A large group of bulbous plants that include onions, garlic, leaks, and hardy ornamental perennials. The ornamental forms are best for the flower garden. Alliums like hot dry conditions and are mostly drought tolerant.
Family: Alliaceae (onion)
Botanical Name: Alliums
Common Names: Ornamental onion
Foliage: Strap-shaped, grey-green leaves. Deciduous (dies back after flowering). Strong onion or garlic scent.
Flowers: Most forms have tall to medium height stems topped with spherical flower heads of starry flowers (umbels). Heads are small to large, in shades of white, pink, violet, or purple (depending on variety).
Flowering Period: Spring to mid-summer.
Soil: Moist but well-drained soil (chalk, clay, sand, or loam). Prefers chalky ground but will do well enough in most other well-drained garden soils. Dislikes exposed or waterlogged sites.
Conditions: Full sun. Can be planted in any aspect so long as it is a sheltered spot.
Type: Bulbous herbaceous perennials.
Planting and Growing Alliums
Alliums are easy to grow, so long as the soil conditions are appropriate. The ground must be moist but well-drained, so improve heavy clays with horticultural grit or sand and enrich light, chalky or sandy soils with organic matter.
Good for the front or back of the border, depending on the variety. Also good for deep pots and containers. The leaves can start to brown and die back once in flower, so it is best to mask them with other foreground plants
Good for the front or back of the border, depending on the variety. Also good for deep pots and containers. The leaves can start to brown and die back once in flower, so it is best to mask them with other foreground plants.
Plant out dormant bulbs in early autumn, in any good garden soil provided it is well-drained and in an open sunny location. Plant deeply, at least four times the diameter of the bulb. Once established they can be left undisturbed for many years.
Most tall forms are good as cut flowers and also good for drying. To dry, pick the flowers as soon as they are fully open. Hang the stems upside down, singly, in a cool airy place. Leave them undisturbed until they have completely dried.
Taking Care of Alliums
Mulch and apply a well-balanced fertilizer in the spring. Lift and divide established clumps once the leaves and flowers have died back naturally.
Poor flowering can result from planting to shallow, growing in wet soils or very very dry soils or from cutting down leaves before they have died back naturally. They may also flower poorly if too much shade is given from other plants.
No pruning required. Cut stems down to ground level once flowers and leaves have died back naturally. The seedheads can also be left on over-winter for architectural effect if required.
Pests and Diseases
Emerging shoots are susceptible to slug damage. Can be plagued by onion white rot, onion fly, or mildew.
Sow seed in containers in the spring (Note: most hybrids forms will not come true from self-sown seeds). It can take several years for the bulbs to reach flowering size.
Alternatively, lift the bulbs in the autumn, detach the small offsets and grow these on to maturity.