Build a Full-length Treated-lumber Window Box Planter to Add a Little Window Dressing to an Eye-catching Window

Build a window box planter gauged to compliment your home and the window sill dimensions. Container gardening of any size and shape lends a little eye-candy to a house and a little green to the environment. Coats of paint can color-coordinate it with the house, while an interior layer of roofing compound will extend the life of the pressure-treated lumber.

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painting the window box green
Step 1

Paint Treated-lumber Planks for the Window Box

Save time by pre-painting the planks for the window box: a two-by-eight, 2 one-by-sixes, and a shorter one-by-six to cut for the ends. The wood is all treated lumber, but is being dressed to coordinate with the existing house trim.

sawing end pieces for the window box planter
Step 2

Measure and Cut End Pieces for the Window Box

Measure and mark the shortest plank for two rectangular end pieces for the window box. Their length will match the width of the large bottom plank. Cut with any saw that makes a straight cut, such as a Japanese handsaw.

drilling pilot holes in the window box
Step 3

Pre-drill Pilot Holes and Secure Ends to Window Box Bottom

Drill three countersunk pilot holes at the lower edge of both end pieces for the window box. Pre-drilling prevents the wood from splitting. Secure both ends to the bottom of the container with rust-proof screws.

adding a bead of construction adhesive to the window box
Step 4

Add Construction Adhesive to the Window Box Edges

Confirm the front and back fit and pre-drill countersunk pilot holes on their bottom edges. Add a bead of construction adhesive and then position the components individually on the window box planter assembly.

securing the window box back with screws
Step 5

Secure the Window Box's Front and Back with Rust-proof Screws

Drive 2.5 inch rust-proof screws into the pilot holes to secure the front and sides of the window box to the bottom. Fill around the screw heads with exterior-grade spackling compound and a putty knife. Let it dry overnight.

applying roofing compound to the window box planter
Step 6

Waterproof the Interior of the Window Box with Roofing Compound

Sand lightly to smooth the window box. Drill drainage holes in the window box bottom. Apply roofing compound to the interior with a putty knife, and then cover the holes with landscape fabric to prevent soil from washing out.

drilling holes to support window box angle brackets
Step 7

Drill Holes for Angle Brackets to Support the Window Box

Mark bracket locations under the sill to evenly support window box weight. Use a bar level to ensure that the holes are level. Drill holes in the masonry with a .5 inch carbide-tipped bit on an electric hammer drill.

hammering lag shields for the window box brackets
Step 8

Mount the Window Box Brackets with Lag Screws

Hammer lag shields/lead anchors into the holes for the window box brackets. They should be flush with the wall. Mount the L-brackets with 2-inch lag screws, tightening them snugly with a socket wrench.

fastening the window box to the brackets
Step 9

Position and Secure the Window Box with Additional Lag Screws

Center the window box planter on the mounting brackets under the sill. Secure the box to the brackets with additional lag screws underneath the planter. Tighten the lag screws with a socket wrench.

layering soil in the window box planter
Step 10

Fill the Window Box Planter with Potting Soil and Plants

Add potting soil to the window box in a generous layer. Position plants and fill in around them with more soil to cover the roots and anchor them in the planter. Finish your container garden by watering the plants.

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