How To Build DIY Window Flower Boxes (Another Workshop Project Done!)

My DIY window boxes for the workshop are done! Y’all, this might be my favorite project yet. I mean, I realize that all of these projects are working together to create the look I wanted. Had I just plopped some window boxes onto this workshop in its original state and called it good, they wouldn’t have done much for the building on their own. But of all the changes I’ve made so far, this is the one I was the most excited about. Just look how cute these are.

And I will admit that I filled them with fake plants…for now. I wanted to see what they look like filled, but it’s winter. And yes, even though I’m in central Texas, we do still kind of have a winter. It’s been getting below freezing at night, so I didn’t want to buy real plants only for them to freeze to death. So for now, the fake plants will do. Once spring hits, my plan is to turn these into self-watering planters and plant some real plants in them.

So let me show you how I built these DIY window flower boxes. This is such a simple project that pretty much anyone can do. You can see the entire process here:

To build the basic box, I used 1″ x 8″ PVC boards. After measuring my window, which was 32 inches wide, and measuring the space between shutters, which was almost 38 inches, I decided to build these boxes 34 inches wide to leave enough room for the trim that I would be adding later. So for each box, I cut one bottom piece to 32.5″, two end pieces to 7.25″, and two pieces for the front and back to 34″.

Since these are PVC boards, I used PVC glue to adhere the boards to each other and nailed the boards together with 16-gauge 1.5-inch nails. I started by attaching the ends to the bottom piece.

And once both ends were attached, it looked like this…

Then I placed the bottom/ends portion on its side, and put PVC glue on the edges of the bottom/ends, and then put more glue around the ends and bottom of the front piece. When working with PVC glue, you have to work quickly because you want the glue to be really wet when you put the pieces together. And PVC glue dries fairly quickly.

As soon as I applied a liberal amount of PVC glue to those areas, I put the front board in place and nailed it on all the way around the sides and bottom.

I repeated that process for the back piece, and then I had a very basic, no frills, plain box.

First, I trimmed out the top edge of the box using a PVC molding called shingle molding. The intended purpose of shingle molding is for use on the fascia boards of a house just under the shingles. But it’s such a pretty molding that I use it as a multi-purpose trim.

Here’s a closer look at the shingle molding…

To attach all of the trim, I used PVC glue and followed up with 18-gauge 1-inch nails. I only applied the trim to three of the four sides of the box since I needed the back to be completely flat to fit against the building. So using my miter saw, I cut the front piece mitered on both ends.

And then I cut the side pieces mitered on the front corners, and cut straight along the back edge where it would meet the building. If your mitered corners aren’t perfect, don’t worry about that. That’s what caulk and exterior wood filler are for. 😀

Here’s a look at the box with the top trim attached. You can already see how the trim really dresses up the plain box.

To trim out the bottom edge of the box, I used PVC base cap molding. The intended purpose of base cap molding is to dress up plain baseboards (i.e., to cap off plain baseboards), but again, I find myself using base cap molding for as a general purpose trim because it’s so versatile. Here’s a closer look at base cap molding…

Using my miter saw, I cut and applied that molding to the box in the same way I did the shingle molding around the top.

And with the base cap molding on, the box was really starting to look like a pretty planter.

At this point, I decided to hang these boxes on the building. And since I work alone, I had to make this as simple as possible. I went ahead and started three screws through the back of the box. I used three 3-inch exterior screws for this.

And then I held the box up in place and screwed into to the siding. This process was incredibly easy with the type of siding I have on this building. If you have stone, it’s going to take a bit more work that will require a masonry drill bit and masonry screws. And if you have lap siding, the box might need to be shimmed to get it to hang straight rather than at an angle. You’ll have to assess what you need for your particular situation.

First, I placed the corbel inside the box and marked the width of the corbel with a pencil to determine where the screws needed to be placed. And then I started four screws.

And then I used a liberal amount of PVC glue on the top of the corbel and the bottom of the box, and held the corbel in place while screwing it to the box with those four screws I started inside the box. And here’s a look at the box with both corbels attached.

And finally, I wanted to trim out the corners of the box so that the cut edges of the 1″ x 6″ boards of the box didn’t show. I used some scrap 1″ x 2″ PVC boards that I had on hand, and I cut those down using my miter saw so that I had thin strips that were 3/4″ wide and just under 1/4″ thick. If you don’t have a table saw, you can purchase thin PVC lattice or screen molding for this. And I attached these pieces vertically on the front corners and along the back where the box met the building.

And with that, the box build was done. I still need to caulk and paint (just like the skirting and the front steps) but the weather hasn’t been cooperative lately. So I’ll need to wait until we have a few sunny and dry days to do all of my caulking and painting. But I’ll be painting it all white anyway, so it won’t change the look much, if at all. But for now, I’m thoroughly enjoying the look of my uncaulked, unpainted flower boxes.

For now, I went ahead and drilled two small drainage holes on the bottom of each box. I’ll be able to fill those holes pretty easily with caulk once I get ready to convert these boxes to self-watering boxes in the spring. But for now, with all of the rain in our forecast over the next week (at least), I didn’t want these filling up with rainwater.

I just love how these turned out. I think they’re the perfect touch for my workshop, and they add some much needed dimension to the otherwise very flat building.

And while fake plants aren’t ideal, I’m happy to have them filled with something that gives some color and interest to the boxes.

I spent about $200 on fake plants for four boxes. I don’t think that’s too bad. I plan to keep them and use them each winter, if necessary. I don’t want empty window boxes. 😀 I use a combination of plants from Hobby Lobby, which I purchased during a 40% off sale, plus these from Amazon (all affiliate links): pink flower stems, boxwood stems, and weeping willow stems. Those are the ones I chose, but there are a ton of other options from that company on Amazon.

So, that’s it! Another project marked off of my list for the year. And I couldn’t be happier with how they turned out.

I did make four flower boxes so that the back windows (the windows that are visible from the street) could look cute, too. But what a mess this side looks like with that dirty skirting. But a bit part of the solution for that problem is in the works, and I’ll share that tomorrow.

For now, I just try to look past the dirt and admire my cute little window boxes. 😀