Ornamental onions or the Allium family make excellent sunny garden plants. The bulbs once planted are unharmed by moles, mice and deer. They can be used effectively in mixed flowerbeds from the back of the border up to the front, and even in rock gardens. Generally they do not need to be divided unless you want more plants. Beautiful tight balls of purple, pink or white flowers rise on generally tall, leafless stalks.
It is best to plant the bulbs in the fall in odd-numbered groups of 3 to 5 or more. Be careful not to plant too deep or they may not bloom. Use alliums to fill in the gaps between blooming periods of other flowers such as between spring bulbs and summer perennials.
Water ornamental alliums regularly when growing and blooming but cut back the water as they go dormant. After blooming alliums, like tulips, go dormant and their leaves turn yellow as they die down. Do not cut the leaves off as they supply nutrients to the bulbs for storage for next season’s growth. To hide the withering leaves combine ornamental onions with bushy plants like flax and tick seed. Also at this time scratch a little bone meal into the surrounding soil.
If you wish to divide your alliums dig up the bulbs after flowering and separate the bulblets from the main bulb. Replant and expect it to take a couple of years to reach flowering size.
If you want to cut the blooms for bouquets cut when one-third of the blooms on the ball cluster have opened. These should last for about 2 weeks. Alliums also dry beautifully, simply cut either flowers or seedheads. Cut flowers when they are fully opened and leave standing in a vase with a small amount of water until it evaporates. Cut seedheads when they are still tightly closed and hang stems upside down in a warm, dry, dark place for about a week.
Allium christophii or Star-of Persia is one of the most spectacular alliums. This giant allium flower heads are huge at 8-12 inches across, full of clusters of star like silvery-lavender flowers on stout stems about 15 inches tall, blooming in late spring.
Allium giganteum or Giant Ornamental Onion also have huge purple flowers and bloom in summer. These purple alliums grow to about 48 inches tall towering over other flowers. Allium karataviense or Turkestan Ornamental Onion are shorter at 10 inches tall, and large whitish flowerheads sit just above pruple-gray, tulip like leaves. They bloom in mid to late spring. Allium stipitatum or Persian Flowering Onion grow 24 inches tall, and have lavender, pink or red-violet flowers blooming in late spring.