I used to be a gardener at The Inns of Montchanin in Northern Delaware. I made and installed these flower boxes at my previous home and at one of my rental units. I'm making these in my basement this winter for installation this spring. They come in three basic sizes that fit most windows:

Small: for a bathroom size windows = $100

Medium: for an average windows = $200

Large: (eight feet wide) for a double or bay window = $300

 

I paint my flower boxes with a high gloss, bright white, enamel so the rain washes them clean. They are just as heavy as you think they would be. The largest flower box is a couple hundred pounds wet. You really have to know what your doing to get them to not only stay on a vertical surface, but stay there with the massive weight fluctuation that comes with going from real dry to real wet. I fertilize them with a compost tea I make myself. There is no plant that I know of that can't be grown in a flower or window box. In fact, the more unusual, the better they look. They take a lot of care to get them to bloom like this but standing outside in the sunshine every morning, pruning my plants with one hand and drinking coffee with my other is one of my favorite ways to spend time.