Allium giant onions in groups of five, seven or nine in the back of a flower border. The flowers are so striking that even a single specimen makes a good accent. To emphasize their bold form, try combining them with white-flowered perennials or gray-leaved Alliums such as lamb's ears or wormwood. Some other species of ornamental onion, shorter ones, make excellent border or rock garden Alliums; others do well in greenhouses.
Allium giant onions in a large container filled with a porous growing medium of equal parts of garden loam, coarse sand and peat moss. A commercial mix with some builder's sand or perlite added to it also works well. Allium in the fall, and keep the container in a cool spot, between 35° and 50°F. Don't allow the bulbs to freeze. See Growing Plants In Containers and Containers For Plants in Yardener’s Tool Shed.
Cutting and Drying
Giant onion flowers are excellent for indoor arrangements. Cut stems when flowers are just opening and they will last up to 3 weeks. These stunning blossoms also dry well. Pick them at their peak bloom and hang them in a warm, dry place until they are thoroughly dried. The flowers retain their color quite well. Another option is to wait until the flowers are spent and seed pods form on the stems. Harvest these dried stems with the delicate dried flower ball skeleton at this time. For more information see the files on Keeping Cut Flowers and Cut Flower Supplies. For more information see Drying Flowers and Flower Drying Supplies
Ornamental onions generously duplicate themselves by producing new bulbs as they mature over the seasons. To acquire more ornamental onion Alliums and to encourage optimum growth on existing ones, divide giant onions every three years in the fall. Alliums left in place much longer than that become crowded and have small flowers. Carefully dig up the bulb clumps, shake the soil off the roots, and put them in a basket in a shady spot to dry off for a couple of days. Then separate the offsets from the parent bulbs and Allium. Offsets bloom in 1 to 3 years.