Bulb
Ornamental onion
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Flowers | Flowers in May | Flowers in June | ||||||||||
| Plant | Plant in September | Plant in October | Plant in November | |||||||||
| Looks good | Looks good in May | Looks good in June | Looks good in July | Looks good in August |
Overview
Alliums fill the gap between tulips and roses with tall stems topped by spheres of tiny starry flowers. 'Purple Sensation' is the classic and comes back reliably; 'Globemaster' produces huge violet heads; Allium sphaerocephalon, the drumstick allium, flowers later in July with egg-shaped claret heads; and Allium cristophii has metallic lilac globes that dry beautifully. Bees and hoverflies swarm over them.
Where to grow ornamental onion
Full sun and soil that does not stay wet in winter are the two essentials. Because the strap-shaped leaves yellow just as the flowers open, slot bulbs among plants that fill out in early summer, such as catmint, hardy geraniums or salvias, which hide the untidy foliage.
Planting
Plant from September to November, about three times the bulb's height deep; for large varieties that means 15cm or more. Place them in loose groups through a border so the heads appear to float above other plants.
Care through the year
Spring
Watch for slugs on emerging leaves. Stake giant types in exposed gardens.
Summer
Leave faded heads to form seed heads, which stay decorative for weeks, or cut them for dried arrangements.
Autumn
Plant new bulbs and pull out collapsed stems. Add grit to heavy soil before planting.
Winter
Bulbs are dormant. Avoid treading on beds where they are planted.
Pruning
No pruning is needed. Remove dead stems once the seed heads have lost their looks.
Propagation
Established clumps form offsets that can be lifted and separated in late summer once the foliage has gone. Many alliums self-seed, though seedlings take a few years to reach flowering size.
Common problems
Allium leaf miner, a fly whose larvae tunnel into leaves and bulbs, has spread across much of the UK; cover with insect-proof mesh during its spring and autumn flights if it is a problem. Onion white rot can affect bulbs in infected soil. Slugs damage young shoots.
Guides to the problems most likely to affect ornamental onion:
Something else wrong? Diagnose it by symptom.
Month-by-month reminders
Jobs for this plant come round in September, October and November. Each month page lists everything else worth doing in the garden at the same time.
Related plants
Sources
Botanical names follow Kew's Plants of the World Online; growing attributes were checked against the references below. Text is our own. See our editorial policy.