Window boxes are an easy way to add color and curb appeal to a home. For most do-it-yourselfers buying a window box is a little too easy. True bragging rights come from building things rather than buying them.
The length of a window box is a matter of personal choice but measuring the box to be the same length as the window adds a nice affect. Bear in mind, when using a plastic planter inside the window box rather than planting directly, the box will need to conform to the dimensions of the plastic planter. Buy the plastic planter before measuring and cutting boards. The advantages of using a plastic planter are the added durability and easy removal for winter.
Cedar is a good choice of building material as it is durable and not extremely heavy. Cedar is also resistant to moisture, temperature fluctuations and insect damage, according to the Western Real Cedar Lumber Association). The weight of the lumber used will make a difference. It is important that the window box be easy to attach in spring and remove in winter. Lumber measuring 1x8 inches is the perfect size.
The amount of lumber needed depends on the size of the window. Measure the window and draw up plans before heading off to the hardware store. A good set of plans will save on return trips. The list should include your 1x8s, enough to create two long boards of equal size for the sides; two shorter boards of equal size for the ends; a board for the bottom that is 1.5 inches longer and wider than the other boards; and 1.5-inch long galvanized screws.
Place boards together to form the box. Drill pilot holes to prevent wood from splitting. Glue pieces in place with wood glue and secure with screws. Do not forget to drill a few small drain holes in the bottom of the planter. Good drainage will help prevent mold and root rot.
Sand the box and treat the wood with weatherproofing stain or paint with heavy duty outdoor paint. If painting, use a good primer first. Use only paint and primer that is specifically made for outdoor use. Wood stain that is made for outdoor use such as deck stains are perfect for window boxes. One way to add extra protection is with a thin layer of polyurethane.