Cactus dahlias are a double-flowering dahlia variety known for their brilliant color variations. These plants feature tubular petals arranged in multiple rows, leading to very full flowers. Unlike other types of dahlias, cactus dahlias do not have a central bud or disk to disrupt their petal arrangement, resulting in a rounded, pom-pom like appearance. They bloom frequently throughout the summer months, making them well-suited to gardeners who like to clip fresh flowers for inside the home.
Though they are native to the western hemisphere, cactus dahlias can be grown in almost any United States climate zone. They are popular with homeowners due to their ability to produce flowers for many months, as well as for their versatile, bright coloring. Cactus dahlias require plenty of room in which to grow, and thrive in sandy, loamy soil. While they can tolerate some shade, they require at least six hours of sunlight each day to survive.
Dahlias can be classified as either single or double flowering varieties based on the characteristics of their flowers. Single dahlias feature a central bud within the flower, and have only one row of petals. These plants tend to be smaller on average than double flowering species. Like other double flowering dahlias, the cactus dahlia features multiple layers of petals with no central disk. These plants grow at least 3 to 6 feet (0.91 to 1.82 m) tall on average, and produce larger, fuller blooms.
The flowers on cactus dahlias generally grow to between 2 and 8 inches (5.1 to 20.3 cm) in diameter, making them larger than many other types of flowers. They range in color from pure white to shades of cream, and many feature deep, vibrant shades like red, purple, orange, or yellow. Some colorful dahlias even feature petals with white tips, which create a uniquely speckled appearance.
Cactus dahlias can be identified by their petals, which are rounded along the entire length. These petals also curve back towards their base for at least half of their length. Semi-cactus dahlias, on the other hand, have much broader petals with a less pronounced curve. These plants come in giant varieties, which have flowers exceeding 10 inches (25.4 cm) in diameter, and large species, where flowers exceed 8 inches (20.3 cm). Medium cactus dahlias feature 6 to 8 inch (15.2 to 20.3 cm) diameter flowers, while floral and miniature version tend to be much smaller, and generally don't grow to more than 4 inches (10.2 cm) in diameter.