Allium giganteum, also known as Giant Onion
They look like they’ve jumped out of a Dr. Zeus book — giant purple balls stuck like lollipops on long flexible stems. Alliums can be a bit startling the first time you encounter them. But there’s so much to love about these drought tolerant plants, including long bloom period and resistance to most pests and diseases. And, their whimsical appeal is a sure-fire way to liven up your garden.
BALLS OF FUN
Partly due to the fact that they seem to hover, alliums add a big dose of fun to almost any garden setting. Teeter-tottering over other flowers, their purple flower heads act as key accents throughout the border. In formal gardens, they inject a note of humor, while in more informal settings they make a striking statement. And they always end up forming spontaneous color combinations with other plants in the garden.
Alliums in a spring garden
We have Rosemary Verey, the famous British gardener, to thank for introducing the world to these beautiful flowers. Her Laburnum Arch at Barnsley House is today one of the most iconic garden images. Created in 1964, the arch features cascading golden chain tree flowers underplanted with thick swathes of purple alliums. The jaw-dropping combination has been reproduced in one form or another for decades.
Rosemary Verey’s famous Laburnum Walk
The allium family is a genus of flowering plants that has hundreds of species, including onions, garlic, scallions, shallots, leeks and chives. While most have been cultivated for centuries as food crops, ornamental onions are grown strictly for their decorative qualities. A word of caution: the bulbs may look like ordinary onions, but they are not edible.
Allium gigantum poking up among pink roses
Since they are spring bloomers, allium bulbs must be planted in the fall (once the soil has cooled.) I plant mine just after the leaves have fallen. Six months later in late spring, just when you’ve all but forgotten them, rosettes with giant, paddle-shaped leaves start tracing patterns on the soil surface.
Then, shortly after the leaves appear, the plant sends up a thick, leafless stem terminating in a swollen bud. The bloom slowly takes shape, revealing thousands of tiny, star-like flowers that combine to form a dense purple ball. Once formed, the flower heads are incredibly long-lasting, retaining their color for a week or more. The flowering stage continues with each plant producing one or two more blooms.
A fully developed flower head
DESIGNING WITH ALLIUMS
I plant my ornamental onions in groups of threes or fives and sow them haphazardly throughout the garden. This makes for an abstract design that combines well with both formal and informal spaces. It’s important not to plant the bulbs too close together, though, in case come spring, their spheres collide and ruin their effect.
Alliums look great with other spring flowers like peonies and irises. And the later blooming varieties make stunning companion plants to salvia, yarrow, monarda, catmint and daylilies. Alliums are not repeat bloomers, so after they exhaust themselves, they go dormant for the summer. I plant daylilies by my alliums to hide the foliage once it starts to wither.
Spring color combination with alliums
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
There are many different varieties of alliums, 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 rise to 24″ high.
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.
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.
Star of Persia is a wild-looking allium variety. It produces star-shaped fuchsia flowers on gray-green stems.
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.
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.