Growing no taller than 12 inches, Nemesia a good choice for window boxes. This easy-to-grow flower produces a large, almost flat head, with individual flowers that point in different directions. Nemesia comes in a variety of colors, including shades of yellow, orange and pink, as well as some mixed colors.
Known as Catharanthus, vinca or Madagascar periwinkle, these popular annuals are a good choice for window boxes or flowerbeds. With dark green glossy leaves, periwinkle produces single petal blossoms in shades of pink/rose, mauve or white; some varieties have an alternate colored "eye." Periwinkles grow slowly from seed, which is one reason many gardeners choose to buy them as bedding plants.
Marigolds are a popular flower for gardens and window boxes. Also known as calendula or English marigold, these fast-growing hardy annuals produce bushy foliage and blossoms in shades of yellow, oranges and red; some varieties are variegated. Marigolds re-seed themselves or you can harvest the seeds from spent blossoms to store for the next season.
Petunias are a popular annual for hanging baskets and window boxes, especially the milliflora petunias, which produce 1-inch wide blossoms. Petunias come in a wide range of colors, including pinks, purples, white, reds and some bicolors. Although they thrive in a sunny, south-facing aspect, petunias need protection from strong winds, which damage the flowers.
Also known as Antirrhinum, the common name for snapdragons refers to the ability of the blossom to "snap" when the sides are squeezed. Snapdragons come in various heights. The intermediate -- which grows 18 inches tall -- or dwarf varieties -- which grows 12 inches tall -- work best for a window box. Snapdragons come in a variety of vibrant shades, including pink, orange, yellow, white, purple and some bicolors.
For a mass of color trailing over the edge of the window box, plant lobelia. Producing low-lying foliage, lobelia has small, single-petal blossoms in blue, white, pink, mauve and some two-tones. Some trailing varieties include ‘Cascade Mixed,’ ‘Fountains Mixed,’ ‘Regatta Mixes’ and ‘String of Pearls Mixed.’