I have been struggling for years now with my window boxes. I wish I could find an answer for them.
We added window boxes to the front of our house quite a few years ago now. With white shutters and trim and a brown shingled house, window boxes seemed to be just the right touch to add a little color and interest to our otherwise neutral exterior (other than the front door, which I seem to change every few years. Its been red, yellow, blue, and now, green.) But nothing we plant in those boxes seems to be the right formula.
I think the problem is that the lower boxes get more sun and the upper boxes get more shade. One of the upstairs boxes is completely in shadow as its under a rather large Japanese maple tree. So what do you plant that tolerates both shade and full sun well? We've tried geraniums, impatiens, coleus, ivy - all sorts of different things, none of which look great in all the boxes. This year my lower boxes are thriving and full and look beautiful and lush but the ones upstairs are scraggly and limp and simply look horrible.
Now I imagine that they all have different needs in terms of watering and assume perhaps the ones upstairs need either more or less than they are getting. But since I have to water them from the bedrooms (through the screens in the windows) I can't stick my fingers into the soil and see if its too wet or too dry. So I go with an every-other-day schedule. But it doesn't seem to be working.
I wish I were a more educated person when it comes to flowers. I long for beautiful, full, colorful window boxes to make my house look lovely all summer long. My mother had a wonderful green thumb and if she was still around I might have some help in this area. But I'm on my own. And not doing too well.