How to Build a Modern Planter
Build it any size you like—in one afternoon.
A few hours
IntroductionA modern planter like this is super simple to build. And it’ll last a long, long time because there’s no soil-to-wood contact—and therefore no rot. Instead, the soil is contained in a plastic planter inside the wooden planter. The only part that touches the ground is never-rust aluminum. You’ll find everything you need for this project at a home center.
- Caulk gun
- Circular saw
- Miter saw
- 1 in. drywall screws
- 1 qt. of finish
- 1-1/16-in. aluminum angle
- 1-1/4" exterior wood screws
- 1-in. aluminum tubing
- 1x4 board
- 2-in. exterior screws
- 2x4 board
- 5/4x6 x 8-ft. deck boards
- Plastic planters
- Silicone caulk
Choose your plastic planters first
The plastic planters (called “liners” from here on) determine the shape and size of the planter boxes, so shop for those first. Choose ones with sturdy plastic lips that can support the weight of the plants and soil. Your planter shapes can range from square to long, narrow rectangles; it all depends on the liner sizes and how you decide to configure them. You can adjust the height of your planters simply by using more or fewer rings of decking boards (Photo 4). But if you make your planters shorter, be sure the liners will clear the ground when they’re in place.
Buying the materials
We built our planters from 5/4×6 cedar decking (1 in. thick and 5-1/2 in. wide), the standard dimensions for decking. If you plan to stain your planters, you can save 30 to 40 bucks by substituting treated decking boards. If your planters will rest on a composite deck, you may want to choose matching or contrasting composite decking. To help you determine the quantity and length of the boards you’ll need, do a bit of figuring with your liners upside down on the workbench (Photos 1 and 2). At the same time, figure out how many treated 1x4s to get for the inner structure (Figure A). You’ll need at least two 8-ft. lengths for the corners and more for the liner ledger boards (Photo 6). You’ll also need a short length of treated 2×4 for the diagonal bracing (Photo 8).
The corners are cloaked with 1-1/16-in. aluminum angle. Buy 3-ft. lengths if you’re building only one planter. If you want to build more, buy 4-ft. lengths and make the feet 2 in. high rather than 3 in. That way you can get feet for two planters from this rather expensive material. We used 3-in. lengths of aluminum square tubing to support the weight of the planter. But you’ll only use about a foot of a 3-ft. length ($10). If you want to save a few bucks, you can substitute 1×1 treated wood blocks that you cut yourself.
Modern Planter Project Plan – Figure A
Assembling the planters
Measure and cut the deck boards to length (Photos 1 and 2). It doesn’t matter which two sides you choose to overlap the ends. Apply a finish if you choose (see below) and assemble each ring with 2-in. exterior screws (Photo 3). After you build the first ring, test-fit the liner(s). It’s easy to confuse side and end boards, especially if the planters are nearly square. Then just follow the how-to photos to complete the planters.
We used PPG Timeless oil finish (Mahogany). Whatever finish you choose, apply it before assembling the rings. You’ll avoid slopping finish onto the aluminum corners, and if you’re using cedar, you’ll be able to seal the ends to prevent rot. We finished all four sides so we could choose the prettiest “show side” when we built the rings. Let the finish dry completely before gluing on the aluminum corners or they won’t stick. If you’re impatient, choose a water-based finish. If you go with oil-based, your three-hour project may become a three-day one.
Project step-by-step (10)
Figure out the length of your side boards
Lay out the liners, decking boards and a 1/4-in. shim to establish the length of the side boards.
Establish the length of the end boards
Measure a liner plus a 1/4-in. shim to determine the length of the end boards (Photo 3). Cut eight boards of each length and apply finish to all four sides and the ends.
Assemble the planter rings
Clamp and screw together each ring of deck boards with two 2-in. exterior screws. Choose the best-looking board sides to face outward.
Stack the rings
Clamp the rings together and tap the corners into alignment with a hammer.
Find the lip height
Measure the liner lip height and cut a gauge block to a width that size.
Install the liner ledger
Cut the ledger boards to fit. Then, using the gauge block to position them, screw them into place with 1-1/4-in. screws spaced every 6 in.
Tie the rings together
Cut and install 18-in. 1×4 corner blocks to the inside corners with 1-1/4-in. screws, two into each deck board.
Mark the diagonal brace
Rest the planter upside down. Center a 2×4 over opposite corners and scribe the angle cuts, then cut them with a circular saw.
Add the diagonal brace
Support the brace on 2×4 scraps while you toe-screw it to the inside corners with 2-in. screws.
Working with the aluminum parts
You can cut aluminum with a hacksaw, a jigsaw, or a miter saw fitted with a carbide blade. Wear eye and hearing protection. If you use a miter saw, cut slowly. The aluminum corner trim adds style and hides the end grain of the decking. It’s best to attach it with clear silicone caulk instead of construction adhesive. Either product will likely squeeze out a bit when you clamp on the corners (Photo 10), and it’s no fun cleaning up colored adhesive from all the joints. That said, keep the silicone bead about 1/2 in. away from the outside corners of the decking to minimize squeeze-out.
Cut the 1-in. tubing support blocks to span all the way from the base of the feet to the bottom of the planter (Photo 11). They support the entire weight of the planter and the soil-filled liners.
Glue on the corner trim legs
Cut four 25-in. aluminum angle corner trim pieces. Then apply a bead of silicone caulk to the corners and clamp each one into place.
Add the support blocks
Cut, glue and silicone the 1-in. square aluminum tubing support blocks to the inside of the aluminum angle corners.
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