How To Make A Window Box

Window boxes are traditional ways of both ornamenting the exterior of a home and improving the view from the inside. They’re a place to put plants where the family will enjoy them the most. The design shown here uses cedar, a wood that doesn’t have to be painted or otherwise treated for long life. And the simple mounting bracket, cut from a single board, allows easy removal of the box to work on the plants or to store it in the off-season.

The best plants for window boxes have a long blooming season and aren’t finicky about moisture or sunlight. Geraniums are an obvious choice because of their plentiful blossoms and ease of care, but you also can grow herbs and attractive vegetables such as hot peppers. The box shown here includes a blue-flowering rosemary, lavender, verbena, pansies, Alpine asters, and a small fern.


  • Tape measure
  • Sawhorses or other flat work surface
  • C-clamps
  • Try square
  • Circular saw or handsaw
  • Dust mask and eye protection
  • Electric drill and twist bits
  • Phillips-head and flat-head screwdrivers

  • 1 x 6 cedar or other lumber
  • 1-1/2″ stainless-steel or brass flat-head screws
  • 2-1/2″ stainless-steel or brass flat-head screws
  • 4-mil plastic sheeting
  • Gravel or pot shards

  • Determine whether the window gets sufficient sunlight for the plants you plan to grow.
  • Make sure the windowsill is sound enough to anchor a box filled with heavy, moist soil. If in doubt, ask a carpenter to check the sill and suggest alternatives for mounting the box.
  • Base the length of the box on the width of the window, keeping them roughly equal.

What you need to know

How To Make A Window Box

  • Level of difficulty: Easy to Moderate
  • Time requirement: 1/2 day
  • Cost estimate: $20 to $40 for a 3′ wide box, depending on the wood you use

Choosing Materials
Outdoor Woods
All wood grows outdoors, of course, but some holds up to weathering better than others. Several species distinguish themselves, even without paint, stain, or varnish. These species include: Western red cedar, Spanish cedar, cypress, and white oak. Although these woods will hold up well without a topcoat, they’ll last even longer if you protect them with either a high-quality outdoor spar varnish or a waterproofing agent.

Step 1 – Lay out parts
The box shown here is made of 1 x 6 cedar, planed on only one side.
The front, back, bottom, and mounting bracket are all the same size–the desired length of the box by the full width of the 1 x 6s. The two sides are 8 1/4-in. long so they’ll cover the ends of the mounting bracket and project slightly at the front of the box.
Lay the parts out on the stock with a try square, using the clearest wood for the front and sides.

Step 2 – Cut parts
Cut the parts to length with a circular saw or a handsaw.
Cut the mounting bracket stock more or less in half with a 45° angle cut. For help in making a straight cut, use the saw’s guide extension, as shown. One half will be attached to the back of the box, and the other to the windowsill.

Step 3 – Assemble box
The box is assembled with brass or stainless-steel screws, driven into pilot holes.

Use 1 1/2-in. screws to attach one-half of the mounting bracket (either half) to the back of the box; place it flush with the top of the back so its bevel is facing down (inset). This creates a pocket for the other half attached to the windowsill.
Attach the sides and bottom to the back, then to each other, with 2 1/2-in. screws.
Again using 2 1/2-in. screws, attach the front to the sides and bottom.
Drill three 1/2-in.-dia. drainage holes in the bottom.

Step 4 – Line box
To protect the wood from moist soil and prevent water stains on the outside of the box, line it with 4-mil plastic sheeting. Cut a piece to cover the bottom and go up the sides and ends.
Poke a hole through the plastic over each drainage hole.
To promote good drainage, spread a layer of gravel or clay pot shards over the plastic-lined bottom of the box.

Step 5 – Install box

Hold the box at the desired height, and mark where the other half of the mounting bracket will attach to the sill.
With the bracket in place, drill pilot holes through it and into the sill; then secure it with five 2 1/2-in. screws.
Set the box on the bracket and add soil and plants. If you live in a climate where the box won’t offer much of a display in the winter, use it as an off-season bird feeder, scattering birdseed over the soil surface.

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