How to Build a Raised Garden Bed with Steel and Redwood

Looking for a durable, affordable raised garden bed that will last for years? This DIY project combines galvanized steel and redwood for a sturdy, long-lasting planter that costs under $75 and takes just a couple of hours to build. Follow along to create your own 4x8 foot garden bed.

Materials:

• 1 piece of 4x4 x 8ft redwood (for corner supports)
• 3 pieces of 1x6 x 8ft redwood (for caps/trim)
• 1 sheet of 12ft x 26in galvanized steel roofing panel
• Metal roofing screws with washers (self-tapping)
• Wood screws

Tools:

• Angle grinder with metal cutoff wheel
• Circular saw (or miter saw with sliding capability)
• Speed square
• Screw gun with 1/4in hex bit
• Measuring tape
• Safety glasses and hearing protection

Step 1: Cut the 4x4 Posts

Cut your 4x4 redwood post into six 14-inch support pieces. These will serve as the corner and middle supports for the sheet metal sides.

Step 2: Cut the Sheet Metal

Lay your 12ft galvanized steel panel on top of scrap 4x4 pieces, leaving a gap in the middle for support. This prevents cutting directly on the ground.

Safety warning: Always wear eye protection and hearing protection when using an angle grinder—it throws sparks and is very loud.

First, cut the 26-1/8 inch wide panel in half lengthwise (cut at 13-1/8 inches). Then cut the following pieces:

• Long sides: Cut two pieces at 92 inches each
• Short sides: Cut two pieces at 44 inches each

Note: These dimensions are slightly less than 4ft x 8ft to account for the 1x6 caps, creating a better finished look.

Step 3: Assemble the Sides

For each long side piece, lay out three 4x4 posts—one in the middle and one on each end. Position the cut edge of the metal toward the bottom (this overhang will go into the ground for extra support).

Attach the sheet metal to the posts using roofing screws:

• Place two screws per post (one at top, one at bottom)
• Leave about 1/8 inch gap between the metal and the post edge
• The self-tapping screws won't require pre-drilling
• When you drive the screw in, it will pull the metal flush with the post

Repeat this process for all four sides.

Step 4: Assemble the Box

Connect the four sides together to form your rectangular box. Make sure everything is square before moving to the next step.

Step 5: Cut and Install the 1x6 Caps

Cut your 1x6 redwood boards at 45-degree angles for mitered corners:

1. Cut the long side caps first and install them
2. Then measure and cut the short side caps to fit (this ensures tight seams)

Use a circular saw with a speed square, or a miter saw if available. Secure the caps with wood screws, making sure the corner of each cap matches up with the inner corner of the 4x4 post.

Step 6: Final Adjustments

If your mitered corners aren't fitting flush, you may need to adjust the box slightly. Simply remove the screws on the loose side and reposition the metal until the seams line up properly.

1. Cut over supports, not the ground – When cutting sheet metal with an angle grinder, always lay it over scrap wood to prevent sparks from damaging your work surface.

1. Account for cap width – Shorten your sides slightly (as shown in this guide) so the 1x6 caps sit centered on the 4x4 posts rather than extending into the growing area. This saves soil and creates a sturdier edge to lean on.

1. Cut long caps first – Install the long side caps before cutting the short side pieces. This allows you to measure the exact gap for a perfect fit.

1. Check your square – If mitered corners don't line up, your box might not be square. Adjust the sheet metal position before finalizing screws.

1. Leave the rough edge down – Position the cut edge of the sheet metal at the bottom where it will be buried in the ground for a cleaner finished look.