Flowers planted in window boxes give your home and garden a contained area of dramatic color. Be sure that the window box has drainage holes so the soil does not become waterlogged and cause root rot. Use a lightweight soil mixture in the boxes. Regular soil absorbs water and becomes extremely heavy which risks breaking the box loose from its supports. Flowers benefit from the extra care and ideal soil mixture when grown in a box. Choose young, small plants, since they adapt better than old, large plants. Plant your flowers close together in a window box.
Creeping zinnia (Sanvitalia procumbens) is a 6-inch tall spreading annual that is commonly used as a flowering groundcover. The gray-green, oval leaves are 2 inches long. Yellow and orange ray-like petals surround a dark purple center, creating a blossom that is 3/4 of an inch across. Creeping zinnia blooms from spring through fall. It does best in a window box that receives full sun. Deadhead the fading blossoms to promote the production of more flowers.
Fan flower (Scaveola aemula) grows 8 to 10 inches tall. This thick-stemmed annual flower produces dark green, triangular leaves with serrated edges. Blue, white, pink and purple blossoms appear in the summer. Five petals appear all on one side of the flower head, resembling a fan with a yellow center. Fan flowers thrive in hot, sunny and dry growing conditions. This flower suffers from root rot if the window box does not provide the proper drainage and the soil stays wet.
French marigold (Tagetes erecta) is an annual that creates mounds of green feathery leaves. These leaves are not as stiffly upright as other types of marigolds. This flower grows 6 to 15 inches tall but spreads out twice as wide. Red, orange and yellow flowers are usually marked with dark red, maroon and rust colors. The ruffle-edged marigold blossoms bloom from summer until fall. These hardy flowers enjoy full sun exposure and tolerate frosty weather. French marigolds will attract butterflies and hummingbirds to your flower boxes.
Heliotrope (Heliotropium arborescens) is a bushy annual reaching 18 to 36 inches in height. The dark green leaves have a purplish tint. Blue, violet and white flowers appear in the middle of summer and last until early autumn. The tiny heliotrope blossoms cluster on the ends of the stems. Heliotrope needs shade during hot summer afternoons. This flower produces a vanilla-like scent and attracts butterflies to your window box.
Vinca (Catharanthus roseus) is a hot weather annual flower growing 7 to 24 inches tall. Vinca produces a mass of oval, green leaves with a light green vein down the middle. White, pink, purple and lavender blossoms appear from spring until the first fall frost. The lax stems cascade over the edges of window boxes. Let vinca dry out to the touch between waterings in order to prevent root rot.