A window flower box is a form of container gardening that may be filled with beautiful annuals, perennials, biennials or a blend of all and mounted outside a window. It is a work of art in itself when all the flowers are in bloom, displaying a bold show of color and aroma that is carried indoors on windy days. Most window boxes come with two mounting brackets and accompanying hardware. Even a novice gardener can install a flower box outside a window of his house or apartment and enjoy a burst of color.
Purchase a window flower box that is 5 inches longer than the length of the window. Determine its location below the window where you want to install it, so you can mark the appropriate spots for the brackets. Step back to visualize how the window box will look at different heights before making your final decision.
Use chalk to mark on either side of the window, just below it, the two spots where you will install the brackets. Measure 6 inches below the windowsill if your windows push outward when opened, or an inch below if the windows are double-hung or sliding.
Begin installing the window box on one side of the window by placing the first bracket directly over the chalk mark. Use a countersink drill bit to drill a pilot hole for the top screw. Drill the pilot hole into the sliding itself for vinyl or aluminum sliding.
Use the accompanying screws to attach the bracket to the sliding, through the pilot hole you drilled. Use 2- or 3-inch galvanized decking screws if your flower box did not come with mounting screws, or if you built it yourself. Use a carpenter's level to make sure the bracket is level as you install the other two screws into the mounting bracket.
Move to the other side of the window and hold the second bracket over the chalk mark. Check to make sure it is level with the previous bracket, using a carpenter's level. Make necessary adjustments by relocating it a bit so they are both in line with one another, and repeat the process to attach it firmly.
Carefully lift and place the window flower box on both the brackets. Step back to visually determine how much overhangs on either side, and position it so it is equal on both sides.
Drill two holes through the back of the flower box and directly over the top edge of the brackets. Insert 2-inch decking screws into the holes to attach the flower box to the brackets securely. Fill your flower box with potting soil and plants.