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08 Jan 2024

How to grow alliums and best varieties

Alliums (ornamental onions) are the star of the border in late spring. Discover our best allium varieties and tips on how to grow them

Ceri ThomasEditor, Which? Gardening

In this article

Key facts
How to grow alliums: month by month
Best allium varieties
Caring for your plants

Often the star of the gardens at the RHS Chelsea Flower Show, alliums (ornamental onions) with their purple globes are a stunning sign of summer's imminent arrival. Bees adore them, too.

There has been lots of breeding in alliums over the years, so there's a surprising number of varieties available, and not all of them bear the purple globe flower heads we're all familiar with.

Which? Gardening magazine grew a range of popular varieties to see which would give us the best display.

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Key facts

Plant type Summer-flowering bulb

Position Full sun

Soil Free-draining

How to grow alliums: month by month

January	February	March	April	May	June
			Flowering	Flowering	Flowering
July	August	September	October	November	December
Flowering		Plant	Plant

Best allium varieties

Which members can log in now to see the full results and which are our Best Buy varieties. If you're not a member, join Which? to get instant access.

Full testing results for alliums

Variety name	Overall rating	Height & spread (cm)	Flower impact	Flowering duration	Foliage impact (dieback)	Plant shape - steam strength	Bee/insect attraction	Pests & diseases
'Ambassador'
'Beau Regard'
A. cristophii
'Eros'
'Forelock'
'Gladiator'
'Globemaster'

_{Overall rating - the more stars the better. Rating ignores price and is based on: flower impact 35%; duration of flowering 20%; shape 15%; foliage impact 10%; bee/insect attraction 10%; pests and diseases 10%.}

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Caring for your plants

Planting

Plant bulbs at three times their own depth in the soil in autumn, spacing them about 20cm apart (or 10cm apart in the case of smaller bulbs, such as ‘Eros’).

Some alliums have rhizomes (underground stems) instead of bulbs; these look more like spring onions than dry bulbs on arrival. Plant these in autumn just below the soil surface and 10cm apart.

Alliums aren’t too fussy, but a sheltered spot with well-drained soil in full sun is ideal. You can also grow them in pots filled with a Best Buy compost for containers as long as you plant them at the necessary depth.

Record where you've planted your bulbs with Best Buy plastic-free labels

Cutting back

To keep alliums tidy, gather up the dead leaves in early summer and remove any stems that become detached at their bases in late summer.

Learn how to make compost

Supporting stems

Although most of the stems stood up reasonably well in our trial, in a very exposed site you might need to provide support for them.

Common growing problems

Alliums are generally trouble-free in borders, but watch out for the orange spots of rust, and cut back diseased foliage. Pests to keep an eye out for include slugs, snails and allium leaf miner. Alliums are hardy in the UK and can be left in the ground all year.