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Window flower boxes are a simple way to enhance your home’s curb appeal. These charming additions beautify your exterior while providing a perfect spot for colorful flowers, herbs, and small plants.
In the video, This Old House carpenter Nathan Gilbert demonstrates how to create eye-catching planters to add style and character to your home’s facade. Our guide describes building and installing custom window flower boxes using low-maintenance PVC materials.
Materials and Tools Needed to Build Window Flower Boxes
Before you begin your window flower box project, gather the following materials and tools:
Materials
Assorted plants and flowers
Landscape fabric
Potting soil
Tools
Building a Window Flower Box
Creating custom window flower boxes is a straightforward process that can be completed in a few hours. Follow these steps to build your own PVC window boxes.
Step 1: Measure and Cut
Measure the window sill from side to side to determine the length of each box and transfer the measurements to the 1×10 PVC boards. The box’s width should match its depth, so measure the 1×10 for its exact dimension (usually 9 ½ inches).
Using the miter saw, cut the 1×10 boards to length, using the measurements from the previous step. Each box will require a front, back, and two sides, each with corners cut at 45 degrees.
Step 3: Assemble the Pieces
Apply a bit of two-part PVC glue to the mitered faces of each corner and assemble the box. Use the brad nailer to hold the joints together while the PVC glue sets up.
Then predrill the face of the box at each mitered joint. Drive a 2 1/2-inch trimhead screw through each hole to strengthen the structure of the box.
Pro tip: Be sure to drill where the trim will hide the holes for the best look.
Measure the inside width and length of the box and cut a piece of 1×10 on the table saw to match. Glue, nail, pre-drill, and screw the bottom onto the box.
Step 4: Add Trim and Drainage
Cut the base cap and band molding on the miter saw, making sure to cut 45-degree miters at each corner. Use the brad nailer to install the band across the top of the box and the base molding across the bottom. Top the box off with 1 ¾-inch wide boards cut on the table saw, mitered at each corner.
Finally, use a ½-inch spade bit to drill weep holes every 6 to 8 inches for drainage.
Installing the Window Flower Boxes
Once your window boxes are built, it’s time to install them securely on your home’s exterior. Follow these steps for a proper installation:
- Mark the stud locations on the siding under the window. There will be studs underneath each corner of the window, as well as in the middle (check the siding for nail heads). Transfer these marks to the new window box and pre-drill holes using a ¼-inch drill bit.
- Hold the box in place and mark the hole locations on the siding with a pencil. Remove the box and pre-drill the holes before squeezing a dab of caulk into each hole.
- Hold the flower box back up and use the right-angle attachment to drive 4-inch structural screws from inside the box into the wall framing.
Window Flower Box: Planting and Maintenance
With your window boxes securely installed, it’s time to add some greenery. Landscape contractor Jenn Nawada offers valuable plant selection and care insights in the video above. Here are some tips for planting and maintaining your window boxes:
Choosing Plants
Select a mix of plants that thrive in the light conditions of your window boxes. Consider:
- Perennials for long-term growth
- Annuals for seasonal color
- Trailing plants for cascading effects
Once you’ve selected the plants you’d like:
- Line the planter with landscape fabric to prevent soil from escaping through drainage holes.
- Add a 1-inch layer of volcanic lava rock to improve drainage.
- Fill the box with high-quality potting soil, leaving room for your plants.
- Arrange your chosen plants, ensuring a mix of heights and textures.
- Gently remove plants from their containers and loosen the root balls before planting.
- Fill in around the plants with additional potting soil and water thoroughly.
Ongoing Care
To keep your window boxes looking their best, water regularly, especially during hot, dry periods.
Apply a slow-release fertilizer every three months to promote healthy growth, and prune and deadhead plants as needed to maintain shape and encourage blooming. Replace seasonal plants as needed to maintain year-round interest
Resources
Gilbert used stock 1″x10″ Azek and stock Azek band molding and base cap molding to build three identical window boxes. To cut the materials to size, Gilbert used a sliding compound miter saw manufactured by Dewalt. To secure the front, back, bottom, and side pieces together, Gilbert used 2-part PVC glue, 1 1/4-inch brads, and 2 ½ -inch stainless steel trim head screws, which can all be found at home centers. He secured the molding with 2-part PVC glue and 1-inch brads. To allow for drainage, Gilbert created drainage holes on the bottom of the window boxes. He used a 1/2-inch spade bit to drill holes every 8 inches along the centerline of the bottom piece of Azek.
Gilbert mounted each window box directly to the house’s siding. He pre-drilled pilot holes, added caulk into each hole, then used 4-inch structural screws to secure the box to the clapboard through the pre-drilled holes.
Nawada lined the window boxes with one layer of landscape fabric, which can be found at garden and home centers. On top of the landscape fabric, she added handfuls of Volcanic Lava Rock to cover the drainage holes. Nawada used a combination of annuals and perennials to fill the window boxes, which get morning sun and afternoon shade. Plants and flowers used include Northern Maidenhair Ferns, Pearly White, Glacier Ivy, begonia, bush violet, and vinca, which she planted in Fox Farm Ocean Forest potting soil made by Fox Farm. In addition to regular watering, Nawada suggests using a slow-release fertilizer like Osmocote—made by Scotts Company—once every three months to help keep the window boxes healthy.
