1. Paint the window box and decorative brackets to match the window frame.
2. Mount brackets to the wall beneath the windowsill, then screw the box bottom to the top of the brackets. If your planter is very heavy, find the wall studs when mounting or use hollow-wall anchors.
3. Mix foliage and blooming plants in your window box. You may want to leave them in pots for ease and cleanliness. Be sure to use plastic saucers beneath the pots to catch water drips.