If your window box sits in the full heat and sun, you'll need to choose your plants carefully. A box full of flowers that fried in the sun certainly isn't going to add to your home's appeal. For best results, fill your window box with lightweight potting soil, which offers good drainage, allows air to circulate around the root system and retains moisture.
Cheery yellow flowers will blossom in your hot and sunny window box when you plant Tazetta daffodil “Minnow” (Narcissus “Minnow”) and melampodium “Derby” (Melampodium divaricatum “Derby”). In early spring, “Minnow” daffodil puts out fragrant flowers with creamy-white petals surrounding yellow cups. This drought-tolerant bulb returns year after year in U.S. Department of Agriculture plant hardiness zones 5 through 9. “Derby’s” flowers come out from spring to frost. This annual tolerates hot and humid conditions, but the tallest stems may droop in regions with high midsummer temperatures.
Gaze at pretty pink flowers in your sunny window box when you plant select heat-tolerant plants. Ornamental onion (Allium karataviense) produces fragrant, dull pink, butterfly-attracting flowers on short, erect stems from mid- to late spring in USDA zones 4 through 8. This biennial is easy to grow in sandy soil. Mexican fleabane daisy “Blood Sea” (Erigeron karvinskianus “Blood Sea”) blooms with petite daisies that emerge white and mature to rose-pink from late spring into mid-fall in USDA zones 8 through 10. This Mexican native is just the right choice for regions with hot, arid summers.
Flowers in a Range of Colors
Decorate your hot and sunny window box with drought-tolerant perennial flowers that come in a range of colors. Zonal geranium (Pelargonium x hortorum) flowers freely in USDA zones 10 through 11 and its blossoms come in red, pink, purple orange and white. This evergreen grows up to 3 feet tall. Garden verbena (Verbena x hybrida) flowers from mid-spring into fall in USDA zones 9 through 10 and its butterfly-attracting blossoms come in red, white, yellow, red, blue and purple. Deadheading encourages new flowers. Both geranium and verbena can grow as annuals in cooler climates.
A cascading growth habit adds vertical interest. Trailing verbena “Homestead Purple” (Verbena “Homestead Purple”) will send its clusters of purple flowers tumbling over the side of your window box from late spring into midfall in USDA zones 7 through 9. The fragrant, pink flowers on marjoram “Kent Beauty” (Origanum “Kent Beauty”) will dangle over the side of your window box from late spring to early fall in USDA zones 6 through 9. Its leaves don’t offer the pungent flavor of culinary varieties.