'giganteum' is the tallest species of the cultivated onions.
Though valued as an edible pant in Asia, in most gardens around the world this stately bloom is only planted its their decorative blossoms.
White and purple Allium giganteum plants, photograph by F. D. Richards; CC.
Gardener's HQ Guide to Growing Giant Onion
This plant requires a medium level of maintenance to perform at its best, and is particularly suited to US zones 5-8. They prefer warmer temperatures and strong sunlight during the day.
Be sure that soil is well drained but retains a trace of moisture. This will enable the Giant onions to better withdraw the nutrients necessary for proper growth.
If correctly taken care of, these plants can grow to be between three feet and five feet (90 to 150 cm). Allium giganteum grows best when grown in groups, so be sure to arrange them in at least a group of five.
Many gardeners choose these to line their flower beds, due to their columnar nature. They are also great as cut flowers in arrangements and emit a pleasant, leafy fragrance. They add a mysterious aura to a garden and can be used to great effect.