How To Build A Window Box

April 21, 2022

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In 2018, I had the idea of putting a window planter box in front of my house. But when I started shopping online, I was totally shocked by how expensive they were. $70 for ONE window box?!

I barely had $70 to spare, let alone double–so it was a pretty easy decision to make a DIY window box myself. 

This is an updated post from a project done in 2018. This was the FIRST THING I ever built! I had very little DIY knowledge, very little money, but just enough determination. The pictures are sub-par, but if there was ever a truly easy DIY project that ANYONE can do with just basic tools, this is it.

But yall, I literally didn’t own a saw. I knew how to push a button on my drill, and that’s basically all I needed for this. You can absolutely do this project, and you can make it fancier and prettier than I did, too.

DIY Window Box Supplies & Materials

To make your DIY window box as easy as possible, I’ve attached links to the materials on both Home Depot and Lowe’s. Both stores offer online ordering and usually do same-day pickup. 

Window Box Planter Supplies & Materials – Method 1

Important note: There are multiple different ways to build your own window box, so I’m going to cover the top two in this article. The first method is the original steps I followed in 2018, and you only need basic materials for that one. The second method is what I’d use today. They differ in step 5, so you can see the differences there.

Window Box Planter Supplies & Materials – Method 2

I am not including any saws in this list, because you can just get these boards cut at the hardware store for free. With a miter saw, you can make all of these cuts pretty much instantly. You can also cut a straight line with jigsaw or circular saw.

Step 1: Measure & Cut Your Wood

You’ll have to decide how wide and deep you want your boxes to be before deciding on which wood to buy. I wanted my boxes to be about the same width as my windows, which was 32 inches wide. I also chose to make it 6 inches deep, so those are the measurements I’ll reference.

However, I made my 2022 window box out of two of these fence panels I found in my garage. They measure 1×4, and are under $2. So yeah–YOU CAN MAKE A WINDOW BOX FOR LESS THAN $4.

Now, for each window box, you needed three pieces cut to length (i.ei. 32 inches). These will become the bottom of the box, the front, and the back.

DIY window box planter wood

Then you’ll need to calculate the side pieces. You could do this part differently if you choose, but I believe it’s easiest to cut squares of wood that fit inside of your front and back pieces, like this:

DIY window boxes tip for attaching wood

This means you’ll need to make a piece that’s a little bit shorter and a little bit thinner than the wood you’re using–but it’s not difficult to calculate. In fact, you can take a piece of paper or scrap wood to cut the right size, then just trace that on your wood before you cut.

Super easy way to connect wood for DIY planter boxes

How to calculate wood cuts for diy window boxes

You could also use pure math… but who wants to do that?! Especially since most wood is not perfectly measured. 1x6s are usually actually about 5.5 inches…. Just, ya know, avoid math, okay?

Step 2: Prep Your Wood

In this project, the main step to prepping your wood is just sanding.

Of course I didn’t have a sander in 2018, so I just used sandpaper or a sanding block. Now I have an orbital sander, but it’s this $16 one from Walmart. Honestly, it’s been all I’ve needed for over a year.

Using a sander on your wood before you begin takes about 4 minutes. I don’t know why everyone likes to hate on sanding so much, it’s not that bad.

You could also choose to paint or stain your pieces now, before assembly. For staining, it would be much easier at this point.

But for more details on finishing your wood, go to step 6.

Step 3: Fit Wood Pieces Together

Now, the next step will take approximately 30 seconds in practice, but it’s still important enough to mention.

How to build a window box, three sides

With your three wood pieces, fit them together the way that your window box will sit. Look for any significant gaps, and switch the wood pieces around until they all fit evenly and any “pretty” pieces are on the front.

This step is important, especially if this is one of your first projects like it was mine. MOST wood in Lowe’s or Home Depot is far from perfect, and a lot of is bowed or cupped.

To avoid this, you should look through the wood pieces in the store to find the straightest pieces. However, it’s still not perfect. And if you didn’t do that–IT’S OKAY! For this project, you will most likely be fine.

You can read much more about how to find straight wood and WHY it’s so important in the “mistakes” section of my article on how to wrap porch posts.

Step 4: Apply Wood Glue and Clamp the Pieces

Once you have your boards in position, it’s ideal to use wood glue to put them together and then add clamps.

I did not do this step in 2018 because I didn’t think it was important–and it could be done without. However, wood glue is a gift from Heaven, okay? It’s like insanely powerful. When in doubt, use wood glue.

I also did not use clamps in 2018, but that is just WRONG. Regardless of which window box method you use, clamps make it so much easier. Without clamps, the board will absolutely-without-a-doubt-100% move around as you’re trying to drill or nail.

tools and materials to build window planter box

So just use clamps, okay? Bar clamps will change your life.

Step 5: Attach Boards to Each Other

This is where there are two different methods. Both are extremely simple. Basically, method #1 uses a drill and pilot holes, and method #2 uses a nail gun. Read on for the details.

Method 1: Drill Pilot Holes + Add Screws

With your clamps on, use a small drill bit to drill pilot holes along the front and back of your window box pieces.

Build a DIY window box planter

If you don’t use clamps OR wood glue, like I didn’t originally, you can just add the pilot holes and then the screws to one board at a time. You’ll start with an L-shape like the picture below, then add the third piece.

Window planter tutorial for home's exterior

2018 Kaylee only did these projects with a baby monitor on full volume… but usually my baby would wake up anyway because he couldn’t be more than 3 feet away from me for the first 18 months of his life.

He was SO cute, so I was okay with it. 😉

Window box tutorial

Cutest picture of a drill EVER, right?! 😉

(And no, he didn’t get into the drill bits. I know they’re laying right there and you’re worried about it. But fear not, no babies were harmed in the making of these boxes.)

Don’t forget to then add your side pieces and drill into those from the front, back, and maybe even the bottom.

Method 2: Nail Gun + Brad Nails

If you have a nail gun already and your boards are glued and clamps, this step is literally just adding nails.

Nail gun building window boxes

I mean… that’s it. That’s just all there is. 

Step 6: Paint or Stain the Window Boxes

And suddenly–YOU HAVE A WINDOW BOX!

DIY Window box result

Now it’s time to stain or paint the planter box if you haven’t already.

Since these are going to be outside, you need to make sure you use a the right products for exterior use. Check if your stain includes an exterior sealer, and use exterior paint.

In my original window box, I used black spray paint. If you do that, I prefer the High Performance Enamel.

As with all spray paint projects, start with a light coat instead of trying to get coverage immediately.

Painted window box

Step 7: Add Drainage Holes

The last step of building your window box planter–other than actually putting in flowers–is to add drainage holes on the bottom.

This is as easy as taking the largest drill bit you have and drilling holes in the bottom board.

Drainage holes in window box

Step 8: Install and Add Flowers

I have detailed instructions to attach window boxes to siding, so make sure you read that to make installation easy.

Finally, it’s time to customize your box with beautiful flowers! There are so many different planter box ideas that can really spruce up your space.

Window boxes are fun because you can make them beautiful and festive all year round! Here are 11 Fall windox box ideas I gathered.

Again, I come to you apologetic about the quality of my 2018 pictures. This is the after picture I took *facepalm*:

DIY window boxes result

This simple window box should take you a maximum of about 40 minutes–and then it’s an instant boost to your curb appeal.

In the house pictured above, I also did these exterior DIY projects: 

In 2022, I’m currently working on limewashing my brick, building shutters, building an exterior bench, and completely landscaping a courtyard from scratch.

There will be lost of mistakes, learning, and me squealing–follow along on TikTok or Instagram.

DIY window box


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Hi! I’m Kaylee–a mom of 2, business owner, DIY addict, and so much more. You’ll find some fun DIY tutorials, totally honest reviews, and lots of tips for making your home fit YOU. Welcome to Mama and More!

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