Giant allium is a common name for a flowering perennial plant that grows from a bulb and produces giant ball-shaped clusters of purple blossoms. The scientific name for the plant is Allium giganteum, and it belongs to the same family as edible onions. Some other common names include flowering onion and ornamental onion. The flowers are very attractive and showy; they can attract desirable wildlife. The giant allium has several uses in the garden and is relatively easy to grow and care for.
The giant allium grows from a large bulb that resembles an onion and measures 2 to 3 inches (5 to 7.6 cm) across. Near the ground, the bulb produces a radial arrangement of narrow, long, strap-like, green leaves. The leaves are often at least 18 inches (45 cm) long. As its name suggests, a mature giant allium typically grows to a generous size of between 4 and 6.5 feet (1.2 to 2 m), although most of this height is the from the flower stalk.
Flowers of the giant allium bloom in densely packed ball shaped clusters. Each bulb produces a single thick, leafless stalk that supports one flower ball. Individual flowers are tiny, star shaped blossoms, with a color that ranges from soft lavender to a darker, more vivid shade of purple. The cluster of flowers is usually the size of a softball, about 6 inches (15 cm) in diameter. There is also a variety called the Globemaster Allium which produces flower clusters that are approximately the size of a soccer ball.
Some closely related species to the giant allium include onions, garlic, and leeks, as suggested by a few of the plant's common names. The whole plant smells like onion, particularly the leaves. The scent is intensified it the leaves are bruised or crushed and is supposed to repel moths. Although it's not commonly eaten, the leaves and bulb are reputed to be edible with a mild onion taste.
The huge blossoms of the giant allium are very showy, and can last for several weeks. They are attractive to butterflies, bees, and many types of birds, and are often used in flower beds and borders in the garden, as well as being a popular cut flower. They should be watered regularly during the growing season and can benefit from a protective layer of mulch in the winter. The bulbs should be planted about 4 inches (10 cm) deep in well draining sandy soil in the fall, and they will grow and flower the following spring with little other care.