Allium Giganteum lives up to its name with heights anywhere from 3-5 feet this Allium is a definite show stopper. Commonly called giant onion it is most likely the tallest of the ornamental onions. It’s made up of perfect little purple florets that create a large round ball on top of a sturdy stem similar to a topiary. Adding Allium to a garden will make heads turn and grab attention. The best way to plant is in large groupings for a more contemporary style or periodically place throughout a garden.