You may have seen them in flower beds and landscaping: large globes of star-shaped flowers, usually purple, carried on sturdy upright stems. These are ornamental alliums, also known as ornamental garlic or ornamental onions, as they are very closely related to real garlic and onions. They begin to bloom in late May/early July, flowering for two to three weeks. But don’t rush to the garden center, as large alliums won’t be available until fall.
Among the Last Bulbs to Bloom
Even though they bloom in early summer, alliums are sold as “fall bulbs”: the bulbs arrive in stores in mid-September. So, make a note in your fall calendar to “buy allium bulbs” if you want to enjoy their beautiful flowers next spring.
These curious plants produce a large, flattened rosette of broad, pointed leaves in spring, but flowering does not begin until early summer, just as the foliage begins to turn yellow. They should therefore be placed in the background, where their beautiful flowers will be easily visible, but not their yellowing leaves. Each rosette produces a single flower stalk topped with a huge sphere of star-shaped flowers. Over the years, the bulb divides, forming several rosettes and as many flower stalks. The basic color of the flowers is shades of purple—from purple to lilac, depending on the variety—often with a metallic sheen. There are also a few cultivars with white flowers.
But the effect doesn’t end after flowering, as the flower stems and flowers dry in place, creating a geodesic dome effect that will last until fall. And you can also harvest the dried stems as decoration for your home.
Cultivation
Plant large alliums in autumn, between September and November, in full sun in any well-drained soil, rich or poor. Plant the bulb with the tip pointing upwards and the flattened part, sometimes with dried roots, pointing downwards, at a depth of 10 to 20 cm (4 to 8 inches). Space the bulbs 20 to 25 cm (8 to 10 inches) apart and water to finish planting.
Alliums are essentially maintenance-free once established, unless you wish to cut back the dried leaves and stems. They are hardy, with most varieties growing easily in zone 4.
Varieties
There is a wide selection of large alliums, but relatively few of them make it into our stores. The most popular is Allium hollandicum ‘Purple Sensation’ (60-100 cm, 2-3 feet), sold under the name A. aflatunense ‘Purple Sensation’. Its popularity is largely due to its very low price. It is the classic garden allium. ‘Lucille Ball’, ‘Gladiator’ and ‘His Excellency’ are similar, but come in various other shades of purple. A. ‘Mont Blanc’ has white flowers. The giant allium (A. giganteum), 80-150 cm (3-5ft), is often offered but is not a good choice: it does not live long in our climate, which is too humid for its liking. If the soil is very well-drained, it can live longer, but it is often more capricious than other species.
Crowned perennial of the year in 2018, Allium ‘Millenium’ has quickly established itself as a must-have thanks to its abundant summer flowering, edible foliage, and high resistance. Unlike bulbous alliums, it forms a dense clump of dark green leaves topped with pinkish-purple flower balls that attract pollinators and repel herbivores. Its flowering, which lasts about four weeks in July or August, is one of the latest and longest lasting among alliums. Hardy to zone 4 (and sometimes zone 3), it tolerates drought, does not become invasive, and is easily propagated by division. A must-try for extending the allium season!
The ultimate large allium, however, is A. ‘Globemaster’ (80–95 cm, 3 feet). Its gigantic globe, measuring 20–25 cm (8-10 inches) in diameter, produces flowers that can last for five weeks! But ‘Globemaster’ is expensive. Many would say, however, that it is well worth the price!
Order Now for Fall
If you want to order your allium bulbs now rather than wait until fall, you can do so by catalog. This way, you can be sure to get the variety you want. Some garden centers also offer potted alliums in the spring or early summer, especially perennial varieties such as Allium ‘Millenium’. These plants can be replanted in the garden after flowering. However, large bulbous alliums are less commonly available in pots, are often more expensive, and the bulbs must be replanted quickly to ensure their survival.
Larry Hodgson has published thousands of articles and 65 books in French and English over the course of his career. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This text was originally published in Le Soleil on June 26, 2011.