How-to Guide
Window Box Planting and Care
The short answer
Use a box with drainage holes and fill it with a lightweight soilless potting mix — not garden soil, and skip the myth of pebbles in the bottom, which don't improve drainage. Window boxes dry out fast, so expect to water daily or even twice daily in summer heat, checking the mix an inch below the surface and feeding every two weeks with half-strength liquid fertilizer.
Match plants to the window's exposure: sun-lovers like petunias, geraniums, verbena, and sweet alyssum for bright windows; impatiens, begonias, fuchsia, and pansies for shady ones. Plant more densely than you would in a bed, with upright plants toward the center and back and trailing plants at the edges to spill over the front.
The box: size, drainage, and soil
For looks, size the box to run the full width of the window. For plant health, the non-negotiable is drainage: the box must have drainage holes so the mix never stays waterlogged. Don't bother layering gravel or pebbles in the bottom — it doesn't improve drainage, it just steals root space.
Fill with a lightweight, soilless potting mix rather than garden soil. Soilless mixes give the drainage, aeration, and water-holding that a shallow box needs; garden soil compacts, drains poorly, and can drag pests and weed seeds up to the window.
Watering and feeding — the part people underestimate
A window box holds little soil, sits in the sun and wind, and dries out far faster than a garden bed. In summer, plan on watering daily, and in real heat sometimes twice a day. The reliable test is to feel the mix about an inch below the surface and water whenever it's dry there rather than watering on a fixed schedule.
All that watering flushes nutrients out of the small soil volume, so feeding is part of the routine, not optional. Extension guidance is to feed every two weeks from spring through summer with a complete liquid fertilizer diluted to half strength. Deadhead spent flowers to keep annuals blooming.
The watering reality is the same one that trips people up with hanging baskets — see our hanging basket care guide for the same fast-drying, feed-often approach.
Choosing plants by exposure and arrangement
Match plants to the window's light. Sunny windows (especially south-facing) suit petunias, marigolds, geraniums, verbena, and sweet alyssum. Shady windows (north-facing, or shaded by the house) do better with impatiens, pansies, begonias, caladiums, and fuchsia; keep the shade plantings, impatiens especially, constantly moist.
Arrange for the classic layered look: plant more closely than you would in a flowerbed, put upright plants toward the center and back for height, and set trailing plants along the front edge to cascade over the box. Mixing colors, shapes, and textures within that structure is what makes a small box read as full and intentional.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Clemson Cooperative Extension HGIC — Hanging Baskets & Window Boxes — Window boxes should extend the entire width of the window and must have drainage holes, and putting pebbles in the bottom does not improve drainage; use a lightweight soilless potting mix; containers can dry out very quickly so daily or even twice-daily watering may be necessary, checking the mix one inch below the surface; feed every two weeks from spring through summer with a complete liquid fertilizer diluted to half strength; plant much closer than in a flowerbed with trailing plants at the edges and upright plants at the center/back; sun plants include petunias, marigolds, geraniums, verbena, and sweet alyssum, while shade plants include impatiens, pansies, begonias, caladiums, and fuchsias.