How to Build a Gorgeous DIY Hanging Window Box Planter

Do you want to learn how to make your own window boxes? Let me show you how to add instant curb appeal to your home in just an afternoon!

This post is sponsored by Lowe’s Home Improvement Stores and contains affiliate links, however all opinions and recommendations are my own. Please see my full disclosure policy for more details.

Window planter boxes are a great way to elevate the look of your home by adding eye catching beautiful flowers. They’re inexpensive, easy to make and can be created in a number of different designs to coordinate with the style and architecture of your home.

This is a project I’ve dreamed of adding to the front of our very traditional brick home for years now. But I

was intimidated at the thought of making my own. It turns out, these basic boxes aren’t very hard to construct with the right tools.

So, let’s break down exactly how I made my own DIY window flower box.

Materials

While designs may vary, this list includes the basic, essential materials you’ll need to make any DIY window planter box.

Wood glue
wood filler
Plastic Planter Box Insert
3/4″ Pine Plywood (I purchased this 4’x8′ sheet from Lowe’s)
(3) 1×2 pine boards in 8′ length
(2) Wooden Corbels
Exterior Paint
Potting Mix & Flowers

*A note about selecting the right wood for this project. You can also opt for scrap wood or cedar boards, but make sure that you use the proper exterior paint to seal your window boxes to prevent rot. I chose the WeatherShield line from HGTV Home by Sherwin Williams specifically for its outdoor protection.

Tools

While these are the specific tools I used for the project, you don’t necessarily need all of these to make your cuts. Lowe’s is perfectly happy to rip down your plywood into smaller, more manageable pieces for you.

And if power saws just aren’t your jam, you can also use a simple miter box and hand saw to trim down your pieces once you get them home.

How to make window flower boxes the easy way

I built this wooden window box specifically to fit the dimensions of these inexpensive planter inserts. I loved the idea of being able to take the entire insert out to change out my plants and flowers from season to season.

Our windows are 36″ wide and they fit the width of the window perfectly, but should you need a smaller size, they also came in 24″. You’ll just need to adjust your wood cuts to account for this.

Step 1 – Make your Cuts

The first thing you want to do before building your boxes is to make all of your plywood cuts for the assembly. I’m going to list them out for you here, but I’ve also included a picture below so that you can visualize how the boards will fit together.

(1) 9″ x 36″ piece for the bottom board
(2) 9″ x 7″ pieces for the side boards
(2) 7″ x 37 3/16″ pieces for the front and back boards

Step 2 – Drill Pocket Holes

Next, you’ll want to drill your pocket holes to assemble the pieces together. Starting with your bottom board, drill holes along each side as pictured below. I chose to do double pocket holes, which may have been a tad overkill, but I wanted to be sure the base could withstand the weight of the heavy soil and inserts.

Spoiler alert, you’ll be fine just drilling single pocket holes if you’d like.

Then you’ll drill pocket holes on one side of each of your side boards as below.

Both the front and back boards won’t have any holes in them.

Step 3 – Assemble the Box

The first thing you want to do is add a thin layer of glue to the sides of either of the long ends.

Next, you’ll lay it perpendicular on top of the front board so that it sits directly in the center of the bottom of that piece as shown below.

Using your pocket hole screws, begin attaching these two pieces together, being sure to press firmly as you drill to ensure a tight fit.

Then, you’ll attach each side piece in the same manner. Be sure to add wood glue to all edges before inserting your pocket screws.

Lastly, you’ll attach your back board.

You’ll notice that because of the shallow depth of the box, we can’t use pocket screws to attach the side pieces to this back board, so we’ll be using wood screws to attach it instead,

Start by drilling three small pilot holes along the sides of the board. This will help to avoid the wood from splitting when you attach the screws.

Finally, attach the wood screws ensuring a tight fit to the side boards.

Step 4 – Sand the Box

I made the mistake of skipping this step initially and it resulted in a very poor paint job, so I’d recommend taking a few minutes to go over the exterior of your boxes with 120 grit sandpaper to knock down their rough texture a bit.

You can then give them a final pass with 220 grit to smooth them out and prepare them for painting. It’s much easier to sand them before adding the trim pieces rather than after.

Step 5 – Cut Trim pieces

The best way to personalize these DIY window boxes is by adding trim pieces or boards. I chose these simple 1″ x 4″ boards to line the top and bottom of my boxes.

I used my miter saw to cut 45 degree angles to join the front corners together while the back side edges were flat 90 degree cuts to sit flush with the back of the box.

All pieces are going to be the same lengths as your fronts and sides, but I would recommend measuring after you’ve assembled the box to account for any movement before you make your cuts.

Step 6 – Attach Trim pieces

Add a thin layer of glue to the backs of all of your trim pieces before securing them with your brad nailer. Use 1″ brad nails to secure the pieces in place.

Once you’ve attached your trim, you can add a thin bead of caulk along any open seams and fill all nail holes with nail filler before sanding.

I found that the wood filler worked perfectly to fill in the gaps of my open mitered edges where my measurements may have been slightly off as well.

Step 7 – Create Drainage Holes

This is the most important thing, because you need to create proper drainage to allow for excess water to be removed from the soil.

The first step is to drill large enough holes in the bottom of the planter insert.

Next you can place your insert in the box and mark the holes you just created. This will ensure your drainage holes line up correctly.

Once you’ve marked them you can create your corresponding holes in the bottom of the box.

I recommend drilling these holes slightly larger than the planter holes to avoid any standing water in the bottom of the window boxes.

Step 8 – Attach Corbels

Lay your window box on a flat surface on its back side with the front facing up. Measure 7″ inward from each side of the box and make a mark with pencil. This will be the point where you attach the edge of the corbels.

Add a thin layer of wood glue to the side of the corbel that does not have the built-in metal bracket. This is because you’ll need the brad nails to be able to go through and attach the corbel without the metal bracket in the way.

Attach the corbel with wood glue to the bottom of the window boxes by making sure that the back sits flush with the back board of the window box.

Next, secure the corbel with 1.5″ brad nails to the base of the box. You’ll notice this only reaches the tip of the corbel, and because of its deep curved shape, you’ll need to continue securing it from the inside of the window box as well.

An additional three to four nails from the inside should be more than enough to hold it tightly in place.

This is only a decorative piece to add visual interest and not meant to be weight bearing.

Now you’re finished adding the finishing touches to your window boxes and they’re ready for paint!

Step 9 – Paint your window box

Lastly, you’re going to add 3-4 coats of paint to your new window boxes. I always like to use my paint sprayers for the best finish possible and this Wagner Flexio happens to be on sale right now at Lowe’s.

I mentioned earlier that you want to select a good quality exterior paint for this project to prevent the wood from rotting and maintain your beautiful boxes. That’s why I chose the WeatherShield line from HGTV by Sherwin Williams specifically for this project.

I chose the color Natural Choice to complement our existing exterior trim and to add a pop of contrast against our dark red brick, and I think it looks absolutely perfect.

The satin sheen feels smooth to the touch and hides any visible imperfections in the wood as well.

How Do you Attach a Planter Box to a Window Sill?

There are several ways you can attach window boxes to the exterior of your home, but for our project, we chose to use simple masonry screws and anchors.

We placed the boxes just beneath our brick sill and marked the position of our holes using a regular drill bit. We staggered four screws in the back of each window box and they’re holding incredibly strong.

I would suggest using a hammer drill to create the holes in your brick as you’ll very easily drain the battery in a standard drill attempting to do this.

If you have vinyl siding or choose to use metal brackets to attach them to the side of your house, I’d recommend checking with your Lowe’s local Hardware Store to find out what they suggest using.

Their team was incredibly helpful when I had no idea what to select.

I’m so incredibly proud of this easy DIY window box planter! I filled it with some colorful flowers and just love how it updated the front of our home.