Allium giganteum aka Giant Onion

Allium giganteum is a bulb-forming perennial known as giant onion. It belongs to the amaryllis family, Amaryllidaceae. Its native range spans northeast Iran and Central Asia. It grows upright, with leaves clustered around the base. Garden plants reach about 3–5 feet [0.9–1.5 metres] tall. Some sources report 6–8 feet [1.8–2.5 metres]. Clumps spread about 1–2 feet [0.3–0.6 metres].

The long, flat leaves have a green to gray-blue tint. They form a rosette and may spread across the ground. Reported leaf lengths range from 1.5–3 feet [0.45–0.9 metres]. Bruised leaves give off an onion-like smell. Smooth green scapes rise above the leaves without foliage. The leaves fade as flowering starts, or soon afterward. This leaves the flower heads standing above bare ground.

Each scape holds a round umbel of many small flowers. Each star-shaped flower has six parts. Flower colors range from lilac and purple to pink. Chicago Botanic Garden also records rare white flowers. The heads measure about 0.3–0.5 feet [0.1–0.15 metres] across. Bloom dates vary from May through July among sources. NC State reports a display lasting two to three weeks. Capsules follow the flowers. The blooms draw butterflies and suit fresh or dried arrangements.

Grow this onion in full sun and soil that drains well. It accepts acidic, neutral, and alkaline soils. Keep the soil moist while the plant grows. It can withstand dry spells in summer after growth ends. Shelter the tall stems from strong winds; they may need support. Plant bulbs in fall and divide mature bulbs to increase plantings. USDA ratings span zones 4–8, though Missouri lists 5–8. The RHS gives it a UK rating of H5. Groups work well toward the rear of a border. Nearby daylilies or low grasses can cover the fading leaves. Deer and rabbits tend to leave it alone.

Wet soil can lead to bulb rot and other fungal trouble. Listed pests include bulb mites, allium leaf miner, and onion fly. Onion white rot and downy mildew may also occur. Sources disagree about its tendency to spread and its safety. Plants For A Future lists bulbs, leaves, and flowers as edible. Missouri notes that gardeners do not use it as food. NC State warns of poisoning in people, cats, and dogs. Eating it may cause nausea, vomiting, or diarrhea. These conflicting reports make its food use uncertain.