How to build a DIY planter box

Sometimes the planters at your local hardware store just aren’t enough. You’re missing… something. gravity Prestigious. Perhaps the satisfying scent of cedar. Fear not – building your own planter box out of cedar fence posts is a no-fuss afternoon project and can bring a new sense of style to your landscape decor.

While you can build a planter box out of pretty much any wood (pine is popular because it’s affordable), cedar is great for a number of reasons. First and foremost, it is rot-resistant, so that it can withstand years of weather, dirt and vermin, even if left untreated. Second, cedar pickets in particular are relatively inexpensive and easy to work with. Finally, cedar actively repels many types of insects, which is why this wood is so often used in cabinets. While scent doesn’t keep all garden pests at bay, it can deter some, including houseflies, ticks, mosquitoes, termites, and certain types of ants, according to the U.S. Department of Agriculture’s Agricultural Research Service.

This particular DIY planter box is a no-fuss and flexible project. The box I made is 12 inches square and 16 inches high, but you can easily make one with a 16 x 16 inch or 24 x 24 inch base by changing the dimensions below. Bigger than that and you’ll probably have to switch to a long planter box design.


  • Time: 2 to 3 hours
  • Material costs: $30 to $50
  • Difficulty: moderate


How to build a cedar planter box

1. Cut the fence pickets to rough length. Before bending the wood properly, always cut it to rough length first. You can use a miter saw to cut the fence posts into sections, but I did it on my table saw with a cross-cut slide instead because I had them set up already. Cutting the wood into shorter lengths before routing reduces the amount of material you need to remove to create flat surfaces.

2. Join edges and cut slats to final length. For this project I chose not to flatten the faces of the fence posts. They were pretty flat to begin with, and I didn’t want to lose the rough, rustic look of the boards to the planer. I joined the edges with a plane on my table saw and then trimmed the boards to final length with my cross-section sled.

The final cut list for this project is:

  • 4 wide sidewall legs (2.5 x 16 inches)
  • 4 narrow sidewall legs (2 x 16 inches)
  • 8 wide sidewall boards (3 x 11 inches)
  • 8 narrow sidewall boards (3 x 10 inches)
  • 4 top miter frames (1.5″ x 15″)
  • 3 base boards (3.5 x 11 inches) (you will trim these to fit exactly once you have the box assembled)

3. Roughly sand all boards. As mentioned, I didn’t want to lose the rustic look of the fence posts. However, they were still quite rough and I was afraid that if I left them untouched, people would get splinters while planting. So I spent some time with my random orbit sander and 120 grit sandpaper to smooth both sides of all the boards. How long you sand is entirely up to your aesthetic preferences, but it only took me about a minute per side to remove any loose or jagged material. I smoothed out the top miter boards and the legs a little more than the other boards – they’ll be the ones people touch the most.

4. Separate the boards for the four side panels. The 11″ plates fit the 2.5″ wide legs and the 10″ plates fit the 2″ legs. Don’t forget this, or you’ll end up with a rectangular box instead of a square.

[Related: Benefit your neighborhood bats with this DIY bat box]

5. Build the side panels. With a piece of ½ inch plywood and a speed square you can make a simple jig for aligning the boards. First, lay one leg on your assembly table, with the long edge flush against the flat edge of the plywood. Line up the speed square along the same plywood edge, touching the top of the leg and protruding into the plywood. Then smear wood glue on the leg, leaving about ¾ inch on the edge farthest from the plywood.

The large sheet of plywood on the left acts as an alignment jig, helping you ensure the sidewall leg (right) lines up with the top panel of the panel (top). The upright piece here is the spacer for the hinge where the other side panel connects to this one. Jean Levasseur

Lay the top panel on the plywood and extend it onto the glued section of the leg. You must leave enough room for the other panel’s leg as the panel legs will snap together during assembly. So use one of the extra boards as a spacer – lay it, tip on it’s side, along the outside edge of the leg board inside the area you left clean. Align a dash panel with the speed square, flush with the top of the leg, and slide it over it so it just touches the spacer plate. Once positioned and square, nail to hold alignment. Then add the bottom three boards using the top panel board and spacer for alignment and nail these in place. Finally, turn the nearly completed side panel over and glue and nail the second leg to the other end of the panel boards using the speed angle and spacer to align.

Repeat this step for the three remaining panels.

6. Add moldings to the inside of two side panels. Before assembling the planter box, add small strips to either both wide panels or both narrow panels. It doesn’t matter which panels get those ledges as long as they’re the same size. The ledges hold the boards for the bottom of the box, so they need to face each other. It’s much easier to do this before assembly, so don’t skip this step.

I used the scraps I cut off when I cut the legs to width. To attach, I cut the scraps to 9 ½ inch lengths, then glued and Brad nailed them in place.

  • Note: I added two rows of ledges so I can adjust the depth of my planter if needed. The first is 6 inches below the top of the panel and the second is 9 inches below.

7. Assemble the box. This is an easy assembly, but be careful. The most important thing to remember is that the narrow panels sit inside the wide panels. This turns the planter into a square – if the wide panels sit in the narrow ones, you get a rectangle.

To assemble, spread glue on the inside edge of the legs where you placed the spacer plate in step 5. Then lock all the boards together and set them on a flat surface like your assembly table or table saw. This will keep the bottoms of the legs flush with each other to keep the planter from wobbling.

Once the boards are interlocked, add corner clamps to the top to keep everything square and in place. Then wrap the strap clips around the outside of the box and tighten. I used two straps, one about an inch from the top and the other about an inch from the bottom of the panels.

Make sure all corners of your planter box are square. Measure from one corner to the opposite and then between the other two – both diagonals should be the same length.

  • Note: If you don’t have belt clamps and/or corner clamps, use regular clamps.
A DIY cedar planter box assembled, glued, clamped and placed on a table in the middle of a wood workshop.
The fully bonded and clamped assembly. Jean Levasseur

8. Cut the boards for the base. Exact measurements will vary somewhat depending on how thick the boards were to start with and how much material you sanded away. My boards were just under 10 inches long. Two I left 3.5 inches wide and I trimmed the third to about 2.5 inches. The boards should fit snugly, but not so tight that they can’t slide in and out.

9. Cut the mitres for the top frame. This step is essentially like making a picture frame that fits over the top of the box and hides all those ugly seams. The trick is to make it slightly smaller than the inside dimensions of the box. I left about ⅛ inch of inside overhang on all four sides so I didn’t have to achieve perfect flush alignment, which is difficult with uncut wood – heck, it’s difficult with perfectly cut wood.

[Related: Every woodworker should know how to mill their own boards]

Cut the angles with a miter saw set at 45 degrees or with a miter slide on the table saw. I used the latter option because I was already working with my table saw. First I cut a 45 degree miter on one end of each board. Then I used a stop block to set the final length and cut the opposite miter for all four boards. This is a better way to ensure all four are the same length than trying to measure and mark them individually.

When all four boards are cut, glue them together with a tape clamp if you have them, or regular clamps if not, and again make sure the frame is square.

10. Glue the top frame to the box. Spread glue along the top edges of the box and align the top frame. Try to keep it square to the sides and keep the inner overhang even. Clamp the frame to allow the glue to dry.

11. Sand off any glue stains. Chances are you squeezed some glue out to clean it. Use 120 grit sandpaper in your random orbit sander and/or your hands to finish sanding any areas of the box that need it, especially around the seams. Don’t worry about the inside of the box – it will be covered with dirt or pots.

12. Insert the floor panels. Slide the base plates into place. I did not glue or nail these as they cannot fall out. This allows me to move them in the future if for some reason I need to change the depth of the box.

An empty cedar planter box on a blue rug in front of a white door inside a home.
The empty planter with the mitered top frame and bottom boards on the bottom. Jean Levasseur

13. (Optional) Line the interior with scenery fabric. Cedar is a rot-resistant wood, but rot-resistant does not mean rot-resistant. If you plan to fill the crate directly with dirt, consider putting some scenery fabric in the inside of the crate to create a barrier between the dirt and wood. Cut the landscape fabric with scissors, then staple with a staple gun.

And you are ready to plant! We plan to put existing pots in the planter box because it’s easier and quicker, but you can absolutely plant straight into the box itself – we may do that in the future.

Now all you have to do is figure out which plants will enhance your curb appeal the most. Luckily, the folks at PennState Extension have put together a guide of some best practices for container gardening. Please go out and garden.

Leave a Reply

Your email address will not be published. Required fields are marked *