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Window Planter Box Plans: How to Build a Window Box

Our cottage garden shed with its new window box planter.

Our cottage garden shed with its new window box planter.

Add Visual Interest With a Window Box!

Our shed looked pretty good. We painted it gray with white trim to match our house, added a custom-built birdhouse cupola to the roof, planted some shrubs around its base, and hung a few other signs and other decorations—including a moose antler. To complete the transition from a bland storage shack into an attractive cottage garden shed, we wanted to add a window box.

What Is the Purpose of a Window Box?

A window box filled with colorful annuals, interesting foliage plants, and edible herbs is an attractive addition to the facade of nearly any building. Many options and styles exist, so you can pick one to fit almost every window, deck, or railing. Traditional planter boxes are often made from redwood, cedar, or pine. The styles range from a basic utilitarian rectangular box to ornate Victorian window accessories. A variety of window planters are also offered in metal, plastic, and composites.

Finding a planting box that fit the window in the shed was more difficult than I expected, so I decided to build my own. Building a custom window planter box is an easy DIY woodworking project that can be completed in just a few hours. I made ours from inexpensive pine board, a leftover piece of plywood, and a few bits from the scrap box.

We then filled the finished window box with annual flowers. After the summer blooms fade and the seasons change, we swap out the spent flowers for decorative winter berries and greens. The little cottage garden shed now looks right at home in our backyard landscape.

Do you want to build one for yourself? Let's get started!

Coleus and petunias in our window planter box

Coleus and petunias in our window planter box

How to Build a Window Planter Box

The Cutting List:

  • Front (A): 31"L x 7"W
  • Sides (B): 6-3/4"L x 7"W
  • Back (C): 31"L x 7"W
  • Bottom (D): 29-1/2"L x 6"W


  1. Begin your project by measuring the width of your window. On our backyard shed, the window is 24" wide. The planter spans the width of the window plus the trim on either side, bringing the total length of my window box to 31" long.
  2. We designed our planter to hold 6" nursery pots, so the interior of the box measures 6" wide. The length of each piece of stock was cut according to the cutting list and assembled following to the window box planter plans diagram (below). Before you make any cuts to your lumber, adjust the measurement of each piece to fit your window.
  3. The bottom of the planter was cut from a scrap of exterior grade plywood and sized to fit the inside opening of the box. Supported by cleats tacked around the base of the interior, the bottom section is removable for easy cleaning and re-potting. Drilling a few holes through the bottom provides drainage.
  4. To add a little style to this simple box, I added thin pieces of trim around the perimeter of the front section. Another section of trim divides the center of the front panel. It is much easier to paint the trim pieces before attaching them to contrast against the gray paint of the planter and match the trim around the window and door.

Window Planter Box Plans:

Window Box Planter Plans

Window Box Planter Plans

How to Assemble the Window Planter

Assembling the window box is straightforward and uses a combination of weather-resistant nails or screws together with exterior grade glue. Attach the sides (Part B) to the back section (Part C), taking care to position the back section between the side pieces.

  1. Position the front section (Part A) across the two side pieces. Secure the pieces with glue and screws or nails. Check to ensure that the planter box is 'square' and each corner measures 90 degrees. Measure and cut the bottom section to fit inside the window box. For my planter, the bottom pieces measure 29-1/2" long by 6" wide. The bottom section is not secured to the planter box. Instead, the bottom piece rests on 3/4" x 3/4" cleats that are attached to the interior of the planter. Measure and cut the cleats to fit, and then attach the cleats with nails or screws.
  2. Paint the inside and outside of the window box with a quality exterior grade paint. Now is a good time to paint the trim too, before the trim is applied to the front section of the planter.
  3. The trim pieces were cut from a thin strip of wood that measures 3/4" wide by 1/4" thick. Measure and cut two pieces of trim to run laterally across the top and bottom of the front section (mine are 29-1/2" long) and attach using small nails. Then, measure and cut the upright trim pieces and attach with a few more nails. It's time to hang your window box and add the plants!
Cleat Hanging System

Cleat Hanging System

A Cleat Hanging System

I use a simple cleat system for hanging projects such as birdhouses and this window box. The cleat is made by ripping a scrap piece of stock at a 45° angle. As shown in the diagram, one piece is attached to the window box and locks into the second piece, which is attached to the garden shed.

  1. To make the hanging cleat, start with a piece of wood that is at least four inches wide, and slightly shorter than the length of the window box.
  2. Tilt the table saw blade to 45 degrees, then set the fence to 2 " from the blade to rip the stock into two mirror-image pieces, each with a 45-degree bevel cut along one edge. When ripped at a 45-degree bevel, the 4-inch wide piece of stock will yield two mirror image cleats that measure approximately 2 " on the wide side.
  3. One cleat is attached to the back of the project with the 45-degree angle of the cleat pointing downward, forming an inverted "V" between the back of the box and the outside surface of the cleat.
  4. Attach the second cleat where you want to hang the planter, this time with the "V" of the cleat facing upward. Use weather-resistant screws, and make sure the cleat is level.
  5. When fitted together, the two 45-degree "V"s from each piece lock together to securely hold the window box in place.
  6. Adding a filler strip along the bottom edge of the window box below the cleat on the backside will hold the planter level upright and plumb. Cut the filler strip to the same thickness as the cleats.

Window Box Container Gardening

The New Window Planter Box Looks Great!

The New Window Planter Box Looks Great!

Do You Have A Window Box?

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2012 Anthony Altorenna

Tell Us About Your Window Boxes

Rosaquid on June 27, 2012:

Thanks for the clear, inspiring instructions! I love window boxes.

Renaissance Woman from Colorado on June 17, 2012:

Beautiful window box and love your shed, too. I think window boxes are one of my very favorite things about the outside of my cabin (along with rustic shutters). Geraniums are my window box flower of choice. There is just something so happy about them. Thanks for another wonderful project tutorial. Happy Father's Day!

tutors091 on June 17, 2012:

Great, a lot of good content to get started on window planters.

Spikey64 on June 17, 2012:

Great lens. I am thinking of building a window box to put under the kitchen window.I intend to grow a selection of herbs so I can just reach out of the window to get them when I am cooking. You can't get much fresher than that.

MariePalmer LM on June 16, 2012:

I love window boxes, I use mine for herbs right now. I tweeted this lens for you.

purpleslug on June 16, 2012:

I love window boxes, they add so much to your home. Great lens! Thanks!

anonymous on June 16, 2012:

I really like this lens. Thanks for including window box planter plan.

Michey LM on June 15, 2012:

Very nice and well explained, I like windows box with beautiful flowers, it chanded the entire appearance of the house.

anonymous on June 15, 2012:

Good plans. Not allowed to have a window box by the association of our complex but still enjoyed reading this article.

Tea Pixie on June 15, 2012:

I LOVE the information you have given - it is so easy to understand and seems reasonable to complete. I am often befuddled by instructions - unless they are well written. You have done a wonderful job here.

peggygallyot on June 15, 2012:

I love this lens.always wanted a window box planter

Lareene from Atlanta, GA on June 14, 2012:

I love this lens the flower boxes are so cute thanks.

CCTVwebmaster on June 13, 2012:

Brilliant lens, I will definitely give this a go, always wanted window boxes but never tried to make one myself.

allenwebstarme on June 13, 2012:

Such a great idea, window box planter looking great.

Mary Norton from Ontario, Canada on June 12, 2012:

How good of you to share this how to. Love window boxes especially the wooden ones.

deckdesign on June 11, 2012:

I'm almost finished building my new garden shed and I think a window box planter will look good under the front window. I think I have my next project. Thanks for providing instructions and details to build it.

Rose Jones on June 11, 2012:

This reminds me of a story I read in Readers Digest about the Miracle of the Window Box. It concerned a young couple who bought into a rough neighborhood, and had their window box ripped off. Undaunted, they involved the community in making window boxes: having a contest, supplying the materials - and the beauty transformed the neighborhood.

Ellen Gregory from Connecticut, USA on June 11, 2012:

Very nice lens. Nice of you to share your windowbox plans

Karnel from Lower Mainland of BC on June 11, 2012:

I am a huge fan of window boxes, well done and congrats for being on the front page.

IMKZRNU2 from Pacific Northwest on June 10, 2012:

I love window boxes. They add so much to the front of a house. Thanks for sharing this lens!

BeyondRoses on June 10, 2012:

I don't have a window box container, but would love to have one. Creative you!

Gayle Dowell from Kansas on June 10, 2012:

I bought blueprint plans from the local extension office years ago to build a window box. That was at least 20 years ago. I still want one. I'll have to dig out the plans and get to work.

pawpaw911 on June 10, 2012:

When I saw the "how to" title, I thought of you, and sure enough, it was your lens. Another excellent how to lens. Might have to give this window box a try, if I ever get a few less irons in the fire.

jlshernandez on June 10, 2012:

Another wonderful DIY lens on window boxes. I have always wanted one but did not know how to suspend them and irrigate the plants.

Indigo Janson from UK on June 10, 2012:

I adore window boxes. Don't know why I don't have one but I think it's time I changed that. Thanks for sharing such a great tutorial!

Natural_Skin_Care on June 10, 2012:

Window planters make such a nice finishing touch. Nothing like that pop of color.