Best plants for window boxes by season

Window boxes are shallow, exposed containers -- typically 6–10 inches deep and 24–36 inches wide -- mounted on a structure. They dry out faster than most other containers because their shallow profile limits water-holding capacity, and because they are often elevated where air circulation is.

Window boxes are shallow, exposed containers — typically 6–10 inches deep and 24–36 inches wide — mounted on a structure. They dry out faster than most other containers because their shallow profile limits water-holding capacity, and because they are often elevated where air circulation is higher. Every plant on this list was selected against those constraints.

Per Penn State Extension, window boxes should be watered until water drains freely from drainage holes. In hot weather, twice-daily watering is not unusual. Boxes without drainage holes create anaerobic conditions that kill roots within days.

Box depth and root requirements

Per NC State Extension, most flowering annuals need 6–8 inches of root depth. Perennials and small shrubs used as thrillers need 8–12 inches. If your box is only 6 inches deep, restrict your palette to annuals, compact herbs, and succulents.

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