Allium giganteum

Description

Allium giganteum – giant allium

Botanical name: Allium giganteum
Common names: Giant allium
Family: Amaryllidaceae
Plant type: Bulbous perennial
Habit: Upright, with rounded flowerheads on tall stems
Pot size: 2–3 litre pot
Eventual size: Approx. 1.2–1.5m tall × 20cm spread
Foliage: Strap-shaped grey-green leaves that often begin to die back around flowering time
Flowers: Large, dense, spherical heads of rich purple flowers on very tall stems in early summer (June)
Scent: Foliage has a mild onion scent when crushed
Aspect / light: Full sun
Soil: Well-drained; poor to average; dislikes wet; any pH
Hardiness: RHS H5 (hardy, to about −15°C); USDA zones 6–8
Exposure: Open, sunny; drought-tolerant
Native range: Species of ornamental onion, native to Europe and Asia
Toxicity / pet & child safety: Toxic to cats and dogs — like all onions and garlic, alliums can harm pets if eaten; also best not eaten by people

Allium giganteum, the giant allium, carries large, dense spheres of rich purple flowers atop very tall stems in early summer. Bold and architectural, it makes a dramatic statement in a sunny border.

GardenAdvice notes

An ornamental onion, this allium is grown for its striking, rounded flowerheads held on tall, strong stems in early summer, followed by decorative, long-lasting seedheads. Its bold, architectural flowers are wonderful in borders and a magnet for bees, and it is easy and drought-tolerant, thriving in any sunny, well-drained spot.

Growing & planting

Plant in autumn or spring in well-drained soil in full sun — alliums thrive on poor, dry, sunny sites and dislike wet, heavy ground. Their foliage often looks tatty by flowering time, so plant them among other perennials or grasses that will hide the leaves and set off the flowerheads. Space appropriately for their size.

Care & maintenance

Very low-maintenance. Allow the foliage to die down naturally after flowering, as it feeds the bulb for next year. Leave the seedheads standing, as they are highly decorative for weeks or even months. Cut down once they finally collapse. Established clumps can be lifted and divided when congested. They are drought-tolerant.

Propagation

• Division: Lift and divide congested clumps, separating the bulbs and offsets, once the foliage has died down.
• Seed: Species types can be raised from seed and often self-seed gently.

Pests & diseases

Generally trouble-free and easy. Bulbs can rot in wet, heavy soil, and allium leaf miner or onion white rot occasionally occur. Otherwise robust and reliable in a sunny, well-drained spot.

Uses in the garden

Superb dotted through sunny, gravel, prairie-style and mixed borders, among perennials and grasses that hide their fading foliage, and left standing for their sculptural seedheads; the flowers and seedheads are excellent for cutting and drying.

Wildlife value

Alliums are superb bee plants: their nectar-rich flowerheads are hugely attractive to bees, butterflies and other pollinating insects in early summer.

Toxicity & safety

Ornamental onions are toxic to cats and dogs if eaten — like all onions and garlic — and are best not eaten by people either, so site them with pets in mind.

GardenAdvice tip

As the name suggests, this is the giant of the alliums — big dense purple globes held way up on tall stems, making a real architectural statement floating above the border. Plant it in a bold group among lower perennials that will hide its rather untidy fading foliage, and leave the seedheads standing for weeks of extra sculptural interest.

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