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How to Hang a Window Box

TOH general contractor Tom Silva shows you how to hang a flower box, and TOH landscape contractor Roger Cook tells you how to fill it and maintain it

Add a splash of color and visual interest to your home with a traditional wooden window box. These charming wood boxes have been used for centuries the world over to dress up plain, somber windows. And now you can install one in just an hour or so with a minimal amount of effort or expense. Here, This Old House general contractor Tom Silva shows the best way to install a prefabricated window box. According to Tom, successful installation depends on proper placement of the box and braces on the house, and securely attaching the components with the appropriate fasteners.

And if your green thumb is a bit out of shape, don't worry. This Old House landscape contractor Roger Cook gives his top tips for preparing, planting and maintaining window boxes. So take the afternoon off, roll up your sleeves and hang a window box or two.

Step 1

Window Box Overview

Illustration by Gregory Nemec
Step 2

Mark the mounting location

Photo by Mary Beth Montgomery

If your home has double-hung or sliding windows, measure down 1 inch from the underside of the windowsill directly below one side of the window frame and make a pencil mark to locate the top of the bracket.

For an out-swinging window, measure down 6 to 8 inches.

Tip: Have the window box and brackets handy, already painted or stained.

Step 3

Install the top screw on the bracket

Photo by Mary Beth Montgomery

Hold the first bracket with its top on the pencil mark.

Mark the bracket for the top screw hole so it falls near the bottom of the first course of siding below the window.

Using a countersink bit on a drill, bore a pilot hole and counterbore into the bracket on the mark.

Fasten the bracket to the house with a 3-inch-long galvanized decking screw through the pilot hole.

Tip: If mounting to vinyl, aluminum, or fiber cement, bore a pilot hole through the siding as well. The screw will bite into the sheathing behind it.

Step 4

Check for plumb and install the second screw

Photo by Mary Beth Montgomery

Hold a 2-foot level against the side of the bracket to ensure that it's perfectly plumb.

Bore a pilot hole and counterbore for the second screw through the bracket just above the horizontal leg, where it will be hidden by the window box.

Drive another 3-inch screw through the bracket.

Step 5

Install the second bracket

Photo by Mary Beth Montgomery

Hold the second bracket in position under the window-sill, lining it up with the window frame.

Lay a 4-foot level across the two brackets; raise or lower the second bracket until the two are level.

Drill a pilot hole and counterbore into the bracket near the bottom of the siding as in Step 2.

Attach the bracket to the house with a 3-inch decking screw, then follow the directions in Step 3 for plumbing the bracket and driving the second screw.

Step 6

Center the window box

Photo by Mary Beth Montgomery

Set the empty window box on top of the two brackets. Be sure that the angled side of the box faces outward.

Center the box by measuring the overhang on the brackets (as shown).

Tip: A filled window box is surprisingly heavy; don't add the soil and plants until after the box is installed.

Step 7

Fasten the box to the brackets

Photo by Mary Beth Montgomery

Drill and counterbore pilot holes into the upper rear edge of the box, directly in front of each bracket.

Drive a 2 1/2-inch-long galvanized decking screw through the box and into the upper end of each bracket.

After hanging the flower box, fill it with container soil or potting soil, then plant away.