How to Build a Window Planter Box From Cedar

A window planter is a great addition to the outside of your house and a fun way to add some color and life to your windows. We recently added window planters made from bargain cedar to all of our exterior windows. Follow along to see how we built them!


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All dimensions for the build are based on the planter container that the cedar box will be built around. We actually bought a size too small to match our window for this build, so make sure and measure your window to figure out your size BEFORE you start building….


The first step is to build the frame of the box. I was able to find some cedar fence planks in the bargain pile at my local big box store. I took these to the table saw and ripped them down to a thickness of 1 in. If you don’t have a table saw you can easily make this cut with a circular saw and straight edge (like a 2x4)!


I then measured the dimensions of my planter insert and cut the base frame to size. Be sure and increase your dimensions by 1 in for both the width and length to account for the pickets that will be attached to the inside at a later step. This step is duplicated to have 2 frames, one for the top and one for the bottom.


The frame was attached with wood glue and brad nails. You could just use wood glue and clamps but the nails allowed me to take the frame out of the clamps and keep working.


Next up are the wooden pickets. These are cut down to size to leave a 1/2” gap at the bottom and a 1/4” gap at the top of the project once the entire frame has been put together. This will allow for the base to be inserted as well as the top lip of the flower container to extend beyond the frame.


One picket is cut down to a smaller size so that everything will fit snug. I split the difference into both sides so that everything would be symmetrical.

These are attached with glue and brad nails.


The vertical supports are then cut and glue/nailed into place. You could miter the edges of these to make for a more even look. For this project, I just butted them against each other at the corners.


The top frame is then glued and nailed, this sits on top of the vertical supports and is attached to the interior pickets.


Now, the only thing we are missing is a bottom! I measured the width of the bottom and then cut two pickets so they would be equal in size. I then glued and nailed it into place.


The next step is everyone’s favorite…sanding!


I initially thought this would be the end of the project but after showing it to my wife she had a great idea on how we could hide the top of the planter insert by make a quick and easy lip!


I made a strip of wood that was the same width as the pieces used for the frame. The lip will not go along the back since this will be against my house. When cutting miters I’ve found it easier to cut them all to size as you work your way around a project. So I started with one of the sides and cut the miter so that it extended beyond the frame of the box. These were cut a 45º angle with a miter saw.


The entire lip was attached with…you guessed it, glue and brad nails! Everything was given a final sand and I applied a coat of spray outdoor Polyurethane to protect it.


With the entire planter done and the insert inside it was time to mount it underneath a window! I first drilled a scrap piece of a picket to the wall. This is measured so that it will fit inside the back frame. Since this piece of wood is the same thickness as the frame the planter will sit flush.


I then placed the planter against the board and drilled two 3” decking screws from the inside of the planter into the mounting board and our exterior wall. I had to purchase a right angle drill attachment so I could get at the “right” angle!


And that’s it! Since our this was mounted below our kitchen window all we have to do is reach out and grab an herb while we are cooking!

Brandon Cullum