How to Build a Wooden Planter Box (Simple Straight-Cut Build)

The material list is short. You need six 8-foot deck boards, two 8-foot pressure-treated 2x4s for the legs and braces, and a handful of 2-inch exterior screws. That's the whole shopping list.

Pedro used pressure-treated lumber because this box holds flowers. If you plan to grow food in yours, switch to cedar or line the inside with plastic so nothing leaches into the soil. Either way, use exterior screws so the joints hold up outdoors.

Every cut here is straight, so a miter saw or a circular saw both work. Cut eight 2x4 legs at 16 inches. Cut four deck boards at 16 inches for the sides. Cut four more deck boards at 48 inches for the front and back.

Mark each piece with a pencil and a speed square before you cut so your ends stay square. Keeping the legs identical is what makes the box sit flat later, so measure twice on those.

Stand two legs up and lay a 48-inch deck board across them. Screw through the board into the legs, driving the screws from the inside out so the heads never show on the finished face. Put about three screws into each leg.

Keep the board flush with the top and bottom of the legs before you drive anything. Pedro stacked a second board underneath the first and staggered the screws slightly, which gives the joint a little more strength.

Attach the second leg piece to the end of your front-and-back assembly, flush with the top of the first leg. Drive about three screws through it into the leg behind it.

Set these screws about three-quarters of an inch up from the bottom edge so they land in the middle of the inch-and-a-half-thick 2x4. These heads will show on the outside, but the side boards go on next and hide most of the joint.

The 16-inch side boards close up the box. Working solo, Pedro clamped each side board to the frame at the top so it stayed put while he worked. Make sure the board is flush at the top and pressed tight against the leg so the legs don't spread apart.

Screw from the inside into the leg. Get a couple of screws in, pop the clamps off, then add one more screw at the very top for good measure. Repeat on the other side.

Cut three 16-inch braces from the leftover 2x4. Drop one at each end and one in the middle of the box, flush with the bottom of the front and back boards. A tight fit is a good sign here.

Screw through the front deck board into each brace, then through the back. Don't try to screw down through the top of the brace, your screws won't reach it. On the end braces, add a screw or two through the side boards too.

Measure the inside length of the box. Pedro's came out to 46 inches, so he cut three deck boards at 46 inches. Drop them in across the braces and they should sit snug.

The last board almost never fits full width, so rip it narrower to fill the gap. Pedro ripped his to about four and a half inches and left a small space on purpose. That gap gives extra water somewhere to drain.

A planter needs drainage or the roots sit in water and rot. Drill several holes through the bottom boards. Pedro used a half-inch Forstner bit, which cuts a clean flat-bottomed hole.

Scatter the holes around and steer clear of the center brace so your bit doesn't hit it. Half an inch is a good size. Go bigger and soil washes out, go smaller and it clogs. If you're worried about soil loss, lay landscape fabric over the bottom before you fill it.

That's the whole build. Simple design, nice and sturdy, and every cut was straight. Give the outside a quick pass with an orbital sander to knock down any rough edges and splinters.

Pressure-treated wood can go outside as is, but a coat of exterior stain or sealer deepens the color and buys you years of extra life. Then line it with landscape fabric, fill it with potting mix, and plant your flowers.