Ornamental allium Allium giganteum
Ornamental allium (Allium giganteum) is a deciduous perennial flowering plant in the Amaryllidaceae family. It grows 80 cm–1.5 m (31 in–4.9 ft) tall and 20–40 cm (8–16 in) wide, wants full sun and low water, and is hardy to about -25 °C (-13 °F). Space plants about 30 cm (12 in) apart.
Plan Ornamental allium in your garden →
Free. Draw your beds, then watch it grow through the year in 2D and 3D.
Ornamental allium at a glance
| Type | Perennial flowering plant, deciduous |
|---|---|
| Family | Amaryllidaceae |
| Mature height | 80 cm–1.5 m (31 in–4.9 ft) |
| Mature spread | 20–40 cm (8–16 in) |
| Spacing | 30 cm (12 in) centre to centre |
| Sun | Full sun, at least 6 h of direct sun a day |
| Water | Low; drought tolerance moderate, waterlogging tolerance none |
| Cold hardiness | About -25 °C (-13 °F) once established (roughly USDA zone 5) |
| Heat stress | Likely above about 32 °C (90 °F) |
| Flowering | from about May for 3–5 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Low |
| Pollinator value | High |
| Edible | Not grown as food |
| Common in gardens of | 🇬🇧 United Kingdom, 🇩🇪 Germany, 🇺🇸 United States, 🇳🇴 Norway, 🇳🇱 Netherlands |
Is Ornamental allium toxic?
- People: mildly toxic
- Cats: moderately toxic
- Dogs: moderately toxic
- Parts: bulbs, leaves
Alliums can damage red blood cells in cats and dogs and upset the stomach in people.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Ornamental allium
No well-documented helpful pairing. Group it with plants that like full sun and low water.
Keep apart or take care
- caution With Legumes (pea family): Onions, garlic and leeks are said to stunt beans and peas (allium root exudates may reduce nodulation). Traditional companion-planting advice; controlled trials are few, so treat it as a soft preference. Evidence D
- caution With Legumes (pea family): Beans and peas are traditionally kept away from onions, garlic and leeks. Traditional companion-planting advice; controlled trials are few, so treat it as a soft preference. Evidence D
Shared pests and diseases
- White rot: Allium white rot survives in soil for 15+ years; never move infected soil. Evidence B
See Ornamental allium in a botanical garden
It grows in this sample garden, which you can walk through in 3D:
- Riverside botanical garden (18 plants)
Questions about Ornamental allium
- How far apart should I plant Ornamental allium?
- About 30 cm (12 in) apart, centre to centre. A mature plant spreads 20–40 cm (8–16 in).
- Does Ornamental allium need full sun?
- Full sun: at least 6 hours of direct sun a day.
- How much water does Ornamental allium need?
- Low water. Drought tolerance is moderate and waterlogging tolerance none.
- How cold-hardy is Ornamental allium?
- It tolerates about -25 °C (-13 °F) once established, roughly USDA zone 5.
- When does Ornamental allium flower?
- From about May for 3–5 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Ornamental allium poisonous to cats and dogs?
- For cats it is moderately toxic; for dogs moderately toxic; for people mildly toxic. Alliums can damage red blood cells in cats and dogs and upset the stomach in people.
- What grows well with Ornamental allium?
- There is no well-documented companion pairing for Ornamental allium. Group it with plants that like the same sun (full sun) and water (low).
Sources and evidence
Evidence grade C (C: plausible, mixed evidence).
- ASPCA Toxic and Non-Toxic Plant List, ASPCA
- FAO Irrigation and Drainage Paper 56 — Crop Evapotranspiration, FAO
- RHS Plant Finder, Royal Horticultural Society
- University extension gardening guides (general), Various land-grant university extensions
Notes and assumptions
- Typical garden-cultivar values; varieties differ.
- Foliage dies back as the flower heads open.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Onion Allium cepa
- Daffodil Narcissus pseudonarcissus
- Garlic Allium sativum
- Leek Allium ampeloprasum (Porrum group)
- Chives Allium schoenoprasum
- Agapanthus Agapanthus praecox
- Shallot Allium cepa var. aggregatum
- Welsh onion (scallion) Allium fistulosum