How to Grow Alliums (Ornamental Onions), a Cottage Garden Favorite
What are Ornamental Alliums?
Ornamental alliums are related to onions and look a great deal like them. They grow from bulbs which look and smell like onions. The plants have strappy foliage like onions. The biggest difference is the size of the plants and their flowers. Depending on the variety they can grow to 3 feet high with flowers the size of baseballs like the famous Globemaster allium (Allium giganteum). Other varieties are shorter with flowers that droop (A. cernum or nodding alliums) or have stringy petals (A. schubertii or hair allium) which look like fireworks to me. My personal favorite are the (A. sphaerocephalon) with smaller flowers that look to me like eggs. drumstick allium
How to Grow Ornamental Alliums
Alliums are native to the Northern hemisphere so they have a large hardiness range from USDA planting zone 3 through 9. Most ornamental alliums are hardy from zones 4 through 8. They are planted in the fall after the weather and soil cools but before the soil freezes. Planting your allium bulbs before the ground freezes gives them a chance to grow some roots and get established before winter sets in and they become dormant. Then in the spring, as soon as the soil warms, they will be ready to grow and flower.
The rule of thumb for planting depth is three times as deep as the width of the bulb. So if you have a bulb that is 2 inches wide, you should plant it 6 inches deep. Plant the bulbs like you would onions, with the roots pointing down and the pointy end from where the leaves will grow, pointing upwards.
Since each plant has only one flower, plant the bulbs in groups like you plant your tulips and daffodils instead of singly. A single ornamental allium looks lonely. A clump of them can take your breath away.
Ornamental alliums should be grown in full sun and in well-drained soil. They aren't susceptible to many diseases or pests but they are sensitive to moisture and the bulbs will rot in soggy soil. Speaking of pests, all allium are deer and rabbit resistant. Deer and rabbits don't care for their onion taste or smell. Great news for those of us who share our yards and gardens with hungry deer.
Depending on the variety alliums can bloom in the spring (large globe allium) or summer (drumstick, nodding and hair allium). There is no need to deadhead them. They only bloom once. The flowers can be left on the plants when they are exhausted. The seedheads are attractive and can be used in dried arrangements. Keep watering the foliage to keep it alive and making food for the bulb which will be stored for next year's foliage and flowers. In the fall, the foliage will die. Remove it from your garden so that harmful insects can't hibernate over the winter in the debris.
How to Divide Ornamental Alliums
Every 3 or 4 years, you will notice that your alliums aren't blooming well. They are telling you that it's time to divide them. Carefully dig up the bulbs and separate the bulblets on the sides. Replant the bulbets in another area of your garden until they have reached blooming size in a year or two. Then you can transplant them back into your garden to add to your display.
How to Grow Ornamental Alliums From Seed
You can grow ornamental alliums from seed, but it will be at least two years before the plants bloom because they have to form their bulbs first. Start your seeds indoors 6 to 8 weeks before your last frost. Plant them 1/4 inch deep in containers filled with pre-moistened soil. Germination should occur in 7 to 10 days. You can transplant your seedlings into your garden after your last frost.
© 2014 Caren White