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Wedel's Nursery, Florist and Garden Center

Build an Indoor Window Planter

Level of difficulty: Beginner

An indoor window planter livens up your counter or table in front of a window, or hanging on decorative brackets that you install just below the window. The container is waterproofed on the inside and will not be exposed to harsh weather conditions, so you can choose a wood and finish to complement or match your interior woodwork. You can even try your hand at a decorative painting technique such as sponging or stenciling. If you plan to paint the planter, build it with any select (knot-free) grade of wood such as pine or poplar. If you prefer a natural finish, consider a fine hardwood such as oak or maple. Normally a planter might have a vertical back but we angled both faces, enabling you to turn the planter 180 degrees so the plants won’t all lean toward the sun.

Tip :  The waterproofed interior of the planter means you can put soil directly into it, but not all plants have the same water needs. Setting pots in the planter and filling the gaps with pine bark or a similar mulch will also make it easier to change plantings and maintain the planter.

Materials List

    Tape measure


    1″x8″ knot-free lumber (ends, faces, and opt. shelf)

    Drill and 3/32″ twist bit

    1″x6″ No. 2 pine (bottom)

    Waterproof wood glue


    Hammer, nail set, and 6d galvanized finishing nails, or: 2″ finishing screws and #1 Phillips screwdriver or bit

    Circular or table saw (opt.)

    Pair of 6″ decorative shelf brackets with screws


    Plasti-Dip spray or 1/2-pt. can (found at most hardware stores and home centers)

    Rubber sanding block or finishing sander

    Paint or other finish and related supplies

    Sandpaper (80-, 120-, and 220-grit)

    Plants, pots, mulch, gravel, landscape fabric, and other planting supplies change plantings and maintain the planter.


1. Determine the Dimensions
Your indoor window planter will probably look best if it is as wide as the outside dimension of the window casing and no wider than the window stool (interior windowsill). The planter should be at least deep enough and high enough to accommodate a 6-in.-diameter flower pot. The size of the design shown (see below), which uses 1×8 lumber for the ends and faces and 1×6 lumber for the bottom, is a suggested minimum.
Windowbox Dimensions
2. Cut and Mill the Parts
Cut the front, back, and ends from your “good” lumber. You can use a lesser-grade lumber, such as No. 2 pine, for the bottom.

2a. Bottom: If you have a circular saw or table saw, set the bevel adjustment to 5 degrees, and rip (cut with the grain) both edges of the bottom to 5 inches wide (at the widest point). Alternatively, use a plane to bevel a 5-degree angle on the two edges. Cut the bottom 3/4 inch shorter than the length of the faces so it will be recessed 3/8 inch when assembled.

2b. Ends: Rip the 1×8 to 6 inches wide (which corresponds to the height of the ends), then cut the sides at an 85-degree angle to create a 5-in. and a 7-in. base on these two trapezoidal pieces.

2c. Faces: Rip or plane a 5-degree bevel along the bottom edge of each piece.

3. Sand Parts Smooth
Use a rubber sanding block or finishing sander and sand all the pieces smooth, starting with 80-grit, then 120-grit, and finishing with 220-grit sandpaper. Sand along the length of the boards (with the grain).

4. Assemble the Planter
Brush glue on all edges of the bottom and rest it on 1/2-in.-thick spacers. Clamp the two ends onto the bottom and predrill 3/32-in. pilot holes for the fasteners. Secure the ends to the bottom with 6d galvanized nails or with finishing screws. Glue the front and back edges of the end pieces; similarly clamp and attach the faces to the bottom and the ends. Wipe off excess glue with a damp cloth and touch up with your sander as needed.

Tip :  Pre-drilling prevents the fasteners from splitting the wood (especially hardwoods) and makes it a lot easier to accurately drive the nails or finishing screws.

5. Waterproof the Interior
Mask the top edge of the planter and apply Plasti-Dip to the interior surfaces. Plasti-Dip, available in spray cans or as a brush-on liquid, forms a flexible, waterproof membrane when it dries. It is available in yellow, black, red, blue, and clear.

6. Apply a Finish
When the interior dries, reposition the masking tape over the top inside edge and finish the sides and top with any interior paint, stain, or polyurethane finish.

7. Install the Planter under a Window
To mount the planter on shelf brackets or on a shelf supported by brackets, you must install those brackets with screws into solid wall framing. If you mount the planter to the brackets, glue 1/2-in. wood spacers to the bottom at the bracket locations. Locate studs with an electronic stud finder or by a combination of tapping (listening for hollow and solid sounds) and observing the location of any baseboard nails.

Tip :  If brackets secured to studs would not be symmetrically located, screw a board to the wall and then secure the bracket to the board.

8. Setting Your Plants and Flowers
If you plan to place soil directly into your planter, you must provide drainage. Put at least 1-1/2 inches of crushed stone in the bottom of the planter and cover it with a layer of landscape fabric before you add soil and plants. If you prefer to keep plants in their pots, simply put the pots in the planter and fill around them with sphagnum moss, pine bark, or similar mulch.

Tip :  Set smaller pots on blocks of wood or on some mulch so their tops will be even with those of larger pots.

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