How to Build a Window Box

Window boxes are a cheerful way to add plants to any room -- or to the exterior of your home. This sturdy, simple box is ideal for a wide variety of window-dwelling plants.

Tools:
  • measuring rule
  • pencil
  • carpenters' square
  • handsaw or power saw
  • small mixing dish and stick
  • power drill with 11/64-inch, 1/2-inch, and carbide-tipped bits
  • screwdriver
  • hammer
  • safety goggles
Materials:
  • 1 × 2 and 1 × 8, 1 × 10, or 1 × 12 redwood or cedar stock
  • resorcinol glue
  • #8 × 1 1/4-inch brass or stainless steel flathead wood screws
  • 6-penny brass or stainless steel finishing nails
  • heavy-duty shelf brackets
  • #8 × 2-inch brass or stainless steel flathead screws, or 2-inch lag screws with lead masonry anchors
Time: about 1 to 1 1/2 hours.

You should plan to build your window box to the full inside width of the window. Use 1 × 8, 1 × 10, or 1 × 12 redwood or cedar boards for the box width and depth desired. The finished window box will be as wide and as deep as the boards you use.

Make your windowbox from boards of the depth and width desired; add reinforcing strips around the top.
Use 1 × 8, 1 × 10, or 1 × 12 boards for the depth and width desired;
add 1 × 2 reinforcing strips around the top edge of the box.
Cut the front and back to the inside width of the window frame.

To make the box, measure across the inside of the window frame. If you work from this measurement, the finished window box will be about 1 1/2 inches wider than the window on each side; adjust this width if you would like to make the box narrower or wider. Using a carpenters' square to keep the ends straight, measure and mark three boards to the desired length of the box; then cut them with a handsaw or a power saw. For each of the two side pieces, measure and cut a piece of board as long as the width of the stock, plus 1 1/2 inches.

Put the pieces together with simple butt joints, with the front and back of the box butted over the bottom and all board edges flush. Set the side pieces directly over the open ends of the box, with the grain of the side pieces running the same way as the grain of the front and back, so that the pattern of the wood wraps around the box.

Next you'll fasten the box together with resorcinol glue and #8 × 1 1/4-inch brass or stainless steel flathead wood screws. First, attach the front and back boards to the bottom board and then secure the side pieces. For each joint, drill 11/64-inch holes through the face of the board being attached -- the front and back boards and the side pieces, but not the bottom board. Drill holes at each end of the board and about every 4 inches all along the joint line, set back about 3/8 inch from the edge of the board. Set the board into place, mark the screw holes on the board edge it's being fastened to, and drill starter holes into the board edge at the marked points.

Mix resorcinol glue as directed by the manufacturer. Apply glue to the edge of the board you're fastening to and set the facing board into place against the glued edge, with all board edges flush. Secure the joint with # 8 × 1 1/4-inch brass or stainless steel flathead wood screws through the predrilled holes and into the edge board.

For a stronger window box, add a reinforcing strip across the front and around the sides, and butt the front strip over the cut ends of the two side strips. Measure and cut strips of 1 × 2 redwood or cedar for this reinforcing band. First attach the side strips and then the front strip, with the top edge of the 1 × 2s flush with the top of the box. To secure each strip, apply resorcinol glue to one face of the 1 × 2; position it on the box and nail it firmly into place with 6-penny brass or stainless steel nails set every 4 inches.

If you plan to use the window box for plants that demand a lot of water, make weep holes in the bottom of the box to prevent water logging. Drill a series of 1/2-inch holes every 4 inches along the center of the bottom board. To further aid in drainage, cover the bottom of the window box with gravel before filling it with soil.

Use shelf brackets to attach the windowbox, and add weep holes for plant drainage.
Mount the window box on heavy-duty shelf
brackets secured to the house wall. Weep holes
provide good drainage.

Use heavy-duty shelf brackets to hang the window box. Position the brackets to rest against wall studs under the window -- straight down from the window edges and usually at the center of the window. For wide windows, studs may be found at 16- or 24-inch intervals between the framing studs. Use two brackets for a short window box and three or more for a box 4 feet or longer.

Turn the completed window box upside down and attach the mounting brackets to the bottom with #8 × 1 1/4-inch brass or stainless steel screws; the vertical bracket legs should lie flush with the back of the box. Prop the box in place and secure the vertical bracket legs to the studs of the house wall with #8 × 2-inch brass or stainless steel flathead screws. To fasten the box to a brick or concrete-block wall, use 2-inch lag screws driven into lead masonry anchors. Wearing safety goggles, drill holes for the anchors with a power drill and a carbide-tipped masonry bit; insert the anchors and then drive the screws in flush with the wall surface.

Now add plants and enjoy.

For more ideas on window-related projects, see:
  • How to Repair Windows: Get the tips and instructions you need to correct common problems and keep your windows in good working order.
  • How to Clean Windows: Dirty windows are a big detraction, so follow these directions to keep your glass panes shiny and clear.
  • Kitchen Window Treatments: The kitchen is often the center of a home, so windows there need a special look. Choose the perfect treatment for a warm and welcoming atmosphere.