Each year the National Garden Bureau declares a “year of” that features four plants: one vegetable, one perennial, one annual, and one bulb. We looked at the Year of the Carrot , the Year of the Begonia and the Year of the Delphinium over the last two months. Now let’s take a look at this year’s bulb, the allium, and more specifically, the ornamental varieties of allium.
Alliums: So Much to Consider!
This is the first time the National Garden Bureau has included a bulb in its Year of the program and I think their first choice of a subject was a very ambitious one. The genus Allium is huge, one of the largest in the plant world, with over 750 species. The genus is now included in the Amaryllidaceae (amaryllis family), but your older gardening books will still show it in the Liliaceae (lily family). It is best known for its edible species, including onions (Allium cepa), garlic (A. sativum), chives (A. schoenoprasum), shallots (A. cepa aggregatum) and leeks (A. ampeloprasum), but in fact all alliums are edible, most having a pungent taste and sulfury smell reminiscent of onion and garlic. Their pungent scent wards off many pests, including deer and rabbits.
Don’t expect ornamental onions to stink up your garden, however. Their characteristic oniony odor is only given off when the plant tissues are damaged in some way. Most ornamental onion flowers are unscented or even give off a pleasant scent.
What Is an Allium?
Most alliums are native to temperate regions of the Northern Hemisphere, although a few species have crossed the Equator and are found in Africa and South America. They are herbaceous perennials and most are relatively small, from 2 inches to about 5 feet tall (5 to 150 cm). They typically grow from an underground bulb that can be small or large, although some species only show a thickened stem at the base (think of the leek) while a few have tuberous roots.
The flowers are borne on umbels that are usually rounded although sometimes dome-shaped. The 6-tepaled flowers can be upright or pendant. They readily attract butterflies, bees, and other pollinators to the garden. Among flower colors, violet hues dominate, but many species have white flowers and some species have pink, yellow or blue ones.
The flowers produce capsules of black seeds. The flowering stem may persist after seeds ripen and often has an ornamental effect. You can leave them standing in the garden or harvest them for use as dried flowers.
Several species carry bulbils in their umbel, either occasionally or frequently. These fall to the ground at maturity, giving the plant a secondary means of reproduction. Some alliums in fact no longer produce seeds at all, but rely entirely on their bulbils for multiplication.
The leaves of most species are basal, but a few bear leaves on the flower stem. They are generally deciduous – indeed, they often disappear while the plant is blooming! – but are evergreen in some species. Each plant can have from one to 12 leaves and the leaf shape varies considerably, from lanceolate to tubular and even elliptical.
Growing Ornamental Alliums
In general, alliums are easy to grow, being cold-resistant (most are hardy to zone 4) and tolerant of most growing conditions. Full sun is generally best, but most will also usually tolerate partial shade and a few species grow naturally in forests and will tolerate deep summer shade as long as they grow under deciduous trees where they can get considerable spring sun. Just about any well-drained soil will do, be it rich or poor, acid or alkaline, loamy, sandy, clay or stony.
There is such a variety of shapes, colors, size and flowering periods in the genus Allium that it’s easy to incorporate them into almost any garden. By planting a variety of alliums with different flowering periods, you can ensure a non-stop succession of allium flowers from mid-spring until late fall.
Most ornamental alliums are sold as dried bulbs and sold in the fall. They are then planted as you would plant a tulip or narcissus, placing the at a depth equal to about 3 times its height. Squirrels and other digging pests are repelled by their odor and will leave them alone. Bulbous varieties bloom from mid-spring to mid-summer, depending on the species, and then go dormant until the following spring.
Other ornamental alliums have no notable bulbs and grow instead in dense clumps. These varieties remain in full growth all summer long and are best seen as perennials rather than bulbs. They are sold in pots between spring and fall and are planted as you would any other perennial, at the same depth they were in the original pot. Some clumping alliums bloom in late spring, but most are summer or fall bloomers.
A Few Notable Varieties
There is such a wide choice of ornamental alliums that it would be impossible to present them all here. I’ve concentrated on some of the showier varieties, presenting them more or less according to the order in which they bloom. Note the indication “bulb” below indicates varieties sold in the fall as dried bulbs and “clumping”, those that are sold spring through fall in pots.
A. karataviense (Turikstan allium)
This is probably the earliest of the ornamental onions, in bloom in mid-spring, at about the same time as many tulips. It produces 2 or 3 broad leaves with a bluish tint and a ball of purplish flowers (more rarely white) on a short thick stem. 10-12 inches (25-30 cm). Zone 3.
A. schoenoprasum (chives)
Of course, chives are best known as culinary herbs and are often relegated, for that reason, to the vegetable garden along with the other edible plants. However, with its beautiful pinkish purple umbels in late spring and attractive narrow upright foliage, it really should be placed on view in the flowerbed. It is very hardy and easy to grow, but can self-sow a bit enthusiastically. Clumping. 8 to 14 inches (20-35 cm). Zone 1.
A. cristophii (star of Persia)
This relatively short plant bears huge umbel up to 16 inches (40 cm) in diameter. The star-shaped pale purple flowers have a striking metallic sheen. It blooms in early summer. This allium tolerates partial shade better than many others. Bulb. 12-to 20 inches (30 to 50 cm). Zone 4.
A. x hollandicum ‘Purple Sensation’ (Purple Sensation allium)
Often sold as A. aflatunense ‘Purple Sensation’, this is the most popular of the “tall alliums,” especially because of the very reasonable price of its bulbs. It produces an erect stem bearing a sphere of bright purple flowers about 4 inches (9 cm) across. It makes an excellent cut and dried flower and is inexpensive enough to plant in swathes for a most dramatic effect. Like many tall alliums, its rosette of leaves begin to die back even as the plant blooms, so it is best placed towards the middle or back of the flowerbed so as to hide the yellowing leaves. Blooms in early summer. Bulb. 24-40 inches (60-100 cm). Zone 4
Allium ‘Gladiator’ (top left), Allium ‘Globemaster’ (top right), Allium ‘Mount Everest’ (bottom). Photos: Brent and Becky’s Bulbs, J.M. Van Berkel.
There are a variety of alliums similar to ‘Purple Sensation’, but with larger umbels and often taller stems that bloom more towards the middle of the summer. Among them are A. ‘Gladiator’, with a 6-inch (15-cm) umbel of sweet-scented lilac purple flowers, 4 feet (120 cm), zone 4, A. ‘Globemaster’, bearing an 8- to 10-inch (20-25 cm) globe of purple flowers, 30-38 inches (80-95 cm), zone 4 and A. ‘Mount Everest’, with a 5-inch (12 cm) ball of white flowers, 40 inches (100 cm), zone 4. ‘Globemaster’ is probably the best of the group, with its huge umbel and blooms that can last nearly a month, but it is a relatively newcomer and still very expensive. Bulb.
A. schubertii (tumbleweed allium)
This is more a curiosity than a highly ornamental plant. It bears a huge umbel about 16 inches (40 cm) across bearing ever-so-tiny purple flowers on stalks of varying lengths, like a constellation of mini-stars, giving its bloom a very airy and, quite frankly, bizarre effect. In nature, after the seed cases mature, the umbel breaks free and, pushed by the wind, rolls away as a tumbleweed, dropping seeds here and there, an innovative way to disperse them. It needs full sun and very well drained soil or it won’t be long-lived. Bulb. 12-24 inches (30-60 cm). Zone 5.
A. ‘Millenium’ (Millenium allium)
This recent introduction has quickly become the most popular of all the clump-forming alliums. Each tuft produces several to many 2-inch (5-cm) globes of rosy purple flowers over hordes of strap-shaped leaves. Mid-summer to late summer. Clumping. 15-20 inches (40-50 cm). Zone 4.
A. ‘Summer Beauty’ is similar to ‘Millenium’, but with pink flowers. It is sterile, so won’t self-sow. 15-20 inches (40-50 cm). Zone 3.
A. tuberosum (garlic chives)
This allium is both ornamental and edible. Its delightfully perfumed white flowers appear in tight domes in early fall. Its narrow, flattened leaves have a garlicly flavor and are used in cooking. Warning: this species tends to spread abundantly by self-sowing: make sure you mulch to keep it under control! Clumping. 15-24 inches (40-60 cm). Zone 3.
A. thunbergii ‘Ozawa’ (Japanese allium)
This is dwarf allium with short, erect, grasslike leaves. It bears globes of tiny reddish purple pendant flowers. This is one of the latest alliums to bloom, in October or November. Warning: it blooms so late in the season that, in cold climates, it doesn’t always have time to bloom before heavy frost, so the buds may be killed before ever opening. Clumping. 8-12 inches (20-30 cm). Zone 4.
Of course, there are many more alliums you can try. Give them a shot this summer during the “Year of the Allium”!