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Q: I'd like to install window boxes below my windows, but I don't know how to go about it. The house has brick-veneer siding and the windowsills are concrete.

— Dolores Chester, Evergreen Park, IL

A: Tom Silva replies: Sounds like a great idea, but leave the windowsills alone. Any holes you drilled there would eventually become an entry point for water.

The most straightforward way to support the box is with sturdy L-shape brackets made out of galvanized or stainless steel. Position them so that one leg of the L is against the wall and hidden behind the planter. This will create a small gap between the wall and the planter, which will prevent moisture from being trapped back there. You can also support the window box with decorative wood or metal knee brackets fastened to the wall below the box. Either way, make sure the brackets are strong enough to bear the weight of a box loaded with plants and soggy soil. For a 3-foot box, I'd probably use three brackets to be safe.

Using a masonry bit, drill a pilot hole into the brick — not the mortar —and fasten the brackets in place using 1½-inch-long masonry screws with the largest-diameter shank that will fit through the bracket holes. (Expansion-type masonry anchors can fracture brick.) Follow the manufacturer's instructions exactly regarding the size and depth of the pilot hole. If the hole is too large, the screw won't hold; too small and you'll never drive the screw in. I always drill the pilot holes about ¼ to ½ inch deeper than the length of the screws and make sure to blow out any dust before driving the screws home.

For the window boxes themselves, choose a durable, rot-resistant species like redwood, cypress, or cedar, and drill holes in the bottom so water can drain. And when you fasten the box to its brackets, use short galvanized or stainless screws — ones that don't go all the way through the bottom of the box.
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