Purple alliums blooming

How to grow alliums

All you need to know about growing alliums, or ornamental onions, in this Grow Guide.

A table displaying which months are best to sow, plant and harvest.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Plant
Plant

Do not Plant in January

Do not Plant in February

Do not Plant in March

Do not Plant in April

Do not Plant in May

Do not Plant in June

Do not Plant in July

Do not Plant in August

Do not Plant in September

Do Plant in October

Do Plant in November

Do not Plant in December

Flowers
Flowers

Plant does not flower in January

Plant does not flower in February

Plant does not flower in March

Plant does not flower in April

Plant does flower in May

Plant does flower in June

Plant does not flower in July

Plant does not flower in August

Plant does not flower in September

Plant does not flower in October

Plant does not flower in November

Plant does not flower in December

Cut back
Cut back

Do not Cut back in January

Do not Cut back in February

Do not Cut back in March

Do not Cut back in April

Do not Cut back in May

Do Cut back in June

Do Cut back in July

Do not Cut back in August

Do not Cut back in September

Do not Cut back in October

Do not Cut back in November

Do not Cut back in December

Alliums are long-lived bulbous perennials, flowering for several weeks from spring to early summer. Loved by bees, they 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.

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How to grow alliums

Grow alliums in moist but well-drained soil in full sun. 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 bloomig and consider leaving the flowerheads in place as they look attractive in their own right, particularly in winter. Mulch annually with well-rotted compost or manure.

More on growing alliums:


Where to plant alliums

How to grow alliums - allium blooms against a blue sky
How to grow alliums – allium blooms against a blue sky

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.

For a dramatic display, grow alliums in large drifts through the border or naturalise them in your lawn.


How to plant alliums

How to grow alliums - planting an allium bulb
How to grow alliums – planting an allium bulb

Plant allium bulbs in autumn, at least four times the depth of the size of bulb. It’s better to plant them too deeply than too shallow.

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:


How to care for alliums

How to grow alliums - allium seedheads
How to grow alliums – allium seedheads

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.

Alliums 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: problem solving

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.

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:


Allium varieties to grow

Small green and pink flowerheads of Allium sphaerocephalon
Small green and pink flowerheads of Allium sphaerocephalon
  • Allium ‘Mount Everest’ – white, globe-shaped flowers held on 90cm stems. The May/June flowers are 10cm across
  • Allium sphaerocephalon – smaller flower heads in June or July that start green and turn a deep pink. Reaches a height of 60cm but does tend to romantically fall about
  • Allium cristophii – offers impressive flowers that are 20cm across held on stems of 20cm in June. The purple head of flowers is quite open unlike the tightly packed ‘Purple Sensation’. Dramatic silvery foliage
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  • Allium moly – small but very bright yellow flowers that can thrive on a woodland edge. Flowering in May or June on 30cm stems