Alliums

Alliums in flower

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 tollerant.

Family: Alliaceae (onion)
Botanical Name: Allium
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.

Habit: Columnar/Upright.

Type: Bulbous herbaceous perennials.

Hardiness: Hardy in all of the UK (down to -20°C)

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 variety. Also good for deep pots and containers. The leaves can start to brown and dieback once in flower, so it is best to mask them with other forground 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 good balanced fertiliser in the spring. Lift and divide established clumps once the leaves and flowers have died back natually.

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.

Pruning Alliums

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 architecural affect if required.

Pests and Diseases

Emerging shoots are susseptible to slug damage. Can be affected by onion white rot, onion fly or downy mildew.

Propagating Alliums

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.

Popular Varieties of Allium Grown in the UK

Allium species include:

A. aflatunense has rich lilac or white flowers in late spring. Height to 3ft (90cm). Suitable for drying.

A. cernuum (lady's leek) produces pink to red- purple, bell-shaped flowers in summer. Height from 8-18in (20-45cm).

A. christophii (star of persia) has bright, blue-purple starry metallic flowers with heads up to 10in (25cm) across in early summer. Heigh 12-20in (30-50cm). Good for cutting and drying. Available at You Garden.

A. cyaneum (dark blue garlic) has densely tufted, grass-like leaves with deep-blue open flowers in summer. Height and spread about 6in (15cm). Good for rock gardens.

A. moly (lily leek) is a low growing form with tulip-like leaves and bright yellow, star-shaped flowers from early to mid summer. Available at Thompson and Morgan.

A. giganteum (giant onion) has grey/green strap-like leaves and starry, metallic-lilac, summer flowers, in spherical clusters 6in (15cm) wide. Height to 4ft 1.2m).

A. karataviense is a dwarf form ideal for 'the rock garden. Height to 8in (20cm). Green white and purple flash flowers. Handsome foliage.

A. narcissiflorum has greyish-green grassy leaves with rose-purple, bell-shaped flowers carried in small pendant clusters in early summer. Height and spread from 8-12in (20-30cm). Good rock-garden plant.

A. nigrum has globe-shaped flowers above broad deep-green leaves. Available at You Garden.

A. ramosum (fragrant-flowered Garlic or Chinese chives) has silvery-white, starry flowers, on upright stems from May to July. Height to 18in (45cm), spread 4in (10cm). Available at Thompson and Morgan.

A. schoenoprasum (chives) is a popular herb with a mild onion flavour.

A. siculum (Sicilian honey garlic) produces flowers in May and June with hanging bell shaped flowers that are greenish white and tinted with red. Height to 4 ft.

Allium Hybrids include:

A. 'Gladiator' has large (up to 6") spherical blooms of starry purple with delicate silvery tips. Height to 4ft (120cm). Available at Thompson and Morgan.

A. 'Globemaster' produces magnificent spherical lilac-purple blooms, up to 6in (15cm) across. Height to 30in (80cm). Available at Thompson and Morgan.

Allium 'Mars' produces large magenta-pink flower spheres on long stems above broad, green leaves. Height to 3ft (90cm). Available at You Garden.

A. 'Millenium' produces rounded heads of light purple, star-shaped flowers on upright stems. Height to 2ft (60cm). Available at Thompson and Morgan.

A. 'Purple Sensation' has spectacular lilac-purple flowers up to 6in (15cm) across. Height to 3ft (90cm). Available at Thompson and Morgan and You Garden.

A. stipitatum 'Mount Everest' produces globes of more than 50 star-shaped blooms in early summer. Available at Thompson and Morgan and You Garden.