A well-planted window box follows a simple formula: something upright, something full, something trailing.
The Thriller-Filler-Spiller Formula
A taller "thriller" plant like a small ornamental grass or geranium provides height and focus; mounding "filler" plants like petunias or lobelia fill the middle; trailing "spiller" plants like ivy or bacopa cascade over the edges. This simple combination reliably produces a full, professional-looking box.
Watering More Than You'd Expect
Window boxes dry out much faster than in-ground beds due to their small soil volume and exposure to wind, often needing daily watering in hot weather. A box that feels light when tapped or lifted slightly is usually a sign it needs water.
Feed Regularly for Continuous Bloom
Frequent watering washes nutrients out of a window box's limited soil quickly, so a light feeding every couple of weeks during the growing season keeps plants blooming steadily rather than fading by midsummer.
