GET GROWING: Amazing Alliums: how to plant and grow ornamental onions

With the arrival of October, it’s time to get serious about planting bulbs. In my garden I plant different flower bulbs in autumn; everything from ornamentals like tulips and daffodils to edibles like garlic and shallots, but my favorite bulbs to plant are alliums. Alliums, AKA ornamental onions, are incredibly showy plants, with most species producing rounded flowers in shades of purple, violet, pink, yellow, or white.

Ornamental onions are not only beautiful plants, they are easy to grow, reliable and, thanks to their strong smell, resistant to pests such as deer, squirrels and rabbits. When in full bloom they attract pollinators and bees and when the flowers fade the seed heads still look great in the garden.

The best location for alliums is one with plenty of sun and well-drained soil. Plant the bulbs in the garden in late October, about four to six weeks before the ground freezes. It is important to plant the bulbs at the right depth. Since spring onions can vary in size from species to species, the rule of thumb is to plant them at a depth of three times their diameter. For example, an allium bulb two inches in diameter should be planted six inches deep.

In spring, fertilize flower bulb beds with a 3 cm layer of compost and an organic flower fertilizer. Most alliums flower from late spring to early summer and when the flowers are wilting, be sure to leave the seed heads in the garden. Not only are they conspicuous, but they also provide seeds for birds.

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Spring onions are available at local garden centers as well as online. A little research will help you choose the best alliums for your garden. Here are five of my top allies:

Allium sphaerocephalon

Better known as Drumstick Allium, this hardy onion produces slender stems topped with green and purple ovate flowers in early to mid-summer. Plant in clusters of at least five to seven bulbs and tuck them between perennials such as ornamental grasses, sage, euphorbia, verbena, speedwell, and perennial geranium. With any luck they will naturalize and you can divide the clump every few years and add these pretty alliums to your garden.

Leek ‘Globemaster’

Allium ‘Globemaster’ is a show-stopper with large rounded flower clusters full of small, star-shaped flowers. This allium produces some of the largest buds, with these buds reaching between 8 and 14 inches in diameter. Maximize the visual impact of ‘Globemaster’ by planting the bulbs in groups of at least three to five plants.

Allium schubertii

This unique allium produces short stalks 30 to 40 centimeters tall and massive, purple colored flowers that can spread up to 40 centimeters wide. Think about it, a flower 40 centimeters in diameter! Unlike many alliums, this species does not have perfectly round flowers. Instead, it resembles an exploding firework of small, star-shaped flowers on different-sized flower stalks. Once the flowers wither, I leave the seed heads in the garden, where they will provide interest for months.

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Allium nectaroscordum is a summer flowering ornamental onion with beautiful, bell-shaped flowers.  It is deer and squirrel resistant and blooms for weeks.  -Niki Jabbour
Allium nectaroscordum is a summer flowering ornamental onion with beautiful, bell-shaped flowers. It is deer and squirrel resistant and blooms for weeks. -Niki Jabbour

Leek Nectaroscordum

Also known as Sicilian honey garlic or honey garlic, these unusual alliums bloom in early summer, attracting native bees and pollinators. It’s a stunning plant with stems that grow two to three feet tall and are topped with pendulous clusters of small bell-shaped flowers. The creamy vinous flowers have a striped appearance and if you let the seeds set in the garden they often overgrow.

Allium giganteum, also known as giant onion, is a showy garden plant that blooms in June with round purple flowers that persist for weeks.  -Niki Jabbour
Allium giganteum, also known as giant onion, is a showy garden plant that blooms in June with round purple flowers that persist for weeks. -Niki Jabbour

Leek giganteum

This classic ornamental onion, commonly referred to as giant onion, is popular for its reliability, hardiness and its deep purple flowers, which are 12 to 15 centimeters in diameter. The stems are tall and straight, reaching a height of up to 150 centimetres, with the flowering period starting in June and lasting for weeks.

Niki Jabbour is the author of four bestsellers including her latest book, Growing Under Cover. She is a two-time winner of the American Horticultural Society Book Award. Find them on SavvyGardening.com and on social media.

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