You might expect to find an onion in the veggie patch, but this one (Allium giganteum) is mainly used as a bedding plant for it wonderful large globular purple flowers that appear through mid summer on long stalks.
Due to their good height, they are excellent as mid or background plants when planted in groups, with other shorter colourful plants in front but avoid windy spots due to their height and weight of flower heads.
They are also good as cut flowers, making a strong shape and colour statement in arrangements.