I just happen to love window boxes and miss seeing them in the more modern neighborhoods these days. My neighbors who lived across the street from us had just painted their older rather plain, small house a medium gray with white trim. Clean, but boring I thought. With two large windows on each side of the front door, I had visions of painting the front door red and adding 2 red window boxes beneath those windows. Talk about adding some impact!
Window boxes can take a plain nondescript house and give it the look of a charming country cottage in no time. Window boxes are also particularly wonderful when you are limited for planting space in a small yard. You can fill them with low growing and trailing flowers, vines or even herbs. You may be hard put to find ready-made window boxes at your local garden store these days, but they are still available online.
If you want to make your own window boxes, cedar or redwood would be the wood of choice. If you can't find some kind of a plastic or metal liner to fit, I would further protect the wood by lining the boxes with plain old tarpaper before adding the planting mix. You can then mount them to the window frames with the proper sized brackets. Your neighborhood hardware store can guide you in the right direction.
Make sure you drill some holes in he bottom of the window boxes for good drainage and water daily during the summer months. Once every few weeks are so, add some fertilizer for container plants, then sit back and enjoy beautiful blooms from both the outside and inside of the house.
Some good flower choices for window boxes would be geraniums, marigolds, trillium, alyssum, and any other low growing flowers that love the sun. For the shady side of the house, try fuchsias or the beautiful non-stop begonias. Some useful herb choices would include chives, rosemary, parsley and thyme. If you like fresh mint, don't plant any other herb in that particular window box as the mint will take over all other plants.