end of the 5' piece.

Place the second 5' piece on top of the sides you attached in Step 4 and fasten to the corner pieces with two 2" color-matched screws. Repeat this process on the other side to create two 5' long sides.

Step 5: Attach the Short Side Boards

Place the first 3' piece against the corner pieces attached to the longer pieces. Fasten two 2" color-matched fasteners through the 3' piece and into the corner piece. Repeat this process on both ends and for the top 3' long piece. Repeat this process on the other end.

Step 6: Add Supports

Place two 11" pieces equal distance apart and fasten them to the 5' long pieces with two fasteners per 5' board. Repeat this process on both sides. These supports will brace the long pieces so they don't push out.

Step 7: Create Top Surface

Pro Tip

If you are purchasing materials for to create your raised garden beds as opposed to using scraps from a previous project, opt for Trex Transcend® Lineage™ deck boards for the top surface of your garden bed to create a cooler surface when gardening these beds.*

Cut your top pieces to the desired length for the overhang you would like.

Pro Tip

We recommend installing the top pieces centered on top of the two upright pieces for a clean look. 

Cut the two longer sides to 5'3 ½" to the long point of a 45-degree angle.  

Cut the two shorter pieces to 3'3 ½" to the long point of a 45-degree angle.

Fasten these pieces through the top into the side of the upright boards. Fasten every 16" with the 2" color-matched composite deck screws.

Pro Tip

Pre-drill the holes to avoid splitting the board while fastening into the side of the upright board.

Step 8: Add the Final Touches

Place the raised garden bed where you intend to keep it. Then, line the box with a weed mat material on the bottom and the interior sides of the garden bed. Fill the Trex garden bed with soil and let the gardening begin!


Circular Saw


Drill Bits


Speed Square

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2” Composite Color Matched Deck Screws

Weed Mat

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*Although Trex Transcend Lineage is designed to be cooler than most other composite decking products of a similar color, on a hot sunny day, it will get hot. On hot days, care should be taken to avoid extended contact between exposed skin and the deck surface, especially with young children and those with special needs.

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