Here's plans and video to make a window box for your flowers. Easy to build in a weekend. Many window boxes fall apart because they are made of wood, I solved that. And here is Eric's solution: the GardenFork Window Box Plans. Watch the show and then check out our video on window box planting. Below is a window box plan and photos to accompany the window flower box video.
How to make a window flower box
The wood box is made out of pine. It's sized to be just slightly larger than the plastic pot that holds the plants. You can use common pine, be sure to prime it first with a stain blocking primer, else the knots in the wood will bleed through the paint. You can buy a can of stain blocking primer in a spray can, hit all the knots with a second coat, it dries pretty fast.
Give the window box planter several coats of paint, it will last longer that way.
I had to offset the hanger brackets because the side of the house has board and batten style wood siding. If you are attaching this do a house with vinyl siding or clapboard, you might want to slip behind the brackets some shims so the bracket screws don't crush the siding.
When cutting the front and back wood pieces, be sure to cut them 1-½" longer than the width of the inner planter. If you have coated screws, or deck screws, use those, as they are less likely to rust and bleed out of the paint.
This is how I make a window flower box, please tell us about your window box experience below.