They look like they hopped out of a Dr. Zeus book — bright purple balls stuck like lollipops on tall, sturdy stems. Ornamental onions (alliums) can be startling the first time you see them. That said, there’s so much to love about these magnificent plants, including long bloom period and resistance to most pests and diseases. And their curious appeal can really liven up a garden.

BALLS OF FUN

Why be so serious? Often it’s the unexpected that makes life so interesting. And without a doubt, ornamental onions were born to surprise. In formal landscapes, they inject a note of humor, while in informal ones they’re electrifying. And each year as their numbers grow, they form new, unexpected color combinations with other flowers in the garden.

Alliums in one of my spring gardens

Be that as it may, alliums are a relatively recent addition to the garden. In fact, they were virtually unheard of until the English garden designer Rosemary Verey, introduced them into one of her designs. Created in 1964, her jaw-dropping Laburnum Arch brought ornamental onions into the international limelight. Ever since, their popularity has only continued to grow.

Rosemary Verey’s famous Laburnum Walk

ABOUT ALLIUMS

Ornamental onions are part of the allium family, a large genus of plants that includes onions, leeks, scallions, garlic and chives. Unlike their edible cousins, however, they are cultivated solely for their flowers. Among the hundreds of species available, there are some that grow to 6 inches, while others reach as high as 4 feet. Their purple, pink or white blooms can be ball-shaped, star-shaped or pendulous. And some resemble exploding fireworks. 

Botanical Gardens in Gothenburg,Sweden/Photo: shutterstock 

Ornamental onion bulbs must be planted in the fall (at the same time as daffodils and tulips.) Most species make an appearance in late spring, when giant, paddle-shaped leaves start popping up on the soil surface. Eventually, the bulb sends up a thick, leafless stem topped by a single, swollen bud.

Over time, the bud slowly expands to reveal hundreds of tiny, star-like flowers that gradually combine to form a dense purple ball. By mid-June, many plants produce one or two additional blooms.

A fully developed flower head

DESIGNING WITH ALLIUMS

Ready to give ornamental onions a try? I say do like Rosemary Verey and go big. For the most impact, I sow my alliums in groups of threes or fives haphazardly throughout the garden. Alliums make great companions plants to other spring flowers like peonies and irises. And the later blooming varieties look great with salvia, yarrow, monarda, catmint and daylilies.

One of my designs combining alliums with pink azaleas and green hostas 

All allium varieties flower best in full sun, although they’ll also grow in semi-shade (see above.) Once the flower has died, cut the stalk down to refocus energy back into the bulb. Dried flower heads make great additions to indoor flower arrangements, by the way.

POPULAR ALLIUM VARIETIES

As I mentioned before, there are literally hundreds of allium varieties available. But, here are some of the most popular:

Purple Sensation, the earliest bloomer of all the large-flowered alliums, flowers in late spring. The variety makes a stunning companion to peonies, bearded irises and delphiniums. The 4″ to 6″ diameter violet globes float on sturdy stems that grow to 24″ high.

 ‘Purple Sensation’

If you’re looking for a big ‘wow’, try Globemaster and/or Gladiator. The tallest of the ornamental onions, these varieties boast huge purple flower heads (some measuring as big as 8″ to 10″ across) on 3 to 4-foot stems. A white version called Mount Everest is slightly shorter.

‘Globemaster’

‘Mount Everest’

Adorable Drumstick produces reddish purple cone-shaped flowers (like drumsticks) in July and is a great companion to other summer-blooming plants like daylilies, daisies, and coneflowers.

‘Drumstick’ 

Star of Persia (Allium christophii) is a wild-looking allium variety. It produces star-shaped fuchsia flowers on gray-green stems and blooms late spring to early summer.

Star of Persia/Allium Christophii

If you’re looking for real fireworks in the garden, try Schubert allium whose pink umbels look like an explosion. Seed heads look great in the garden, too, long after the blooms have faded. Blooms late spring to early summer.

Allium Schubertii

In addition to these great cultivars, there are lesser-known allium varieties that can keep the blooms going all through the summer. For more information on these as well as a great video on how to plant them, click here for Fine Gardening’s excellent article on these summer beauties.

To see photos of my garden designs, including plant lists, check out my Instagram at carole.herebydesign. I post seasonally from spring through fall.