Growing Alliums: The Ornamental Onions

Add Alliums to Your Garden

Every fall, I am seduced into planting more bulbs. After 30 years, you would think I couldn’t possibly need any more daffodils—and I really don’t—but that doesn’t stop me from planting more!

When it comes to bulbs, you have a lot to choose from. A favorite category of mine happens to be the ornamental onions (alliums). 

Distant cousins of edible alliums such as onions and garlic, there are over 700 species of ornamental onions. Some are tiny—reaching only 6 inches high—while others grow to be over 5 feet tall! Some have nodding, bell-shaped blossoms, while others look like bursts of fireworks.

Then there are the huge, round flowerheads that resemble chive blossoms on steroids! The blooms tower high in the air and wave globes of color at the end of long, slender stalks. Most alliums bloom later than the spring bulbs so if you need an exclamation point of color to carry your garden from daffodils to peonies, look for an allium.

Alliums look awesome on their own, or great when planted by the dozens. They are perfect for a naturalistic planting scheme.

See this video to enjoy their beauty and range:

Deer- and Rodent-Resistant

Since they are in the onion family, rodents, rabbits, and deer tend to leave them alone, repelled by their strong flavor. In fact, a ring of allium around more vulnerable plants might serve to protect them from grazers.

However, the flowers don’t smell “oniony” at all; most are quite pleasantly fragrant and are a favorite of bees and other pollinators. Although their leaves and stems give off an oniony scent when bruised, most allium flowers are sweet-scented. They make long-lasting cut flowers and can be dried as well.

Best Allium Varieties

Most often, ornamental alliums bloom in rich pinks and purples, but some are creamy white (A. neapolitanum), sky blue (A. caeruleum), and sunny yellow (A. moly). Although most form globes of clustered flowers, others, such as A. siculum, A. triquetrum, and A. cernuum (a North American native), droop demurely.

Here are some common varieties of alliums, ranging from small to tall. I wish I had photos for them all!

• One of the tiniest charmers is dwarf Allium oreophilum, growing only 3-6 inches tall. It bears loose clusters of rose-colored, fragrant flowers.
• Nodding onion (A. cernuum) is a North American native with bell-shaped flowers that hang from its 6-8 inch tall stems. Perfect for a sunny rock garden, they come in shades of purple and pink along with white.

• Golden garlic (A. moly) ‘Jeannine’ bears 2 to 3 inch wide clusters of yellow star-like flowers on 8 to 10 inch tall stems above its blue-green leaves. A native of southern Europe, it was considered a sign of prosperity and good luck. A. moly blooms profusely, doesn’t mind a bit of shade, and naturalizes well. At less than a foot tall, it’s good for a rock garden or in beds and borders. (A. flavum is yellow, too, and taller, with bell-shape florets.)

• For a true blue lollypop try A. caeruleum. A Siberian native, it has 1-2 inch wide densely packed round blossoms and grows 12-18 inches tall.
• Sweet-scented A. neapolitanum, aka the bride’s onion, bears pure-white, star-shape flowers forming loose umbels. It’s about a foot tall and needs full sun, but lacks winter hardiness, becoming perennial only in Zones 7 and 8. A. roseum has much the same form, but its flower heads are pink.
• For something a little different, look for A. schubertii. It looks like a 4th of July sparkler with a huge starburst of tiny pink blossoms. It also grows 12-18 inches tall.

• Star of Persia (A. christophii) has a huge flower head consisting of up to 100 individual pinkish-purple flowers that can be 8 to even 10 inches across. It grows 18 to 24 inches tall.
• Drumstick alliums (A. sphaerocephalon) are maroon-red balls of flowers on 20 to 24 inch tall stems. They grow to 2 feet tall and naturalize easily in Zones 4 to 10. Fragrant and distinctly percussive-looking, they make an interesting statement in the garden or vase.
• Looking like a dark red Queen Anne’s lace, A. atropurpureum is an eastern European native that grows 20 inches tall.
• Commonly called ornamental garlic, A. aflatunense is one of the loveliest species. Dozens of small, star-shape flowers form a lilac-purple globe, which rises about 10 inches above narrow blue-green leaves. Native to Iran, ‘Lucy Ball’ and ‘Purple Sensation’—two aflatunense hybrids—are deep, dark purple and naturalize well in the garden.

• Tired of purple? ‘Mount Everest’ is a pure white allium with 4-6 inch wide flowers that look like giant snowballs. It grows 3 to 4 feet tall. ‘White Giant’ has even larger flowerheads on 3 to 4 feet tall stalks.
• A. azureum, or blue of the heavens, is a true cornflower-blue and grows up to 2 feet tall.
• Surely the biggest is the aptly called giant onion, A. giganteum. As its Latin name says, these are the big guys. Shooting up to 6 feet tall, they have gray-green leaves and bear big, round, deep purple flowerheads 5 to 10 inches across.
• The best allium to grow in pots is A. karataviense. Although only 8 to 10 inches tall, it has 4-inch, slightly scented blossoms. It usually flowers in pink and pale lilac shades.
• ‘Globemaster’, a hybrid, bears deep-violet, 6- to 8-inch, globe-shape flower heads and grows 3 to 4 feet tall.
• ‘Gladiator’ grows to be 3 to 5 feet tall and has soft-ball sized rosy-purple flowers.
• ‘Summer Drummer’ is the tallest hybrid at 4 to 6 feet tall. It has baseball-sized flowers with a mix of purple and white florets.

Allium Planting and Growing Tips

Planting and caring for allium couldn’t be easier:

• All alliums like rich, well-drained soil and prefer a sunny site—although many species will also tolerate shade!
• The best time to plant the bulbs is when they’re dormant in the fall. In fall, set all but the largest bulbs 4 inches deep; set the giants 8 inches deep—measured from the base of the bulb.
• Plant alliums throughout the garden in clusters—standing alone, they tend to look odd. The best effect is gained by planting a clump of bulbs—three to five spaced well apart for large alliums or a group of 10 to 15 for smaller species.
• If you’re looking for good companion plants, alliums look great among mounding perennials such as lady’s mantle, true geraniums, irises, or sedums. Hostas, silver-leaved artemesias, and peonies also make good companions. These will help to hide the alliums’ foliage, which tends to get brown by the time they flower.
• Add compost around new shoots in the spring.
• Stake taller varieties to support the blooms.
• Feed in early summer with a liquid fertilizer. 
• The bulbs are long-lived and multiply readily. Most will naturalize in Zones 4 to 8, and they bloom on a most timely basis, in May or June or even July, between the carnival of spring bloom and the full flowering of summer.
• As allium fade into seed heads, they add a subtle beauty all their own.
• Cutting advice: For indoor arrangements, cut alliums when the flower heads are just one-quarter open. Any faint oniony scent released by cutting the stems will disperse as soon as you put them into water.

When you are bulb shopping this fall consider adding a showstopping giant allium or a delicate-looking dwarf to your garden!