Giant allium
Allium giganteum · Amaryllidaceae
Dense, lilac-purple spheres the size of a grapefruit on bare stems as tall as a person, in early summer.
- Size
- 5 ft tall, 12 in wide
- Zones
- 5 to 8
- Light
- Full sun
- Flowers
- Early June to late June
- Pets
- Toxic (moderate)
- Job in a bed
- Accent
A bed built around giant allium
The planner designed this bed around giant allium when this page was made: a 12 × 6 ft (3.7 × 1.8 m) English border in zone 6, full sun. It chose the other plants from the 715 that suit those conditions and its dry soil, and says below why giant allium stands where it does.
The plants
- 1 Cheddar pinks 'Tiny Rubies' × 19, pink
- 2 Leadwort × 9, blue
- 3 Wild quinine × 3, white
- 4 Stiff goldenrod × 3, yellow
- 5 Dwarf English boxwood × 1, dark green leaves
- 6 Coneflower 'Kim's Knee High' × 3, pink
- 7 Giant allium × 3, purple
- 8 Hyacinth × 8, blue
Why this plant
- The only globes. The others are open bowls, dense clusters, flat plates and others. Shape reads at a distance, where colours blur.
- The only purple.
Why here
- Anchors a back corner. At 5 ft it is the tallest plant here, and the tallest close the ends of the bed, where they stand in front of nothing.
- A step in the back row. Next to wild quinine (3½ ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- 3 plants in one clump. A single spire is too slight to hold a place alone, so here the accent is a clump.
Why now
- In flower for four weeks. From early June to late June.
- In company. With Cheddar pinks 'Tiny Rubies' and wild quinine in late June: 3 kinds at once.
- Leaves gone by midsummer. They die back and leave bare ground. A perennial that comes up late stands beside it, and grows over the gap.
Planned as an English border: 6 of the 7 groups (86%) are drifts, longer along the bed than they are deep. The flowering year starts with hyacinth in mid April and ends with leadwort in early October. Cheddar pinks 'Tiny Rubies', fine in leaf, stands next to bold-leaved stiff goldenrod, and each shows the other off.
The planner's own design check: 12 Excellent, 3 Good, 2 Satisfactory. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where giant allium goes in a border
At 5 ft it belongs at the back of a bed. In the planner's ten height classes it is tall (4 to 5 ft). It is airy enough to see through, so it can also come forward and veil what is behind it.
Its job: accent. An upright plant used singly, like a punctuation mark, and repeated at intervals to give the bed rhythm.
The tallest ornamental onion. The stems are bare, so the globes seem to float above the planting. The broad leaves are dying by flowering time and need neighbours to hide them.
- Tall exclamation marks above a border
- Cut and dried flowers
- A dramatic early-summer feature
What to plant with giant allium
Plants recorded as good partners for it, and what each pairing does:
- Peony: in flower together for three weeks, from early June; grows up in time to hide its dying leaves; medium leaves against its bold ones.
- Catmint 'Six Hills Giant': in flower together for four weeks, from early June; grows up in time to hide its dying leaves; fine leaves against its bold ones.
- Bearded iris: purple against yellow, opposite each other on the colour wheel, if you choose those colours, in flower together for two weeks; medium leaves against its bold ones; low enough (2½ ft) to stand in front of it.
Questions about giant allium
Does giant allium need sun or shade?
Giant allium grows in full sun (6 or more hours of direct sun a day).
It wants dry, sharply drained soil, of average fertility, and little watering once settled.
What zones does giant allium grow in?
USDA zones 5 to 8. It is hardy to zone 5, which means it survives winter nights down to about −10 °F (−23 °C).
Above zone 8 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does giant allium flower in my zone?
In zone 5 it flowers early June to late June. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 5 | Early June to late June |
|---|---|
| Zone 6 | Early June to late June |
| Zone 7 | Late May to late June |
| Zone 8 | Late May to late June |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should giant allium be planted?
10 in (25 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 12 in (30 cm), so a group knits into one patch.
It grows 5 ft (150 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many giant allium plants do I need?
At 10 in apart, set out in staggered rows:
- 17 to fill 10 square feet (about 1 m²)
- 13 for a single row 10 ft (3 m) long
- 55 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as one at a time, repeated along the bed at intervals; a slender one reads better as a clump of three.
In the bed above, the planner used three in one group.
Is giant allium poisonous to dogs and cats?
Yes: moderate toxicity to people, dogs, cats and horses. Like all onions, it can damage red blood cells in dogs, cats and horses if eaten. Eating the bulbs in quantity can also upset a person's stomach.
Rated from NC State Extension. Where references disagree, the more cautious rating is used.
Do deer eat giant allium?
Mostly not. NC State lists it as resistant to deer and rabbits. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.
What can I plant to hide giant allium's leaves after it flowers?
A bulb's leaves have to be left to yellow for about six weeks after flowering, to feed next year's flowers. Plant it among perennials that come up late and spread wide, and they grow over the leaves as they fade:
- Peony: 3 ft tall and 3 ft wide, a recorded partner, in flower late May to late June.
- Catmint 'Six Hills Giant': 3 ft tall and 3 ft wide, a recorded partner, in flower late May to early September.
- Blue false indigo: 4 ft tall and 4 ft wide, in flower late May to mid June.
What does giant allium look like in winter?
Giant allium is underground: it dies back after flowering and waits as a bulb until spring. Mark where it is, so a fork does not find it first.
Is giant allium good for bees and butterflies?
Giant allium is visited by butterflies.
More Allium
- Allium 'Ambassador' Allium 'Ambassador'
- Allium 'Gladiator' Allium 'Gladiator'
- Allium 'Globemaster' Allium 'Globemaster'
- Allium 'Mount Everest' Allium 'Mount Everest'
- Blue allium Allium caeruleum
- Chives Allium schoenoprasum
- Curly onion Allium senescens subsp. glaucum
- Drumstick allium Allium sphaerocephalon
- Garlic chives Allium tuberosum
- Golden garlic Allium moly
- Japanese onion 'Ozawa' Allium thunbergii 'Ozawa'
- Nodding onion Allium cernuum
- Ornamental onion 'Millenium' Allium 'Millenium'
- Ornamental onion 'Purple Sensation' Allium hollandicum 'Purple Sensation'
- Ornamental onion 'Summer Beauty' Allium 'Summer Beauty'
- Pink lily leek Allium oreophilum
- Schubert's allium Allium schubertii
- Sicilian honey garlic Allium siculum
- Star of Persia Allium christophii
- Turkestan onion Allium karataviense
In these guides
Zone guides: Zone 5 · Zone 6 · Zone 7 · Zone 8
In flower in: June
Every fact on record
- Type
- Bulb
- Size
- 5 ft (150 cm) tall, 12 in (30 cm) wide
- Plant
- 10 in (25 cm) apart
- Height class
- Tall (4 to 5 ft)
- Place in the bed
- Back, or further forward: it is airy enough to see through
- Flowers
- Early June to late June; globes; purple
- Leaves
- Bold texture, summer-dormant; green
- Shape
- Upright, clumping
- Hardy in
- USDA zones 5 to 8
- Light
- Full sun
- Soil
- Average, dry and sharply drained
- Water
- Low
- Feeding
- None needed
- Family
- Amaryllidaceae
- Comes from
- Himalayas, Western and Central Asia
- Attracts
- Butterflies
- Stands up to
- Deer, rabbits
Checked against NC State Extension. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.