Window Box Plants for Full Sun, Part Sun and Shade

Window boxes fail for one reason more than any other: the plants were chosen for how they looked at the garden center, not for how much sun hits that particular window. A south-facing box can bake at well over 100°F on a July afternoon, while a north-facing box under a deep eave may never see direct light at all. Matching window box plants to the exposure of each window is the fastest way to get boxes that stay full from spring to frost.

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For full sun (six or more hours, typical of south and west windows), choose heat lovers such as geraniums, lantana, trailing verbena, calibrachoa, portulaca and ornamental grasses. For part sun (three to six hours, usually east windows), fuchsias, begonias, coleus, torenia and lobelia do well. For shade (under three hours, often north windows), rely on impatiens, caladiums, ferns, heuchera and trailing ivy or creeping jenny.

Each exposure gets its own list of specific plant picks, along with how many plants fit per foot of box and the watering and soil habits that keep a window plant box looking full all season.

Window Box Plants Start With Your Window Exposure

Compass direction is a starting point, but trees, porches, neighboring houses and overhangs all change the real number of sun hours. Spend one sunny day checking the box spot every hour or two and note when it is in direct sun.

• Full sun: 6 or more hours of direct sun, often including hot afternoon light. Common on unshaded south and west walls.
• Part sun or part shade: 3 to 6 hours, ideally gentle morning sun. Common on east walls and partially shaded south walls.
• Shade: under 3 hours of direct sun, or only filtered light. Common on north walls and under deep eaves or porches.

West exposure deserves special mention. Even with only four or five hours of direct sun, afternoon light is intense and boxes heat up. Treat west windows as full sun for plant choice and as extra-thirsty for watering.

Best Window Box Plants for Full Sun

South and west boxes need plants that tolerate heat, wind and soil that dries out fast. Combine an upright “thriller” or two, a mounding “filler” and a trailing “spiller” for a full look.

Upright and mounding

• Zonal and ivy geraniums: classic, heat tolerant and long blooming
• Lantana: handles heat and drought and draws butterflies
• Angelonia: upright spikes that keep blooming through summer heat
• Dwarf zinnias and marigolds: compact, cheerful and easy
• Ornamental grasses or spikes: add height and texture
• Herbs: rosemary, thyme and basil suit a sunny kitchen window

Trailing

• Calibrachoa (million bells): dense trailing color, needs regular feeding
• Trailing verbena: tough and long flowering
• Sweet potato vine: bold foliage; vigorous, so trim as needed
• Portulaca and trailing succulents: excellent for the hottest, driest boxes
• Silver trailing foliage plants: light color softens bright blooms

Pale colored boxes stay cooler than dark ones in full sun. If your box is black metal on a west wall, an insulating liner or a lighter box can prevent cooked roots.

Best Window Box Plants for Part Sun

East-facing boxes get cool morning light and afternoon shade, which is the easiest exposure to plant. Many sun and shade plants overlap here.

• Fuchsia: dangling blooms that prefer cool mornings and shaded afternoons
• Wax and tuberous begonias: steady color with little fuss
• Coleus: huge range of leaf colors; pinch flower spikes to keep it bushy
• Torenia (wishbone flower): mounding to trailing with small tubular flowers
• Lobelia: fine-textured trailing blue or white; can fade in summer heat
• Bacopa: small white or lavender trailing flowers
• Nemesia and violas: excellent cool season choices for spring and fall

Part sun boxes often dry a little slower than full sun boxes, so check before watering rather than watering on a fixed schedule.

Best Picks for Shade

North windows and deeply shaded boxes call for foliage first and flowers second. Strong leaf color and texture give a shade box impact all season.

• Impatiens: the standard for shade color; choose disease resistant types if downy mildew has been a problem in your area
• Caladiums: large patterned leaves in pink, red, white and green
• Ferns: compact types add fine texture and height
• Heuchera (coral bells): foliage in lime, burgundy and silver; perennial in many climates
• Browallia and shade-tolerant begonias: reliable blooms with little sun
• Creeping jenny and trailing ivy: bright or dark green spillers
• Polka dot plant and hostas (small varieties): leaf interest in tight spaces

Shade boxes stay damp longer. Water less often, use a mix that drains freely, and watch for fungus gnats or rot if the soil never dries at the surface.

How Many Plants Per Box: Spacing by Length

Window boxes look best planted more densely than a garden bed, because you want a full display right away and the season is short. A practical rule is roughly 3 plants per foot of box length for small and medium plants, using a mix of upright, mounding and trailing.

Place uprights toward the back (against the house), fillers in the middle, and trailers along the front edge and the ends. Vigorous plants like sweet potato vine or coleus count as two plants, so reduce the total when you use them.

Planting Steps

1. Check drainage. The box needs holes in the bottom. Add a liner if the box is wood or coir, and make sure the liner drains too.
2. Use a quality potting mix. Skip garden soil, which compacts. A mix with some compost holds moisture without staying soggy.
3. Add slow release fertilizer. Mix it in at planting according to the label, then supplement with liquid feed every couple of weeks for heavy bloomers.
4. Arrange before planting. Set the nursery pots in the box to check the layout and spacing.
5. Plant at the same depth. Loosen circling roots, plant at the same soil level as the nursery pot, and fill gaps firmly.
6. Water thoroughly. Soak until water runs from the bottom, then top off any settled spots with mix.

If you work from a ladder to plant or water boxes on upper windows, set it on firm, level ground and keep three points of contact. Better yet, choose boxes that can be planted from inside the window or lifted down from the bracket.

Watering and Ongoing Care

Window boxes hold a small volume of soil, so they dry faster than ground beds. In midsummer, a full sun box may need water every day and sometimes twice on hot, windy afternoons. Shade boxes may go several days. Push a finger an inch into the soil; if it is dry, water until it drains.

A self-watering window box with a reservoir in the base smooths out those swings, which is especially helpful for sunny or hard to reach windows. Fill the reservoir instead of soaking from the top, and empty it during long rainy spells so roots do not sit in standing water.

Deadhead spent flowers on geraniums, zinnias and marigolds. Cut back leggy calibrachoa or petunias by a third in midsummer to restart blooming. Replace tired cool-season plants like pansies and lobelia with heat tolerant fillers once summer arrives.

Troubleshooting

Plants wilting by afternoon even after morning watering: The box is too small or too hot for the plants. Add a reservoir insert, use a larger box, or switch to drought tolerant choices.

Leggy plants with few flowers: Not enough sun. Move the plants to a shade-friendly list or relocate the box.

Yellow lower leaves: Usually overwatering in a shade box, or hunger in a sunny box. Check soil moisture before deciding which.

Water staining the siding below: Water more slowly, use a liner with a drip tray, or choose a self-watering design.

Cost Ranges

Annual plants usually cost a few dollars each in small pots, more in larger sizes. Filling a 36 inch box typically runs somewhere between a modest and a moderate amount depending on plant size and if you choose premium varieties. Boxes themselves range from inexpensive plastic to higher priced cedar, metal or self-watering designs. Seasonal refreshes in spring, summer and fall add up, so perennials like heuchera and ferns can save money over time.

When to Call a Pro

Most planting is easy DIY, but call a handyman or carpenter if boxes need new brackets anchored into framing or masonry, or if the windows are on a second story or higher where work requires an extension ladder or lift. Professional landscapers can also handle seasonal changeovers for multiple boxes.