How to grow alliums
All you need to know about growing alliums, or ornamental onions, in our Grow Guide.
Alliums are bulbous perennials, living up to four years after planting. With a long flowering season, they bloom for weeks on end, bridging the gap between spring and summer. Loved by bees, alliums bear beautiful pompom flowers in shades of purple pink and white, and look fantastic when planted in large groups. Alliums make excellent cut flowers, both in fresh and dried flower arrangements.
How to grow alliums
Grow alliums in moist but well-drained soil in full sun. Plant as many as you can afford to buy – the most impressive allium displays arise from mass plantings. It’s a good idea to grow them among low-growing herbaceous plants, which hide their unsightly strappy foliage after flowering. Let allium foliage die down naturally after blooming and consider leaving the flower heads in place as they look attractive in their own right, particularly in winter. Mulch annually with well-rotted compost or manure.
Alliums: jump links
- Choosing alliums
- Planting alliums
- Caring for alliums
- Allium pests and problems
- Where to buy alliums
- Alliums to grow
When choosing alliums to grow, think about your garden space. Will you be growing in drifts through the border or planting in bulk, in pots? As part of a prairie planting scheme or something more formal? It's also important to think about the colour of your alliums – most allium flowers are purple but some come in shades of blue, white, yellow and pink. Also consider the size of your allium – that's the flower size as well as the overall height of the plant. Flower sizes range from just a few centimetres to over 20cm (8in) in diameter, while the eight of alliums can vary significantly, too.
Large, tall alliums such as 'Purple Rain' and 'Globemaster' work well when planted individually or in drifts. Shorter varieties such as Allium christophii work well in pots. Drumstick alliums such as Allium sphaerocephalon look great in prairie planting schemes.
Where to plant alliums
Alliums do best in a sunny spot in a very well-drained soil. They’re not fussy about soil type. Plant taller varieties towards the back of a border and shorter-growing types in the front. Alliums are well suited to growing in pots but their strappy foliage can look unsightly after flowering.
Alliums produce foliage before the flowers appear. This often means they're better suited to the middle of a border where the faded foliage will go unnoticed while the flowers put on a show. To avoid seeing the faded foliage, plant alliums in amongst ornamental grasses and perennials.
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For a dramatic display, grow alliums in large drifts through the border or naturalise them in your lawn.
How to plant allium bulbs
Plant allium bulbs at least four times the depth of the size of bulb (at least 15cm deep). It's better to plant them too deeply than too shallow. It's best to not plant more than one allium bulb in the same planting hole, but if you want a more naturalistic display you can plant smaller growing alliums 7-10cm apart, and taller species around 20cm apart.
If the soil is moist there's no need to water them in. In spring, when growth starts to appear, apply a balanced fertiliser to poor soils.
Watch our No Fuss video guide with Rosie Yeomans, to learn how to layer allium bulbs with others in a pot:
When to plant allium bulbs
The best time to plant allium bulbs in the UK is in autumn, typically from September to November. If you don't plant your allium bulbs by the end of November don't worry – you should be able to plant them up to the end of December without any problems, just make sure the bulbs are still firm and show no signs of mould or disease before planting (discard any that do). You may find that a late planting means your alliums will flower later than usual in their first year, but will catch up the second year.
How to care for alliums
Taller types may require support in exposed positions. Once the flowers have faded leave them on the plant until they fall apart as they offer fantastic winter interest. Some gardeners pick the seedheads and dry them in order to use them as a decoration in the house.
Allium bulbs can be left in the garden year after year. Try to remember where you’ve planted bulbs so you don’t damage them when planting new plants.
How to propagate alliums
After a few years allium bulbs will multiply. In some cases you'll notice the white bulbs being pushed out of the soil. In late autumn or very early spring carefully lift the bulbs and gently peel off the offsets to replant straight into the soil.
To grow allium from seed leave the flowerheads on the plant and collect the ripe seed and sow it straight away. bear in mind that growing alliums from seed is a long process, as it will be years before you achieve a flowering plant.
Growing alliums: pests and problem solving
Allium white rot is a fungal disease, which inhibits the growth of onions and other alliums. To prevent recurrent infections, clear and burn the affected plant material and avoid planting alliums in the same position for at least five years.
Alliums can out-grow their space. Find out how to reduce the number of alliums growing in a border, in this video clip from Gardeners' World:
Advice on buying alliums
- Carefully sesearch the height and spread of your alliums before buying them, so they will fit well into your garden design
- Choose firm bulbs with no sign of mould, and plant them at theor freshest, ideally within a week of buying
Where to buy alliums online
20 alliums to grow
The drumstick allium, Allium sphaerocephalon, is a striking allium, bearing dense green drumstick-style flower heads which mature to maroon-red. It’s a great choice for growing in a mixed herbaceous border among ornamental grasses, or gravel gardens. It also works well in pots.
H x S: 90cm x 8cm
Allium cristophii produces striking globes of violet, star-shaped flowers in early summer. The long, linear leaves die back before the blooms appear in early summer.
H x S: 60cm x 20cm
Allium ‘Millennium’ is a fantastic mid- late-summer-flowering allium, bearing large, rounded heads of pink-purple flowers in June and July. It’s perfect for growing in a mixed herbaceous border and is best planted in large groups.
H x S: 40cm x 45cm
Allium cernuum is a clump-forming allium, bearing open clusters of pink, nodding flowers with protruding yellow stamens. It’s an extremely attractive variety and is easy to grow. It’s perfect for growing in a mixed herbaceous border or in drifts as part of a prairie scheme.
H x S: 50cm x 10cm
- Buy allium cernuum from Sarah Raven
Allium ‘Globemaster’ bears rounded, deep violet flower heads, 15-20cm in diameter, from late spring to early summer. It works well when planted in drifts with ornamental grasses and other alliums, including lighter flowered ‘Beau Regard’.
H x S: 1m x 50cm
Hailing from Afghanistan and Tadjikistan, Allium nevskianum is a low-growing and rarely grown allium, bearing large, deep red globular flower heads above attractive, large blue-grey leaves. Grow it at the front of the border or make a feature of several planted together in a pot.
H x S: 30cm x 20cm
Allium 'Mont Blanc'
Allium ‘Mont Blanc’ bears dense, spherical flower heads of white, star-shaped flowers on tall, upright stems in late-spring and early summer. It’s a great choice for sunny borders and gravel gardens, where it can be planted in clumps, or drifts among ornamental grasses and other alliums. It makes a wonderful cut flower.
H x S: 1.1m x 20cm
Allium schubertii is an unusual-looking allium, bearing spiky heads of flowers with stems of different lengths, resulting in a dramatic effect. Individual florets are purple with a green centre. It’s perfect for growing in sunny borders and in pots as an unusual centrepiece, and it makes a striking cut flower.
H x S: 50cm x 25cm
This allium bears clusters of long-lasting, pink, bell-shaped flower heads over strappy foliage. Allium unifolium makes a great addition to alpine beds or at the front of a sunny border.
H x S: 30 cm x 10cm
Allium 'Mars' bears well-formed, dark-red-purple, compact flower heads in late-spring and early summer. It's is a fantastic choice for sunny borders, and works well when planted in drifts with ornamental grasses and other alliums.
H x S: 1.1m x 30cm
Allium 'Purple Sensation'
The tall flowers of Allium 'Purple Sensation' appear in summer, showing off rounded heads full of deep violet flowers. It's best to remove the immature seed-heads as the seedlings tend to have paler flowers.
H x S: 80cm x 30cm
Allium 'Purple Caila'
Allium 'Purple Caila' bears large flower heads of purple, star-shaped florets on tall, bare stems in late spring to early summer.
H x S: 20cm x 30cm
Allium 'Red Mohican'
Allium 'Red Mohican' is a striking allium, bearing unusual, maroon-red drumstick-style flower heads with extra tufts at the top, tipped with tiny white flowers (resembling a mohican).
H x S: 90cm x 20cm
This compact allium with bright pink to purple flowers makes a great addition to sunny borders or alpine beds.
H x S: 10cm x 10cm
Allium 'Purple Rain'
Allium 'Purple Rain' is a cross between Allium 'Purple Sensation' and Allium Cristophii. It bears huge purple, globe-shaped flower heads measuring up to 15cm in diameter.
H x S: 90cm x 30cm
Allium caeruleum is an unusual blue-flowered allium. It bears small, dense globes of star-shaped flowers on sturdy stems.
H x S: 60cm x 25cm
Allium 'Dready' is a cultivar of Allium vineale, as is related cultivar 'Hair'. 'Dready' refers to the masses of dreadlock-like curling tendrils in green-red, which grow out from mauve drumstick flower heads.
H x S: 40cm x 10cm
Native to California and southern Oregon, Allium falcifolium is a relatively rare, low-growing alpine allium, bearing deep pink-purple shaggy flowers in late summer.
H x S: 20cm x 10cm
This is a striking allium with dark purple, half round, shaggy flowerheads on tall stems. Allium 'Miami' makes a great addition to a sunny summer border, working particularly well planted in drifts with ornamental grasses and other alliums.
H x S: 90cm x 20cm
With cream-white semi-globular white flowerheads, over tall, sturdy stems, Allium nigrum makes a striking addition for your sunny borders in late spring to early summer.
H x S: 75cm x 30cm