The first step in building your DIY window box is to measure the length of the exterior area where the planter is to be installed. This finished product will measure 10 ft. in length, so you’ll want to have a helper when measuring the space for your DIY window box and building the planter. Choose an area below the window or windows where the plant hangers for the box can be anchored into wood securely. 

Tip: Adjust the length of the wood to fit your window space. 

Use a circular saw to make these cuts of the boards for your planter box.  

• Two 1” x 12” x 12 3/4" cuts from the 1” x 12" x 3' board 
• Two 9’ 9" cuts from the two 2 x 2" x 10' boards  
• Four 9 3/4" cuts from two of the 2 x 2" x 2' boards  
• Two 11" cuts from one of the 2 x 2" x 2' boards 
• One 11 1/2" cut and two 12 3/4″ cuts from the 1” x 2" by 4' board

• Use one 1” x 12” x 10' board as your base.  
• Place one 2 x 2" x 9' 9” board on either side of the base, even with the edge and leaving 1 1/2 in. on each end.  
• Glue the boards to the base with wood glue.  
• Clamp the boards to the base in three different places. While clamped, drill six pilot holes evenly spaced. Allow at least an hour for the wood glue to set. 
• Secure the pieces with six screws through the side boards into the base board. Repeat on the other side. 
• Attach the two 2 x 2” x 11". boards to the short edges of the base to complete the rectangle. Use the wood screws to secure each piece. 

• Attach a 3-inch hole saw to a power drill.  
• Cut six drainage holes into the base. Space the holes as evenly as possible but do not drill a hole where a window box bracket will be placed underneath. 

• Take two 2 x 2” x 9 3/4" boards and place them on a 1” x 12” x 12 3/4" piece. Position them 7 3/4″ apart with 3/4 of an inch on either side and flush at the top. Glue and hold with clamps. 
• Once the glue dries, place on the right side of the base. The 2 x 2 boards should be on top of and lined up with the 2 x 2 boards on the base.  
• Use three screws to secure the bottom and two more screws in the sides to secure the pieces together, creating the right wall of the box. Repeat for the left side. 

• Run a 1” x 12” x 10' piece along the front of the box. Have your helper hold this in place while you insert eight wood screws evenly spaced along the bottom into the base.  
• Use three more screws up each side of the front to secure to the side walls. Repeat the step for the back of the box. 

• Place a 1 x 2“ x 10’ 1/2" piece of trim along the top front. Let it hang over 3/4 in. on each side. Glue and use clamps to hold the trim in place.
• Take two 1 x 2 x 12 ¾ in. pieces of trim and place on the top right and left side. Glue and hold with clamps. 

Your DIY window box is completed, so now is the time to give it a coat of paint. A painted box lasts longer when exposed to the elements. 

Apply wood putty to cover each screw head. Sand down once dry.  

Choose an exterior primer and paint in your favorite color, and paint box. Let the paint dry. 

A window planter filled with soil can be very heavy. Before attaching the plant box mounts under the window of your house, attach wooden pieces called cleats first to secure the box to the exterior wall.   

• Using a circular saw, cut the 2 x 4 in. board into three 8-in. pieces 
• Hold one of the cleats against the exterior wall. Drill two pilot holes for the concrete screws. 
• Drive 3/4-in. concrete screws through each of the pilot holes to secure the cleat to the wall. 
• Repeat the process for the other two cleats. 
• Attach the plant box mounts to the cleats. Make sure the mounts are attached securely to the cleats. 
• Place the window box on the plant box mounts and secure in place with screws. 

You're now ready to prepare your DIY window box for planting.

• Lay landscape fabric along the bottom of the box. 
• Add quality potting mix. 
• Use flowers or edibles suited for your region and for the amount of sun the planter gets.