Perhaps the tallest of the ornamental onions, Allium giganteum is a bold and striking addition to the garden with its star-shaped, tiny lilac-purple flowers forming a 5-6 in. wide (12-15 cm) globe-shaped cluster. Blooming in late spring to early summer, this Giant Allium enjoys long-lasting blooms and remains ornamental in the garden well into summer. This bulbous perennial makes a perfect background plant that you may want to combine with finer-textured plants such as ornamental grasses.