Allium oreophilum

Allium giganteum

Height: 20-150cm (8-60in)

Planting distance: 5-30cm (2-12in)

Features: flowers summer

Soil: well-drained

Site: open, sun

Type: bulb

Ornamental onions are becoming increasingly popular because of their easy-going nature, tough constitution and long-lasting flowers. These heatand sun-loving bulbs flower in summer and, according to variety, range from white, yellow and blue to deep lilac and rose.

Some alliums are ideal for mixed or herbaceous borders, others for rock gardens and sink gardens. Some are excellent for drying for cut-flower displays.

Their onion-like smell is only noticeable when leaves and stems are bruised, or if fresh alliums are used in flower arrangements, in which case a few drops of bleach added to the water prevent the odour forming.

Popular species

Allium beesianum has pendent heads of blue flowers in late summer and narrow, grey-green leaves. It grows 20-30cm (8-12in) high; plant 5-10cm (2-4in) apart.

Cultivation

Plant outdoors in mid spring, setting the crowns about 10cm (4in) below ground level in soil enriched with well-rotted garden compost or manure. Do not disturb them after planting or they won’t flower.

Water well in dry weather. After flowering, cut the stems back to ground level. In cold areas protect the roots against frost: apply a winter mulch to plants in a bed or large tub, and bring those in small containers into a cool but frost-free place.

Propagation: When clumps become overcrowded, divide and replant the fleshy roots in mid to late spring, ensuring each piece has a crown.

Pests and diseases: Trouble free.

Allium allium, ornamental onion is 5cm (2in) high, plant it 15cm (6in) deep.

Apply a spring dressing of general fertilizer or bonemeal. After flowering, cut off the heads – some make good dried flower arrangements. In autumn, remove the dead leaves and flower stalks.

You may need to stake tall alliums growing in a windy position.

Propagation: Detach bulbils from the base of mature bulbs in autumn or spring when the new growth appears. Replant them immediately and keep the soil moist.

Pests and diseases: Young shoots, leaves and stems are attractive to slugs. White rot can cause the leaves to turn yellow and die back. The roots also rot and the bulbs become covered with a fluffy white fungus.

Allium caeruleum (syn. A. azureum) has densely packed, globe-shaped flowerheads of star-like, flax-blue flowers among long, thin, mid-green leaves in early and mid summer. Set the bulbs 15cm (6in) apart. The flowers, carried on 60cm (2ft) high stems, are popular for cutting. Allium christophii (syn. A. albopilosum) is best grown among herbaceous plants to hide its untidy grey-blue leaves. Plant the bulbs 10-13cm (4-5in) apart. In early summer the large heads of striking, star-shaped, lilac-pink flowers appear on stems 60cm (2ft) tall. The seedheads that follow in autumn and winter are excellent for indoor dried flower arrangements. Allium giganteum stands well above most other herbaceous plants, often reaching an impressive height of 1.5m (5ft). It is grown for its large, decorative flowerheads: balls of mauve, star-shaped florets that appear in early summer. Like many of the ornamental onions, it has long, thin, grey-blue leaves. Plant 23-30cm (9-12in) apart. Allium moly forms a vivid display in early and mid summer with its bright yellow, star-shaped flowers on 30cm (1 ft) stems, among grey, lance-shaped leaves. It is particularly invasive, so avoid planting it among small, delicate plants. Space the bulbs 10cm (4in) apart. Allium oreophilum (syn. A. ostrowskianum) grows 30cm (1 ft) high. Planted 7.5cm (3in) apart, it can spread rapidly. The small, rose-coloured flowers and drooping, grey-blue leaves are excellent for enlivening rockeries in early summer. Allium roseum has elegant, rose-pink, star-shaped flowers in early summer. It grows 30cm (1 ft) high and has long, broad, mid-green leaves. Plant the bulbs 10cm (4in) apart.

Cultivation

Alliums grow best in well-drained soil in open sunny sites. Plant the bulbs in early to mid autumn in clumps of six or more for visual impact. Cover each bulb with soil twice its height – if the dormant bulb

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