Giant allium is the granddaddy of all allium. It is a huge variety that grows up to 6 feet tall. Giant allium blooms in May to June and has a lavender ball flower. The flower grow to the size of a softball. The seed heads make impressive displays on their own, after the florets die back. Another allium variety, White Giant, is the same size.
Globemaster is a cultivar of the giant flowering onion or giant allium. It has been improved to have a deeper purple color, longer bloom time and higher floret count. It produces a tighter ball than the giant allium. The foliage dies back on the plant as the flower blooms.
Star of Persia has the largest flower head among alliums, but it is set on stems only 2 1/2 feet tall. The flowers grow to between 8 to 12 inches across and are made up of silvery lavender florets. The flowers are spiky and looser than giant allium.
The height of this plant isn't spectacular. It only grows 2 feet high, but it carries a flower head that is huge. The flower is loose and starry with pink and green florets. The flower can be nearly a foot across. The flowers are unusual and resemble sparklers.
Ivory Queen is a white allium with 6-inch blooms. It has a compact head in a perfect round ball. The leaves are wide and blue-green. The height is medium, reaching 10 inches tall. The bright white balls show well against the unique foliage.