1. Echo the color of the house.
For a more cohesive look, every window box should contain plants that have foliage or flowers that complement the house or surrounding garden. It's the same principle you use when matching flowers to a pot, framing a painting, or even choosing a shirt and tie.
2. Choose the best plants.
Try mixing plants that cascade from the sides with mounding ones that give heft to the center. Don't plant something that grows too tall and hides the window—unless privacy is your objective. Combine plants that require similar light, moisture, and temperatures. "Don't fight nature," warns Tracee.
3. Pick the right window box.
A hayrack (planted out at left) consists of a metal frame with a coco-fiber liner. It's easy to put up and take down and can cost less than $50. However, you have to replace the liner and soil annually. For about the same money, you can buy a traditional-looking window box made of a composite material that won't rot or warp.
4. Give them consistent care.
Window boxes, like most container gardens, need regular attention. Start with quality potting soil that contains lots of organic matter, stays moist, and drains well. Remove spent flowers promptly to encourage more flowers. Fertilize twice a month using a liquid blossom-boosting product.