How to Build a Planter Box (Beginner Guide)

Build a simple slatted planter box from 1x6 boards. Learn repeat cuts with a stop block, pilot holes, real drainage, and how to choose outdoor timber.

What you're making

A four-sided box for herbs, salad leaves or flowers, made from straight boards screwed to four corner posts. It is the fourth build in the beginner project progression on the projects hub, and the first one where the same cut has to come out right eight times in a row.

There is no clever joint here. If your pieces match and your screws sit in pilot holes, the box will look square and stay square. If they do not match, every mismatch lands at a corner where you can see it, which is exactly why this is a good build to learn on.

What it costs and how long

An afternoon for cutting and assembly, plus drying time if you finish it. A first attempt runs longer than you expect, and the extra time goes into marking, not sawing.

Cost depends on the species you pick and what timber costs where you live. Construction-grade pine is usually the cheapest and easiest to cut; cedar and redwood cost more and resist rot better. How the common beginner timbers differ is set out in choosing wood as a beginner. Buy boards for one box only until you have built one, because you will change the dimensions the second time.

Cut list

Nominal lumber names are not actual sizes. A "1x6" is about 19 x 140 mm once dried and planed, and a "2x2" is closer to 38 x 38 mm. Names and stock sizes differ by country, so measure the board in your hand before you commit to a cut.

Cut the sides and posts first, assemble the box, then measure the real inside dimensions and cut the bottom parts to fit. That order removes the arithmetic that trips most people up.

Before you start

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Work on a bench, a workmate or a solid table with room on one side. Clamp every board before you cut it; never hold a board with one hand and saw with the other. Wear eye protection any time you cut, drill, drive or sand, hearing protection for any power tool, and a fine-particle dust mask before sanding. Guards stay on, never defeat a safety switch, and take the battery out before changing a bit or clearing a jam. Keep gloves and loose sleeves away from a spinning bit. All of this supplements your own tool's manual, and that manual wins. The fuller checklist is on woodworking safety for beginners, and safety glasses, ear defenders and a dust mask is the cheapest part of the build.

Stop and ask for help if you are holding a board and cannot tell what it is. Reclaimed timber may be pressure-treated, coated with something old, or full of hidden fasteners, and pressure-treated timber has to be handled the way its own instructions say. Do not cut, sand or burn a board of unknown origin to find out what it is - buy a new one, since at this size the difference is a few dollars. The same applies to a planter destined for a balcony rail or anywhere it could fall onto someone below: that is a fixing question, not a woodworking one, and worth asking someone qualified about first.

A drill/driver does the whole assembly here, so if you are buying one tool for this project, make it that one. A cordless drill/driver kit with a second battery will outlast every project on this site, and the beginner power tool path explains what it actually needs to do before you spend more.

Step 1: Make one piece the master

Measure and cut a single long side. Check the cut with a square, and check that the piece is actually the length you wanted. That one board is now your pattern, and the tape measure goes back in the drawer.

Step 2: Set up a stop block or a story stick

This is the skill the project exists to teach. Clamp a scrap block to your mitre box or saw guide so the board can only slide in that far; every cut then lands in the same place without you reading a number again. With no jig, lay the master piece on the next board, mark against its end with a knife or sharp pencil, and cut to that mark. The habits behind it are in measuring and marking for beginners, and a combination square and tape measure is the pair worth owning first.

What "right" looks like: stack the four long slats face to face and stand them on end. The tops should form one flat surface with no step you can feel with a fingernail.

Step 3: Cut the rest

Cut all four long slats, all four short slats and the four posts against the same stop. Keep the offcuts - they are useful for test screws now, and for the small builds that use up offcuts later.

Step 4: Drill pilot holes

Every screw going near the end of a board needs a pilot hole, and one going into end grain needs it badly. A pilot hole roughly matches the screw's inner shank, not its threads. Test on an offcut of the same board first: the screw should pull the two pieces together and stop, with no crack running along the grain. Countersink so the head finishes flush. Bit sizing is covered in drilling and driving.

Step 5: Build two sides, then join them

Lay two long slats against two posts, edges aligned, with the slats overhanging each post equally. Clamp, then drive two screws through each slat into each post. Repeat for the other long side, and you have two ladder-like panels.

Stand those panels up and screw the short slats across the ends into the same posts. Check for square by measuring corner to corner both ways. The two diagonals should match. Nudge the box until they do, then drive the last screws.

Step 6: Cleats, bottom and drainage

Screw the two cleats to the inside faces of the long sides, near the bottom and level with each other. Rest the bottom slats on them with roughly a finger-width gap between each one, then screw them down.

Drill drainage holes through each bottom slat as well, because gaps alone can clog with compacted soil and roots. A solid, sealed bottom is the fastest way to destroy a wooden planter: the timber stays saturated from both sides and rot starts where you cannot see it.

If you use a liner, use landscape fabric or a punctured plastic sheet, staple it around the inside, and cut a slit over every drainage hole. A liner keeps soil off the timber; it does not replace drainage, and a liner with no holes turns the box into a bucket.

Where beginners go wrong

• Measuring eight times instead of once. Eight measurements produce eight small errors, and every one shows at a corner. One master piece and a stop block produce one error at worst.
• Skipping pilot holes. A screw driven straight into the end of a dry pine board will split it, usually on the last quarter turn, usually on the piece you cut best.
• Indoor screws outdoors. Plain steel rusts and bleeds dark streaks down the wood once weather gets at it. Use screws sold for exterior or deck use.
• Standing the box flat on wet ground. Soil or a puddled patio wicks water straight into the end grain of the posts. Leave the posts long as feet, or stand the box on two strips of scrap.
• Sealing the inside to "protect" it. A film finish inside traps water against the wood. Leave it bare so it can dry between waterings.

Finishing it

Sand the outside faces and every edge you will handle. Start around 80 or 100 grit if the boards are rough, then 120, then 150, and take the sharp corners off with a few strokes. Eased edges hold a finish better and stop the box handing out splinters.

Three honest options: leave it bare and let it weather to grey, which is where most cedar planters end up anyway; use an exterior oil or stain, which has to be reapplied on a schedule set by your sun and rain rather than by any number anyone can quote you; or paint the outside only. Whatever you pick, read and follow the label on the can, including its storage and disposal instructions and its warning that rags soaked in an oil finish can self-heat. Spread those rags flat outdoors to dry, or dispose of them exactly as the maker states, and never leave them balled up in a bin. Do not finish the inside, and do not use an interior finish outdoors just because it is what you have.

The free First 5 Projects Roadmap lays out this build and the four around it in order, with the tool list for each, if you would rather work a progression than pick projects at random.

Make it yours

• Go deeper for root vegetables with a third row of slats and longer posts. Soil depth matters more than footprint for most edibles.
• Make it a trough - long and shallow - for a windowsill or a step, somewhere it cannot fall rather than on a rail.
• Leave gaps between the side slats for a lighter look. Less timber, faster drying, less soil held.

What to build next

Once repeat cuts and pilot holes feel routine, the next skill is drilling accurately into something you cannot take back to the bench. Move on to making a floating shelf, where the wall is part of the project.