About 400 species of alliums exist. The best-known are edible varieties, which include onions, shallots, leeks, chives, and garlic. While their savory cousins excel in the kitchen, ornamental alliums, like the Allium giganteum, shine in the perennial border. Their bold and unusual blooms adorn gardens from mid-spring through midsummer.
Although most alliums bloom in shades of purple, some varieties bear flowers of blue, pink, yellow, or white. The flower heads generally are globe-shaped and range in diameter from 3 to 12 inches. Alliums come in all heights, from 4 inches to 4 feet. Many alliums hold their bloom for as long as a month, which makes them a sought-after perennial. Some varieties are great naturalizers and will spread generously if allowed to do so.