2016: Year of the Allium
Ornamental alliums have so many good things going for them that it’s a wonder they’re not more widely planted. But alliums are definitely on the rise. They seem to be popping up everywhere: in gardening books and magazines, on Pinterest boards, and in public and private gardens across the country.
Most allium flowers have a long, leafless stalk topped with a globe-like bloom that’s made up of a cluster of individual florets. Like exclamation points, alliums stand out from other plants, adding emphasis and excitement wherever they’re grown.
In recent years, alliums have been used to great effect in the naturalistic plantings of garden designers such as Piet Oudolf and James van Sweden. They are ideal companions for ornamental grasses and other low maintenance perennials such as sedum, rudbeckia, echincacea and salvia.
Deer are another reason alliums are increasingly popular. Some gardeners fight a daily battle with roving bands of deer that will munch on anything green. Alliums are on the short list of plants deer tend to avoid. In the garden, the plants are odorless, but step on them or chew on them and the cell walls break, releasing volatile, sulfur-based chemical compounds that have a pungent odor and bitter taste.
These sulfurous compounds, classified as secondary metabolites, are a defense mechanism against diseases and insects as well as predators. This makes alliums virtually bulletproof. And, though the foliage repels, the flowers are filled with sweet nectar that’s highly attractive to honeybees, bumblebees and other pollinators.
Edible alliums are among the world’s oldest cultivated plants, but there is no record of them being used as ornamentals until plant hunters began collecting alliums in the mid-1800s. Another 150 years passed before the horticultural world started to fully appreciate their garden potential.
Alliums are members of the onion family, which is a big one and has more than the usual number of taxonomy problems. Formerly classified as alliaceae, they are now amaryllidaceae, subfamily allioideae. Experts are unable to agree on the number of species, with estimates ranging between 500 and 750.
Like their culinary relatives, garlic and shallots, most ornamental onions grow from bulbs. Planted in fall, they bloom from late spring to early summer. The flowers have hollow stems that rise above strappy basal leaves. As with other spring-blooming bulbs, the foliage begins to wither away shortly after or sometimes even while the flowers are blooming. Though the foliage isn’t around for long, it’s enough to give the bulbs the energy they need to return and flower year after year.
The most popular ornamental alliums are grown from fall-planted bulbs, and the showiest of these are the big-headed ones such as ‘Gladiator’ and ‘Globemaster’. Alliums are native to mountainous regions in Central Asia, where winters are cold, summers are hot, and the soils are thin and porous. This gives them a tolerance, and even a preference, for dry growing conditions – ideal credentials for today’s water conscious landscaping.
The most widely planted ornamental allium is also the earliest bloomer: A. aflatunense ‘Purple Sensation’. The 3-inch diameter, raspberry-purple flower heads are displayed on 24 to 30-inch stems. The flowers last for up to 2 weeks and are excellent cut flowers.
Blooming just after Purple Sensation are ‘Gladiator’, ‘His Excellency’ and ‘Globemaster’. With blossoms that measure 5 to 10 inches across on 3 to 4-foot stems, these alliums are always impressive and their big seed heads are attractive long after the color is gone.
Several other fall-planted alliums deserve mention. Elegant ‘Mount Everest’ has pure white, 5-inch diameter flowers. Along with the misleadingly named A. nigrum (black onion) they are must-haves for any all-white garden. Possibly the most unusual-looking allium is A. schubertii (tumbleweed onion), with flower heads that look like they were caught mid-explosion. Three equally appealing species are maroon A. atropurpureum (purple-flowered onion) starry-eyed A. christophii (Star of Persia) and the two-toned drumstick allium, A. sphaerocephalon.
Ornamental alliums that grow from bulbs may produce the most dramatic flowers, but small-headed alliums have their own appeal. The flowers of these plants emerge from a dense clump of roots and have foliage that stays green and lush all season long. Bloom time for these non-bulb alliums starts in early summer and, depending on the species, can extend right through October.
One of the best of these clump-forming allliums is ‘Millenium’, a hybrid of A. nutans (Siberian chives). The purple, 2-inch diameter flowers bloom in midsummer on stiff, 15-inch stems that rise above a tidy clump of foliage. The blossoms last for weeks and are excellent for cutting. Two other summer bloomers are ‘Sugar Melt’, with light pink flowers and ‘Summer Beauty’, with lavender-pink flowers.
Two others in this group are worth noting. Allium tuberosum is both edible and very ornamental. In herb gardens it’s known as garlic chives, but in the flower gardens it’s a late summer star, with pure white flowers on 20-inch stems. A. thunbergii ‘Ozawa’ (Japanese onion) is the last allium of the season, and its orchid pink flowers are an important nectar source for pollinators who are still foraging in late fall.
In addition to this list of garden-worthy alliums, there are also about 100 more species that are native to North America. The most commonly available are Allium cernuum, also known as the nodding onion, A. stellatum (prairie onion), A. unifolium (American garlic) and A. amplectens (narrowleaf onion).
Note that some types of alliums have made their way onto noxious weed lists as they can self-sow prolifically. Species to keep your eye on include A. triquetrum, A. moly, A. neapolitanum and A. flavum.
How to Grow and Use
Alliums are tough, cold tolerant plants and most will grow in hardiness zones 3 to 9. As a general rule, they are not fussy about soil, though the ones with large bulbs require good drainage. They are also practically immune to disease and insect problems, and are rarely bothered by rodents or deer.
Alliums offer so many different flower sizes, heights and bloom times, that it’s easy to incorporate them into almost any sort of garden or landscape. Plant a variety of different species to enjoy a succession of blooms all season long.
For ornamental alliums that grow from bulbs, fall is the proper planting time. Like other fall-planted flower bulbs such as tulips, these alliums look best planted in groups; the smaller the bulb, the more you should plant in each group. The bulbs can be tucked in almost anywhere, because their foliage will die back a couple weeks after they flower. In fact, it’s best to have other plants nearby to help cover the fading foliage.
The clump-forming alliums can be planted anytime during the growing season. They are easy to divide and don’t mind being transplanted, so make good pass-along plants. You can keep these plants looking tidy and minimize re-seeding, by cutting off the flower stalks after they finish blooming.
Want to join the Million Pollinator Garden Challenge
to support pollinators? Plant alliums! Their nectar-rich flowers are highly attractive to honeybees, bumblebees and many other native bees. From May-blooming Allium karataviense
(Kazakhsatan onion) to October-blooming Allium thunbergii
‘Ozawa’, alliums will keep your yard blooming and buzzing all season long.
The National Garden Bureau recognizes and thanks Kathleen Laliberte from Longfield Gardens as author and contributor to this fact sheet.
This fact sheet is provided as an educational service of the National Garden Bureau. There are no limitations on the use. Please credit the National Garden Bureau.
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