Bulb · Amaryllidaceae family
giant onion
Allium giganteum
In short a 10-second read
Giant onion (bulb) grows to 0.9–1.5 m tall and 0.45–0.6 m wide when mature. It grows best in full sun, in average soil. It flowers in June–July; the flowers are purple. Hardy to −29 °C.
× spread 0.45–0.6 m
Where to plant
Sun, soil, frost.
It grows best in full sun, in average soil. Hardy to −29 °C.
Sun
Elsewhere it will grow less well.
Soil and water
average · watering: moderate
Soil: loamy, sandy, clay
Soil pH 5.5–8.5
Frost
It copes with a normal winter outdoors.
How much space it takes
Mature size.
The mature plant next to a person (175 cm).
Next to a person
Reaches maturity in about 2–5 years. The final size depends on the cultivar and the spot — we give the range from smallest to largest.
Calendar
What to do and when.
Months for Central Europe. The line shows the current month.
The year at a glance
Flowers
June–July · purple
Planting
bulb: September–November
Winter protection
not needed
Overwintering
It copes with winter on its own.
It overwinters outdoors without protection, hardy to −29 °C.
- Needs no protection
- Hardy to −29 °C
- Dies back in winter and regrows in spring
What to combine it with
Same needs, different flowering.
They share the same sun and soil and flower in other months — so the bed flowers for longer.
Frequently asked
Quick answers.
When does giant onion flower?
In June–July; the flowers are purple.
Does giant onion tolerate shade?
No, it needs full sun.
How much space does giant onion need?
At maturity 0.45–0.6 m wide and 0.9–1.5 m tall; recommended spacing 58 cm.
Does giant onion survive winter outdoors?
Yes, without protection, hardy to −29 °C.
Where the data comes from
The data is indicative — we are still comparing it with further sources. Last checked 20 October 2026.
Show sources (18)
- Missouri Botanical Garden Plant Finder — Allium giganteum
- NC State Extension Gardener Plant Toolbox — Allium giganteum
- GBIF Backbone Taxonomy — Allium giganteum
- GBIF Occurrence Search API — Allium giganteum
- Wikidata (CC0) — Allium giganteum
- EPPO Global Database — Allium giganteum
- OBI.sk — „Cesnak obrovský
- Bamberger Staudengarten (Strobler), katalóg
- Foerster-Stauden, katalóg
- RHS - Bulbs: growing guide
- RHS: Allium giganteum
- Invasive plant lists — this species is not on them: EASIN, EU, Slovakia, Czechia, Germany, Poland, Denmark
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