I got the idea from here:
http://www.birdsandblooms.com/...
There is a pretty lengthy thread on DG about this project in Trash to Treasure. After much discussion on how-to's, I just jumped in and did it my own way, which I do NOT recommend, LOL! I backed the shutter with burlap stapled all around, filled with soil, then stuffed sphagnum moss in all of the slats, then planted. If I were to do it over, I would flip the shutter upside down, put a layer of sphagnum moss down first, then the soil, then staple the burlap to the back. Or, one poster suggested making a shutter/moss/soil sandwich... shutter facing down, then moss, then soil, then more moss, then another shutter. That way, you could plant both sides.
Here is a window box I planted up the other day... periwinkle paint is getting lots of use this year! Luckily, the fuchsias didn't freeze last night... we did have a frost but apparently my shade garden has it's own microclimate and it's protected from the wind.