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.
—- title: "Best plants for window boxes by season" slug: best-plants-for-window-boxes hub: plants category: "Plant list" description: "Best plants for window boxes by season: spring, summer, and fall combinations with proven container performance, correct spacing, and watering guidance." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 10 —-
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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Spring window box plants
1. Tulipa spp. (Tulip — spring)
Zones 3–8 | Full sun to part shade | Height: 12–18 inches
Per Cornell Cooperative Extension, tulip bulbs planted in fall at 6-inch depth will bloom reliably in spring window boxes. Chill requirement: 12–16 weeks below 40°F. In warm climates (zone 8+), pre-chilled bulbs are required. After bloom, remove bulbs (they will not re-bloom reliably in shallow containers) and replace with summer annuals.
2. Viola × wittrockiana (Pansy)
Zones 4–8 cool-season | Full sun to part shade | Height: 6–9 inches
Per Clemson HGIC, pansies are the most cold-tolerant spring flowering annual widely available, surviving temperatures as low as 20°F once hardened. They decline when temperatures exceed 75°F consistently. Plant in early spring (4–6 weeks before last frost) and replace with summer annuals as heat builds.
3. Myosotis sylvatica (Forget-me-not)
Zones 3–8 cool-season biennial | Part shade to full sun | Height: 6–12 inches
Per Missouri Botanical Garden, forget-me-nots are a traditional spring filler with sky-blue flowers from March–June. They self-seed prolifically and can be direct-sown in fall for spring blooms. Pull after bloom to prevent unwanted spreading.
4. Narcissus spp. (Daffodil — spring)
Zones 3–8 | Full sun | Height: 8–18 inches (dwarf varieties for boxes)
I plant daffodil bulbs at my Long Island garden every October and have trialed several dwarf varieties ('Tête-à-Tête', 'Jetfire') in window boxes. Per Cornell Cooperative Extension, dwarf daffodils require the same 12–16 week cold period as full-sized varieties but fit window box depths better. Unlike tulips, daffodils are deer-resistant and mildly toxic to most pests.
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Summer window box plants
5. Impatiens walleriana (Common Impatiens — shade boxes)
Annual | Part shade to full shade | Height: 6–18 inches
Per NC State Extension, common impatiens remain the most reliable shade-tolerant flowering annual for window boxes on north-facing or shaded windows. However, impatiens downy mildew (Plasmopara obducens) has devastated plantings across the eastern US since 2012. Per NC State, if you are in an area with documented downy mildew pressure, use Impatiens hawkeri (New Guinea impatiens) or double impatiens, both of which have resistance.
6. Lobularia maritima (Sweet Alyssum — spiller)
Annual | Full sun to part shade | Height: 3–6 inches (trailing)
Per UF IFAS Extension, sweet alyssum is a self-cleaning spiller that blooms continuously in cool weather and recovers from summer heat with light shearing. Fragrant. Attracts beneficial insects. Roots are very shallow (3–4 inches), making it compatible with the shallowest window boxes.
7. Bacopa monnieri (Sutera — spiller)
Annual | Full sun to part shade | Height: 2–4 inches (trailing)
Per NC State Extension, bacopa is a reliable cascading filler-spiller for summer boxes. It prefers consistent moisture (drying out causes tip dieback) but recovers well if cut back. Tiny white or pink flowers cover the trailing stems.
8. Lobelia erinus (Edging Lobelia — spiller)
Annual | Full sun to part shade | Height: 4–6 inches (trailing)
Per NC State Extension, trailing lobelia produces intense blue, violet, or white flowers and cascades 6–12 inches over box edges. It declines in peak summer heat above 85°F but recovers when temperatures drop. Shear back by one-third in midsummer to rejuvenate.
9. Verbena ×hybrida (Verbena — thriller/filler)
Annual | Full sun | Height: 8–12 inches
Per Clemson HGIC, hybrid verbenas tolerate heat and drought better than many summer annuals and perform well in window boxes with good drainage. Deadhead to extend bloom. Prone to powdery mildew in humid conditions with poor air circulation — choose mildew-resistant cultivars like 'Lanai' or 'Superbena.'
10. Petunia ×hybrida (Wave or Supertunia types — thriller/spiller)
Annual | Full sun | Height: 6–12 inches (trailing)
Per NC State Extension, trailing petunia hybrids are among the most widely used window box plants for good reason: they bloom continuously with minimal deadheading, tolerate brief drought, and trail attractively. Fertilize with a water-soluble balanced fertilizer every two weeks for best performance.
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Fall window box plants
11. Viola cornuta (Horned Violet — fall)
Zones 6–9 | Full sun to part shade | Height: 6–10 inches
Per Clemson HGIC, cool-season violas and pansies can be planted in early fall (8–10 weeks before hard frost) for a second season of bloom. They survive mild winters in zones 7–9 and restart blooming in early spring. Use them in the same boxes vacated by summer annuals after the first frost threat.
12. Kale — Ornamental (Brassica oleracea — Acephala group)
Annual/biennial | Full sun to part shade | Height: 12–18 inches
Per NC State Extension, ornamental kale (cabbage) intensifies in color as temperatures drop below 50°F, producing the most vivid display from October to December. It tolerates frost to 20°F. Not edible in the sense of being palatable raw, but non-toxic.
13. Chrysanthemum ×grandiflorum (Garden Mum — fall)
Zones 5–9 | Full sun | Height: 12–24 inches
Per Penn State Extension, fall-purchased mums from garden centers are typically not reliably winter-hardy because they have not been in the ground long enough to establish. Use them as seasonal color in window boxes and treat them as annuals unless you transplant them to the ground 6+ weeks before frost.
14. Carex spp. (Ornamental Sedge — cool season)
Zones 5–9 | Part shade to full shade | Height: 8–18 inches
Per Missouri Botanical Garden, ornamental sedges provide fine-textured foliage interest in fall and early winter window boxes. Carex morrowii 'Ice Dance' and C. oshimensis 'Evergold' are evergreen in zones 6–9 and hold up through multiple frosts. They are the best foliage option for shaded fall boxes.
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Planting density
Per Penn State Extension, window boxes look best planted at 3–4 inch spacing for annuals (closer than ground-level beds) because the display period is short and container fertility can support dense planting with regular fertilization. Use a slow-release granular fertilizer at planting, supplemented with liquid fertilizer every two weeks.
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Frequently Asked Questions
How do I prevent window box plants from drying out? Per Penn State Extension, add hydrogel crystals to the potting mix at planting, install a self-watering insert with a reservoir, or water twice daily in hot weather. A 1-inch layer of coarse mulch on the surface of the box reduces evaporation by 30–40%.
Can perennials overwinter in window boxes? Per UMN Extension, perennials in window boxes are exposed to temperature extremes on all sides, not just the top. Treat any perennial in a shallow, mounted box as two hardiness zones colder than your USDA zone. What is hardy to zone 5 in the ground may not survive a zone 6 winter in a window box.
Should I line window boxes with moss or plastic? Per Penn State Extension, coco coir liners and moss liners both allow drainage and airflow but dry out faster than solid plastic boxes. For hot, sun-exposed locations, a solid plastic liner with drainage holes retains moisture longer. In cool, shaded locations, coco liners reduce root rot risk.
What is the minimum box depth for flowering plants? Per NC State Extension, annual flowers need 6–8 inches of growing depth. Below 6 inches, restrict plantings to sedums, succulents, sweet alyssum, and creeping thyme.
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Sources
- Penn State Extension — Container Gardening
- NC State Extension — Plant Profiles
- Clemson HGIC — Pansies
- Clemson HGIC — Verbena
- Cornell Cooperative Extension — Bulbs
- Missouri Botanical Garden — Plant Finder
- UF IFAS Extension — Sweet Alyssum
- UMN Extension — Container Overwintering