How to Build a Window Box

Last week, we touched base on my 2020 home goals. On that list, I included the task of building a new front window box for the outside of our home. While I loved the one that was there when we moved in, it was rotting and looking a tad weathered. Take a look for yourself…Our old window box rotting

I figured this couldn’t be that difficult of a DIY project, so Finn and I spent the 4th of July weekend building it! You can watch all of the behind-the-scenes from this project on Instagram stories right here. How to build a front window boxIn fact, I would say it was actually pretty easy and I’m confident each and every one of you could build your own window box too!

Window Box SuppliesWood used to build a window box

First, gather all of your supplies. We headed to the hardware store (with masks on, of course!) and got all of our wood and paint. We used cedar for the box because it’s a great wood to use outdoors. Also, be sure to buy primer, paint, and wood screws that are specifically made for exterior use. You want this window box to last for a long time!

How to Build a Window BoxHow to build a window box

We did our best to mimic the old window box in terms of size. Our old one was super long at 8 feet, so we did the same with the new one. We ended up using 8-inch boards for the front and back and 6-inch boards for the bottom and sides. If I could go back in time, I would have just used 8-inch everywhere because we had a tough time squeezing our plants in (more on that below!). Cut your wood for your DIY window box

Even though we ended up buying the wood from the hardware store at 8 feet already, we measured them all and realized they were off a little bit here and there. We ended up cutting a tiny bit off to make them all exactly the same. You want them to be as uniform as possible as it will make building the box a lot easier!

Build the BoxUsing a corner clamp to hold two pieces of wood together

With our wood cut, we used corner clamps and regular clamps to hold the back and bottom together. These corner clamps are sooooo handy because they keep that perfect right angle. I highly recommend picking these up (we first got them for our DIY built-in project and now use them anytime we build just about anything). Power pro hardware screws

I then used these PowerPro wood screws to attach the back and bottom together. These are great because you don’t have to drill a pilot hole first! Instead, these just go in like butter. I wish I knew about these a long time ago! Just like the clamps, these are a must for any building project. Measure for the sides

With the two pieces together, we measured for the two side pieces and screwed those in from the bottom and the back. How to build a window box

We added the front piece on…again screwing it directly onto the other pieces of wood. Since this is a planter box, you’ll want to add drainage holes to the bottom. I used a 1/2 inch drill bit and made several holes along the bottom with my drill.

Add Decorative TrimHow to add trim to a custom window box

I wanted the trim to have a clean Craftsman-style look, so we used 1×2 pine for that.  Not only does trim add a decorative detail, but it also hides the seams of the wood. We ended up making boxes on each side and two boxes on the front. We kept the back of the window box bare. How to add decorative trim to a window box

exterior wood glueTo attach the trim, I used exterior wood glue and a brad nailer with 1.5-inch finishing nails. Those suckers weren’t going anywhere!

Fill Holes and SandUse wood filler when you're building window boxes to make it look more polished

It is always a good idea to use wood filler in order to make everything look uniform and to hide screw and nail holes. We used a spatula to spread it over holes, seams, and any other imperfection. Once it dried, we sanded it and also gave the entire box a good sanding with our palm sander. You’ll want it to be smooth to the touch so it takes the paint really well.

Prime & PaintKilz mold and mildew primer

I used some of the leftover mold & mildew primer from my bathroom project to coat the entire box with a primer. This not only helps the paint adhere better, but it should also prevent moisture problems down the line. Fingers crossed. Behr exterior paint

Once the primer dried (about an hour later), I gave the entire box two coats of paint. I used an exterior paint from Behr in their regular “Pure White” in a satin finish. Painting a window box

So fresh and clean looking!

Transporting the Plants

Putting plants in our window box

Here’s where I ran into a small snafu. In our old planter box, I planted all of our flowers in three plastic inserts that I placed directly into the wood flower box. This made clean-up easy and protected the box a bit. When I took those plastic inserts out to place into the new box, I realized that we didn’t make the new window box wide enough. Oops. Somehow I must have measured incorrectly (palm to forehead) and they didn’t fit.  As I mentioned earlier, I should have made the box a tad wider. So definitely consider that if you’re planning to use plastic trays in your window box. How to plant in a window box

I ended up just removing the flowers from the plastic inserts and putting them directly into the box. This worked out great! A few followers recommended putting mesh or some sort of plastic on the bottom of the box so it lasts longer. I’ll have to try that out next year.

Our New Window BoxOur new window box

How to build a window box
How to build a front window box

I am so pleased with how our new window box turned out. Even though it looks very similar to our old one, this one is fresh, new, and upgraded. Plus, now I know that it should last for years and years. I thought the plants might drop right through that old one at any time. Ha!

A few people asked how we attached it to the brick. The ledges that it rests on were already there when we purchased the house, so we just rest it on top of those and don’t attach it at all. The weight keeps it from budging. If you don’t have ledges to rest your window box on, you could drill L-brackets into the brick so it rests on those. Here’s a good tutorial showing that. Flowers in our window box

As I discussed in this post, I planted spikes, vinca vines, white wave petunias, and sweet potato vines in here at the beginning of the summer. They’re all still thriving! How to build a window box

Rory seemed unimpressed with our new build. Maybe next year she will be able to “help” her mama plant the flowers up here.

How to build a window box

Now, go out and build a window box! I promise it will boost your curb appeal in a weekend.


The Year of Casey

Hey there!

I’m Casey Finn, the voice behind The DIY Playbook. I’m a Chicago gal teaching you how to design, DIY, and maintain your home…by yourself! Learn more about me right here.

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