Few spring-flowering bulbs make quite the statement of ornamental alliums. Their great globes of purple, lavender, pink, white, and occasionally yellow seem to hover above the garden on remarkably straight stems. Some are modest little plants suitable for the front of a border; others produce flower heads the size of softballs—or larger—standing three or four feet above the ground.
Better still, ornamental alliums are generally easy to grow, return year after year when properly situated, attract pollinators, and are usually passed over by deer and rabbits. For a gardener who wants considerable effect without considerable fuss, they earn their keep.
What Are Ornamental Alliums?
Alliums belong to the same genus as onions, garlic, chives, shallots, and leeks. The genus Allium contains hundreds of species native across much of the Northern Hemisphere, with particularly rich diversity in Europe, Asia, the Middle East, and western North America.
The ornamental varieties are grown primarily for their flowers rather than their usefulness in the kitchen. Their family resemblance is nevertheless easy to discover: bruise a leaf or cut into a bulb and the familiar onion or garlic scent usually gives the game away.
The flowers are composed of dozens—or sometimes hundreds—of tiny individual blossoms arranged in rounded umbels. From a distance, the effect is that of a single great ball of flowers.
Why Grow Ornamental Alliums?
Their chief virtue is architectural form. Tulips and daffodils make broad sweeps of spring color, while alliums introduce strong vertical lines and nearly perfect spheres.
They are especially valuable because many varieties bloom during the transition from the main spring bulb season into the early perennial season. Just as the tulips are beginning to bow out, the alliums can take the stage.
Alliums also have several practical virtues. They generally prefer ordinary garden conditions, need little attention once established, provide nectar and pollen for bees and other insects, and their onion-scented foliage and bulbs make them relatively unattractive to browsing deer, rabbits, and many rodents.
Even after flowering, the dried seed heads remain handsome. Left standing among perennials and ornamental grasses, they can provide structure well into summer.
When Should Allium Bulbs Be Planted?
Plant ornamental allium bulbs in autumn, generally from September through November, depending upon your climate.
The important thing is to get them into the ground after the soil has begun to cool but before it freezes hard. They need the winter chilling period to establish roots and prepare for spring growth.
In warmer Southern gardens, there is seldom any reason to rush. October and November are often excellent planting months, and planting may continue into early winter where the ground remains workable.
If bulbs arrive while the weather is still quite warm, keep them cool, dry, and well ventilated until planting time. Do not seal them in plastic where moisture can accumulate.
Choosing the Right Location
The ideal allium site has full sun and excellent drainage.
Most ornamental alliums perform best with six or more hours of direct sunlight each day. A little afternoon shade may be tolerated in hot climates, but deep shade usually produces weaker plants and poorer flowering.
Drainage is more important than rich soil. Allium bulbs dislike sitting in cold, wet earth. Heavy clay that remains waterlogged through winter can cause bulbs to rot.
If your garden has poorly drained soil, amend it with organic matter where appropriate or plant alliums in raised beds or naturally elevated areas. Avoid low spots where winter rain collects.
A well-drained sandy loam is close to ideal.
How Deep Should You Plant Alliums?
A useful old bulb-planting rule works well: plant the bulb about two to three times as deep as the bulb is tall.
Large ornamental allium bulbs are commonly planted about 6 to 8 inches deep, while smaller species may need only 3 to 4 inches.
Place the bulb with the pointed end upward. If you genuinely cannot tell which end is which, plant it on its side. The emerging shoot is quite capable of finding daylight without our assistance.
Space large alliums roughly 6 to 12 inches apart, depending upon the variety and the effect desired. Smaller species can be planted much closer together.
For the best display, resist the temptation to plant solitary bulbs at regular intervals like fence posts. Alliums usually look better planted in groups or loose drifts.
Designing With Alliums
This is where alliums become especially useful.
Large varieties are superb rising through lower-growing perennials. Their stems are sufficiently narrow that they do not create a heavy visual barrier, yet the flower heads appear above neighboring plants like purple punctuation marks.
Try them among catmint, hardy geraniums, salvias, peonies, roses, lamb's ear, daylilies, or ornamental grasses.
Companion planting also solves one of the few aesthetic shortcomings of the large alliums: their foliage often begins to yellow before the flowers have finished blooming.
This is perfectly normal.
Planting alliums among leafy perennials conceals the declining foliage while allowing the flower stalks to rise above it. It is a far better solution than cutting the leaves prematurely.
Don't Cut the Leaves Too Soon
As with daffodils, tulips, and other bulbs, the leaves manufacture and store the energy needed for next year's flowers.
After flowering, allow the foliage to yellow and die naturally before removing it.
The flower heads are another matter. You may cut them after bloom if you prefer a tidy garden, but there is no necessity to do so. Many gardeners deliberately leave the dried globes standing because they remain striking long after their color has faded.
Some are excellent in dried arrangements as well.
Watering and Feeding
Newly planted bulbs should be watered after planting to settle the soil and encourage root development.
Once established, ornamental alliums are fairly drought tolerant. During active spring growth they appreciate reasonable moisture, but constantly wet soil is considerably more dangerous than occasional dryness.
In ordinary fertile garden soil, elaborate feeding programs are unnecessary. A light application of compost or a balanced bulb fertilizer in spring can be useful where soil is poor.
Avoid excessive nitrogen. You are trying to grow flowers, not exceptionally luxurious onion leaves.
Some Alliums Are Giants—and Others Are Not
The word "allium" sometimes brings to mind enormous purple globes, but the genus offers much more variety.
Allium giganteum is among the famous tall types, producing large purple flower heads on imposing stems.
'Globemaster' is celebrated for its enormous violet-purple globes and makes an extraordinary specimen in the perennial border.
'Purple Sensation' is somewhat more restrained and extremely useful for mass planting, producing rich purple spheres in late spring.
'Mount Everest' provides the same strong architectural form in white.
At the other end of the scale are smaller ornamental alliums that work beautifully in rock gardens, along paths, and toward the front of borders. Some naturalize readily and gradually form attractive colonies.
There are even yellow-flowering species, such as Allium moly, which bear cheerful clusters of star-shaped flowers rather than the enormous purple spheres associated with the better-known ornamental hybrids.
Do Alliums Come Back Every Year?
In a suitable climate and well-drained soil, many ornamental alliums are reliable perennials.
Some gradually multiply by producing offsets around the original bulb. After several years, crowded clumps can be lifted and divided when dormant.
Performance varies by species and climate, however. Certain spectacular hybrid alliums may persist for years without spreading aggressively, while smaller species may naturalize with enthusiasm.
Good drainage is usually the difference between an allium that settles down for a long residence and one that quietly disappears.
Deer, Rabbits, and Pollinators
Alliums offer an unusually agreeable combination for the garden.
Bees and other pollinating insects are strongly attracted to the flowers, while deer and rabbits generally dislike the onion-like compounds in the plants.
No plant should be advertised as absolutely deer-proof—deer have been known to revise the gardening books when sufficiently hungry—but alliums are among the better choices for gardens troubled by browsing animals.
This also makes them useful companions for more vulnerable spring bulbs.
Growing Alliums in Containers
Ornamental alliums can also be grown successfully in pots.
Choose a substantial container with excellent drainage and use a free-draining potting mixture. Large varieties need enough soil depth to accommodate their sizeable bulbs and tall stems.
They can be planted alone or incorporated into layered bulb containers with tulips, daffodils, crocuses, or other spring bulbs.
Remember that containers expose bulbs to greater temperature fluctuations than garden soil. In very cold climates, pots may require winter protection.
A Flower With an Old-World Character
There is something both formal and whimsical about ornamental alliums. Their geometry would be perfectly at home in an old European garden, yet those improbable spheres hovering over a perennial border have an almost modern appearance.
That combination is part of their charm.
Plant a few among established perennials and they provide accents. Plant dozens and they create a remarkable spring spectacle. Mix varieties of different heights and flowering times, and the display can continue for weeks.
Most importantly, they ask remarkably little in return: sun, well-drained soil, autumn planting, and enough patience to leave the foliage alone until it has finished its work.
Give them those things, and ornamental alliums will rise each spring like brightly colored globes above the garden—orderly, architectural, and just eccentric enough to keep things interesting.
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