How to Build a Simple Cedar Planter Box — A Beginner's Guide

A planter box is about the best first woodworking project there is. Cheap materials, forgiving joints, and something useful at the end of it. Here's how I'd build one.

I build doors for a living, but everybody starts somewhere, and a planter box is where I'd send a beginner every time. You don't need a shop full of tools or years of practice. You need straight cuts, a handful of screws, and about an afternoon. Get this one under your belt and you'll have the confidence to build the next thing. Let me walk you through it the way I'd explain it to somebody standing in the shop.

Why cedar

Cedar earns its keep outdoors. It's naturally rot- and bug-resistant, so it stands up to weather and wet soil without being treated. It's light, it cuts and screws easily, and it smells good while you work it. That combination is exactly what you want sitting out in the yard holding damp dirt all summer.

• Cedar — the easy pick: rot-resistant, forgiving, widely sold as fence pickets and 1x boards
• Redwood or cypress — also excellent if you can get them locally
• Skip pressure-treated lumber for anything growing food; the chemicals aren't worth it for a planter
• Pine works only if you seal it well, and it still won't last like cedar

What you'll need

Nothing exotic. If you've got a saw and a drill, you're in business.

• Cedar 1x6 boards (actual size about ¾" x 5½") for the four sides and the bottom slats
• A short length of cedar 2x2 for the four corner posts
• A couple of 1x2 cedar strips for the bottom cleats
• 1⅝" exterior or deck screws — coated or stainless so they don't rust and streak
• A saw (a circular saw, miter saw, or even a handsaw), a drill/driver, a tape measure, and a pencil
• A scrap of landscape fabric and a bit of sandpaper

A simple cut list

This builds a box roughly 18" long, 9" wide, and about 11" tall — a good size for herbs or flowers on a porch. Change the numbers to fit your spot; the method stays the same. Cut your long sides first, then measure your actual boards before cutting the ends, because real lumber is never exactly the size on the label.

• Long sides: 4 pieces of 1x6 @ 18" (two boards stacked per side)
• End pieces: 4 pieces of 1x6 @ 7½" (two per end — this length lets the ends tuck between the long sides)
• Corner posts: 4 pieces of 2x2 @ 11"
• Bottom cleats: 2 pieces of 1x2 @ about 15"
• Bottom slats: 3 or 4 pieces of 1x6 cut to drop inside, spaced with gaps

Putting it together

The whole trick is the corner posts. Instead of trying to screw the thin board edges to each other, you screw every board into a solid 2x2 post at the corner. It's strong, it's square, and it's dead simple.

• Build the two long sides first. Stand two 18" boards together and screw each one into a corner post at both ends. The post sits flush with the top and hangs down a hair at the bottom — you'll trim or hide that later. Now you've got two "walls," each with a post at both ends.
• Connect them with the ends. Stand the two long sides up and screw the 7½" end boards into the exposed faces of those same corner posts. When all four sides are on, you've got a box. Predrill near the ends of the boards so the cedar doesn't split.
• Add the bottom cleats. Screw a 1x2 strip along the inside bottom of each long side. These are the ledge your bottom slats will rest on.
• Drop in the bottom slats. Lay the slats across the cleats and leave a ¼" gap between each one. Those gaps are your drainage — don't close them up.
• Ease the edges. A quick pass with sandpaper knocks off the sharp corners and any splinters. You're done building.

Drainage — the part folks get wrong

If I could stand over your shoulder for one minute, it'd be for this. A planter with no way to shed water is a bucket, and a bucket rots the wood and drowns the roots. Water has to leave.

• Keep those ¼" gaps between the bottom slats, or if you used a solid bottom, drill five to seven ½" holes across it
• Lay a piece of landscape fabric over the bottom before you add soil — it keeps the dirt in while letting water run out
• Set the finished box up on a couple of small feet or scrap blocks so the bottom isn't sitting flat in a puddle

Do that and your box breathes. Skip it and no wood on earth will last.

Finishing it (or not)

Here's where I'll be honest with you: cedar doesn't need a finish. Left bare, it weathers to a soft silver-gray and lasts for years. That's a perfectly good choice and it's zero maintenance.

If you'd rather keep that warm cedar color, coat the outside only with a clear exterior wood oil and give it a fresh coat once a year. Leave the inside raw, or line it with plastic that has drainage holes punched through it. One rule: never seal the soil side with an interior varnish or paint — it traps moisture against the wood, which is the opposite of what you want. Cedar's whole advantage is that it can dry out.

Make it last

A few small habits stretch a planter box from a couple of seasons into many years:

• Use coated or stainless screws so you never get rust streaks bleeding down the sides
• Keep it up off wet ground and out of standing water
• Empty and dry it over winter if you can, or at least clear the drainage so it doesn't ice up full of soggy dirt
• A yearly coat of oil, if you're finishing it, keeps the color and slows the checking

That's the whole build. It's a good weekend project, and once you've made one you'll want to make three. And if you catch the bug and start dreaming about something bigger — a bench, a farm table, a real front door built to outlast the house — that's exactly the kind of work we do.