Bulb
How to grow alliums
Allium hollandicum, A. cristophii and others
Plant ornamental allium bulbs from September to November in full sun and free-draining soil, three to four times their own height deep, for flowers in May and June. Drainage decides whether they come back: on heavy clay, plant on a layer of grit or grow them in pots. The leaves yellow as the flowers open, so set the bulbs among perennials that cover the mess. Feeding matters very little.
- Hardiness
- Fully hardy
- Position
- Full sun
- Soil
- Free-draining
- Ideal pH
- 6.0 to 7.5
- Water
- Low
- Feeding
- Light feeder
Sowing and planting alliums
WhenPlant Sep to Nov; flowers May to Jun
Starting off
Plant dry bulbs Sep to Nov, 10 to 20 cm deep on a grit layer in heavy soil, nose up. Divide clumps and replant offsets in Sep every 3 to 4 years once flowering declines. Seed of A. cristophii sown fresh in Jul germinates in spring and flowers in 3 to 4 years; 'Purple Sensation' self-seeds in gravel.
Spacing and planting
Large types such as A. hollandicum 'Purple Sensation' 20 to 30 cm apart, A. cristophii 25 cm, small A. sphaerocephalon 10 cm; plant bulbs 3 to 4 times their height deep, in practice 10 to 20 cm. Large types fine in a 40 cm pot; small types in a 25 cm pot.
Varieties worth growing
- A. hollandicum 'Purple Sensation'
- The standard May allium: deep purple, about 90 cm, cheap enough to plant in drifts and the most reliable to return and seed about.
- A. cristophii
- Shorter at 50 to 60 cm with metallic lilac heads 20 cm across in June; the best seed heads for drying.
- A. 'Globemaster'
- Very large violet heads that last for weeks because the flowers are sterile and set no seed. Costs more per bulb, so use a few as accents.
- A. 'Mount Everest'
- Tall white allium at about 1.2 m, flowering a little after 'Purple Sensation'; good against a dark hedge.
- A. sphaerocephalon
- Small maroon drumsticks in July and August that extend the season by two months; inexpensive, thin-leaved and good threaded through grasses.
Alliums month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Nothing to do. Keep pots out of standing water.
- February
Shoots of the early kinds show. Clear wet leaf litter off them and watch for slugs.
- March
Leaves are up. A light potash feed on poor soil or old clumps; start a fortnightly liquid feed for pots.
- April
Flower buds rise and leaf tips begin to yellow, which is normal. Water pots in a dry spell.
- May
'Purple Sensation' flowers, then 'Mount Everest' and 'Globemaster'. Let the leaves die back; do not cut or tie them.
- June
A. cristophii flowers. Stop feeding pots as the flowers fade. Pull away dead leaves once they come free.
- July
A. sphaerocephalon flowers. Cut off heads you do not want seeding, or leave them for structure. Sow fresh A. cristophii seed.
- August
Cut seed heads for drying. Order bulbs while the choice is good.
- September
Start planting. Lift and split congested clumps and replant the largest bulbs.
- October
Main planting month: three to four times the bulb's height deep, on grit in heavy soil.
- November
Finish planting. Raise pots on feet for the winter.
- December
Nothing to do.
Feeding alliums
A light feeder. In ordinary garden soil ornamental alliums need no fertiliser at all; sun and drainage do the work. Feed only pots, poor sandy soil, or clumps that have flowered less each year.
Low, sun and sharp drainage matter more than feeding.
Feeding plan
Planting, September to November
Grit, no fertiliser
Nothing in the planting hole. On heavy soil put a 3 to 5 cm layer of sharp grit under each bulb or group.
March as leaves emerge, poor soil or tired clumps only
20 g/m², the bottom of the label range, scattered round the clump once and watered in. A group of five large bulbs covers about a quarter of a square metre, so 5 g.
March until the flowers fade, pots only
3 ml per litre of water (30 ml in a 10 litre can), once a fortnight. The label allows more often; alliums do not need it.
After flowering
Nothing
No feed once the leaves have died back. The bulb is dormant and cannot use it.
Signs to watch
Leaves but no flowers in year three
Bulb split into offsets too small to flower
Lift in Sep, replant the largest 15 cm deep, high-potash feed in Mar
Leaf tips yellow early in Apr
Normal die-back, not nutrition
Hide with perennials
Soft, rotten bulbs
Waterlogging
Raise the bed with grit
Pests, diseases and problems
Leaves yellow and wilt in spring; bulb pulls up easily with white fluffy mould and tiny black dots at the base
Onion white rot, a soil fungus that also attacks onions, garlic and leeks and persists in soil for many years
There is no cure. Dig out affected bulbs with the soil around them and bin them, do not compost. Do not replant any allium, edible or ornamental, in that spot; grow them in pots of fresh compost instead.
Young leaves ragged and holed in March and April; flower buds chewed
Slugs and snails
Hand-pick after dark, keep mulch and debris away from emerging shoots, and use nematodes once the soil is above 5 °C. Leaf damage is mostly cosmetic because the leaves die back at flowering anyway.
Pale oval patches on the leaves that turn grey-purple and furry in damp weather, then collapse
Onion downy mildew, worst in cool, wet springs and crowded plantings
Remove affected leaves promptly, space bulbs so air moves between them, and keep ornamental alliums away from the onion bed.
Tall stems lean towards the light or fall over at flowering
Too much shade, or soft growth in rich, moist soil
Move the bulbs in September to a spot with sun for most of the day and do not feed. Planting at full depth, 15 to 20 cm for large bulbs, also anchors the stem.
Grass-like seedlings carpeting the bed in spring
Self-seeding, mainly from 'Purple Sensation' and A. cristophii
Cut the heads off before the seed capsules split in July, or hoe the seedlings while small. Sterile hybrids such as 'Globemaster' do not seed.
Pruning
Pruning and care
Leave seed heads for structure through summer and cut in Aug or Sep, or deadhead to stop 'Purple Sensation' seeding everywhere. Leave the yellowing foliage, which dies as flowers open, until it pulls away. No staking; lift and divide in Sep every 3 to 4 years only if crowded. Fully hardy, no protection.
Good to knowPlant in autumn; leave seed heads for structure. Foliage dies as it flowers, hide it among perennials.
Growing alliums in pots
Alliums suit pots well and it is the answer on heavy clay. Use a pot at least 40 cm wide and deep for large kinds, 25 cm for A. sphaerocephalon, filled with loam-based compost mixed with about a quarter grit. Plant at the same depth as in the ground and closer together, 10 to 15 cm apart for big bulbs, so the display is full. Stand the pot on feet over winter because cold wet compost rots the bulbs faster than frost harms them. Water from March until the leaves yellow, then let the pot dry. Bulbs flower well for one or two years in a pot; after that, plant them out in September and start again with fresh ones.
Alliums: common questions
Do alliums come back every year?
Yes, in sun and well-drained soil most ornamental alliums are perennial and flower for many years. 'Purple Sensation', A. cristophii and A. sphaerocephalon are the most reliable. The largest hybrids can fade after two or three years on heavy or wet ground, where the bulbs rot or split into small offsets that need lifting and replanting.
Can I plant allium bulbs in spring?
No, dry bulbs planted in spring rarely flower, because they need a winter in the ground to root and to be chilled. Bulbs you forgot can still go in as late as December if they are firm and the soil is not frozen or waterlogged. In spring, buy alliums already growing in pots and plant those.
Do alliums spread?
Some do, by seed and by offsets. 'Purple Sensation' and A. cristophii seed freely into gravel and bare soil, and seedlings take three to four years to flower. Cut the heads before the seed drops if you do not want them. Sterile hybrids such as 'Globemaster' stay where you put them and only bulk up slowly.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.