There are well over 500 different Allium species, although gardeners grow only a few of these. Alliums combine wonderfully with old roses, with silver leaved plants and with the lime-green tones of Alchemilla mollis. Still, species with perfectly round flower heads make also a great element in contemporary garden designs.
Ramson, rampion (A. ursinum) is not only the most shade-tolerant but also the most rampant allium described in this article. While care should be exercised in introducing it into some gardens, it is perfect for difficult, shaded places where little else will grow. In spring, pretty white flowers atop 12-18" (30-45 cm) stalks pop up among the dark green foliage, which resembles that of a miniature hosta.
The succession continues with Turkestan onion (A. karataviense) from central Asia, and in June the early summer species are at their best. A great plant for the front of the border, the Turkestan onion features plump, dark green foliage that forms ground-hugging arches. In the midst of the unusually shaped leaves, eye-catching balls of pinkish white flowers appear in May. The blossoms last for up to three weeks and then leave a handsome seed head before fading away. Plants vary in height from 6-10"(15-25 cm) and do well in partial shade where they receive four hours of direct sun.
A. cristophii (syn. A. albopilosum) has large heads of shining purple stars on quite short stalks. A. cristophii flowers in early summer, timing their appearance perfectly to coincide with the old roses that they complement so beautifully. A. cristophii is one of the largest allium flowers, at some 8" (20 cm) across made of larger, almost spiky starflowers. Coming from the rocky hillsides of Turkey and into central Asia, a well-drained, warm site is essential.
A. hollandicum (syn. A. aflatunese) is a robust plant with smaller, deep lilac with a tighter mass of flowers; the flower head is about 4" (10 cm) across. Growing to 2-4 ft (70 cm to 1 m) it is a good plant for the middle of the border and associates particularly well with roses and herbaceous plants. The form, A. hollandicum 'Purple Sensation' is a deep, magenta-purple and very covetable. A. hollandicum will happily self seed, so take care that you dead-head if you do not want volunteers in your borders.
A. giganteum is, as its name suggests, very tall, growing to 4ft (1.5 m). It needs a sheltered position protected from strong winds. The flowerheads are pale lilac in a tightly packed, round globe, and white forms are available. Coming from Central Asia it likes a fertile and moist, but well drained, soil and can be propagated from seed when ripe or offsets taken in the autumn. If frosts threatened in spring protect the new foliage as they can easily be damaged.
By early July the small herbaceous species are beginning to flower. Both the bright blue A. cyaneum from the high mountains of western China, and the purplish A. cyathophorum var farreri are good in rock gardens or in special places which are moist in summer; they need the same conditions as garden chives.
A group of particularly drought-resistant species are at their best in late June, July and August. Their bulbs grow through the winter and form leaves in spring; with the onset of summer the leaves die away, but the flower stem survives, to open its flowers in the dry season where there is less competition for pollinating bees. This group includes the bright blue A. caeruleum with a tight head and A. sphaerocephalum with slightly larger heads of deep purple. A little later the yellow A. flavum has small yellow flowers on thin stalks of different lengths and unusual grey leaves. Later-flowering still are the species A. paniculatum and A. carinatum subsp. pulchellum, with pinkish, purple or white flowers which last into September. In A. paniculatum the anthers are mostly inside the flower, in A. carinatum anthers and stamens stick out of the flower.
Lebanon onion (A. zebdanense) is covered with large, brilliant white flowers from late April to mid-May. An ideal plant for a dry, woodland shade setting filed with humus-rich soil, it grows between 12-16" (30-40 cm) in height. The Lebanon onion is especially beautiful when planted under shrubs that are late to leaf out or among hostas. Within two weeks after the last bloom fades, the plant goes completely dormant.
Although Nodding onion (A. cernuum) is native to rocky slopes and dry hillsides across a wide swath of North America, the easy-care charms of this extremely attractive flower are just beginning to be recognized. Shade gardeners particularly appreciate the nodding onion's ability to flower with as little as two hours of direct sun. The plant is quite adaptable, growing 12-24" (30-60 cm) high in exposed rocky beaches, cool mountain woods or dry, open woods. In bud form, the flowers resemble large white drops; the buds cascade open into a lacy spray of white, pink, rose or lilac flowers in midsummer.
Lavender globe lily (A. senescens, often sold as A. tanguticum) grows 18-30" (45-75 cm) tall and has dark green, straplike leaves. Round balls of lilac flowers appear in mid-to late summer. The clumps increase in size each year and mine have reached the point where they are large enough to produce a succession of bloom for six weeks.
Wild leek, ramp (A. tricoccum) native in cool, deciduous woods from New Brunswick to North Carolina and as far west as Iowa, this 8-10" (20-25 cm) high plant will bloom in heavy shade. Its leaves are considered an early spring taste treat. After the leaves wither and disappear, stalks topped with greenish white flowers appear in late June or cerly July.
Thunberg onion (A. thunbergii) The purple flowers on this 8-12" (20-30 cm) tall late bloomer don't even begin to open until late October.
Lastly, the 'Golden Allium' (A. moly) is a clump forming plant with bright golden heads of up to 30 flowers in summer. Only 6-10"(15-25 cm) tall, it is a great front of border plant but take care, as it can become invasive its many offsets quickly colonising in a suitable site. It enjoys a shady position and is especially useful in a woodland scheme with pulmonarias and pink fringed bleeding hearts.
You should plant in full sun in well drained areas. After the flower is finished blooming you can cut the flower stalk. Leave the leaves on the plant to help feed the bulb for next year. The allium requires little care once the plant is established.
When the leaves turn yellow, you can cut them down at ground level. The allium is a bulb. Each year smaller bulbs grow around the parent bulb. You can gently lift the plant out of the ground and remove the smaller bulbs if the plant becomes crowded. The smaller bulbs can be planted elsewhere or given to friends.
Even gardeners with tiny gardens can grow alliums in containers. Always use a reasonably deep container, especially for larger varieties. Plant at three times the depth of the bulb in well-drained compost (this also applies when planting in the open ground).
Although the container plants will need repotting into fresh compost every year, you don't need to do anything more, and they shouldn't require extra feeding as long as their foliage is left to die back naturally. This enables them to build up energy for the following year. Like some other bulbs, they're naturally long-lived and survive for years if left undisturbed.
If you want large drumstick alliums, note that its dying foliage can be disguised behind a few pots of bushy annuals or clipped box for a more formal look.