This hybrid from Allium guru Mark McDonough was picture perfect in our trials. 'Millenium' forms a compact, upright clump of glossy green, thick and strappy leaves which emit a slight smell of onion when crushed.  In late July and August here in Michigan, a profusion of large 2”, bright rosy purple, tightly rounded clusters of flowers appear on strong stems just above the attractive foliage.
Alliums are charming plants for the rock or herb garden. When the foliage is bruised, it smells like onions since they are in the onion family. Butterflies and honeybees adore the flowers' sweet nectar but deer and rabbits steer clear of this perennial beauty.
 
 
Allium 'Millenium' is very easy to grow in full sun to part shade.  It will tolerate soil of any fertility and will grow in clay soil.  This selection has not been known to reseed and is not invasive.  It may be propagated in fall by digging it up and dividing the rhizome with the bulblets attached.  Allium is typically pest and disease free.  Its aromatic foliage also makes it deer and rabbit resistant.
 
From Walters Gardens website https://www.waltersgardens.com/variety.php?ID=ALLMI