Allium, or flowering onion, is an ornamental relative of onions and garlic. It is grown for its large orbs of small lavender flowers. Like its vegetable cousins, allium produces underground bulbs. Allium seeds are short lived, so dividing the bulbs is the preferred propagation method for the plants. They require division every three to four years, but they can be lifted more often if the bed becomes overcrowded. Propagate from divisions in fall as the plants begin to enter dormancy.
Loosen the soil around an existing allium once the foliage dies back naturally. Use a hand-held gardening fork and take care not to cut through the roots. Lift the plants from the loosened soil.
Shake the dirt from the roots. Allium roots have a thickened central root, or bulb, with several smaller roots growing from each.
Tease apart the bulbs and stems with your fingers. Divide each plant into two or three new plants, depending on the size of the root system.
Inspect the bulbs for damage or soft spots indicating rot. Dispose of any damaged or diseased bulbs.
Replant the bulbs into a full-sun, well-drained garden bed immediately after dividing. Plant each bulb so the top is 4 inches beneath the soil surface. Space bulbs 6 to 8 inches apart in all directions.
Cover the bulbs with a 2- to 3-inch layer of mulch to prevent soil heave from frost and thaw cycles in winter. New plants begin growing from the division in spring.