Giant Allium
Allium giganteum
Also called ornamental onion, flowering onion and giant onion
Giant Allium blooms from May through June.
Mature size, hardiness zones, sun and the trait tags were checked against named botanical sources for this plant. The bloom months and water need on this page were not.
Growing Giant Allium
Plant it in full sun. It prefers low water. It is hardy in USDA zones 4–8. Expect it to reach about 3 ft tall and 8 in wide at maturity, in roughly 1 year.
When to plant Giant Allium
Giant Allium is a fall-planted bulb: get it in the ground 6 to 8 weeks before the ground freezes, typically September or October across zones 4 to 8. It pays you back the following May to June.
Month-by-month timing for your zone is on the planting calendar: for the middle of its range, start with zone 6 in September.
8 more colors in the Allium family
Same family, similar care - pick the one you are growing.
Good to know about Giant Allium
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note.
Safety
Toxic to dogs, cats and horses: onion-family compounds damage red blood cells, causing Heinz-body hemolytic anemia. Cats are the most sensitive, and signs can lag days. per ASPCA and Merck
Worth knowing
The oniony smell does double duty: the same sulfur compounds that repel browsing deer are the toxins that poison dogs, cats and horses. per Clemson and Merck
Coldest zone varies by source
NC State lists it hardy to zone 4; Missouri Botanical stops at zone 5. Treat zone 4 as marginal: wet soil, not cold, is what kills the bulb. per NC State and Missouri Botanical
Draws bees and butterflies
The nectar-rich globe of many small florets draws bees and butterflies, a useful forage plant in late spring to early summer. per NC State and Wisconsin
Hardy bulb, no lifting
Plant dormant bulbs in fall, pointed end up, then leave them in the ground: they are hardy and, unlike dahlias or gladiolus, never need digging up for winter. per Iowa State and NC State
Comes back and multiplies
Ornamental alliums perennialize and many naturalize: they return year after year and spread slowly by offsets, and reseeding types self-sow. per Iowa State and Wisconsin
Allium leafminer pest
In the mid-Atlantic and Northeast, an invasive fly tunnels the leaves and bulb. Float row cover over its two flights, early spring and late summer, to exclude it. per University of Maryland and UMass
What pairs well with Giant Allium
Good companions share its growing conditions and add something it lacks: an earlier or later bloom, a lower carpet in front, or structure through winter.
Globe Thistle
Shares full sun and low water; blooms in midsummer as this one finishes; both are strong pollinator plants, and they feed in different months; its seed heads stand through winter, for structure and the birds.
Blazing Star
Shares full sun and low water; blooms in midsummer as this one finishes; both are strong pollinator plants, and they feed in different months; its seed heads stand through winter, for structure and the birds.
Black-Eyed Susan
Shares full sun and low water; blooms in midsummer as this one finishes; both are strong pollinator plants, and they feed in different months; its seed heads stand through winter, for structure and the birds.
Lavender
Shares full sun and low water; overlaps, then carries the display into late summer; both are strong pollinator plants; evergreen, so the bed keeps its shape through winter.
Sunflower
Shares full sun and low to moderate water; blooms in midsummer as this one finishes; both are strong pollinator plants, and they feed in different months; its seed heads stand through winter, for structure and the birds.
Passionflower
Shares full sun and low to moderate water; blooms in midsummer as this one finishes; both are strong pollinator plants, and they feed in different months; climbs to 13 ft behind it, height without the footprint.
Grape Hyacinth
Shares full sun and low water; blooms in early spring, before this one opens; both offer pollinator forage, in different months; lower at 8 in, for the front of the border.
Butterfly Bush
Shares full sun and low water; overlaps, then carries the display into early fall; both are strong pollinator plants; taller at 6.6 ft, for the layer behind it.
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