How to Grow Allium giganteum Plants in your Garden

Gardener's HQ Guide to Growing Giant Onion

These tall, lofty perennials have a lush bright purple bloom that can help to add elegance and style to your garden.

Allium giganteum is a tall onion species native to Central Asia. The Allium genus iself is a genus that features every type of onion, from garlic through to shallots.

Giant onion

allium giganteum photograph by Manuel.

'giganteum' is the tallest species of the cultivated onions.

Though valued as an edible pant in Asia, in most gardens around the world this stately bloom is only planted its their decorative blossoms.

white and purple Allium giganteum plants
White and purple Allium giganteum plants, photograph by F. D. Richards; CC.

Gardener's HQ Guide to Growing Giant Onion

This plant requires a medium level of maintenance to perform at its best, and is particularly suited to US zones 5-8. They prefer warmer temperatures and strong sunlight during the day.

Be sure that soil is well drained but retains a trace of moisture. This will enable the Giant onions to better withdraw the nutrients necessary for proper growth.

If correctly taken care of, these plants can grow to be between three feet and five feet (90 to 150 cm). Allium giganteum grows best when grown in groups, so be sure to arrange them in at least a group of five.

Many gardeners choose these to line their flower beds, due to their columnar nature. They are also great as cut flowers in arrangements and emit a pleasant, leafy fragrance. They add a mysterious aura to a garden and can be used to great effect.

Giant Onion Flowers
Giant Onion Flowers, image by Neil; CC.

Allium giganteum Growing and Care Guide

  • Scientific Name: Allium giganteum
  • Common Name: Giant onion
  • Growing Zone: USA: 6 to 10
  • Life Cycle / Plant Type: Herbaceous, Perennial

Plant Details

  • Plant Height (Inches): 60 to 72
  • Plant Spread (Inches): 6 to 9
  • Time of Bloom: Summer
  • Flower Details: Pink, Purple
  • Leaf Foliage: Green
  • Fruit:
  • Growth Form: Upright / erect

Ideal Growing Conditions

  • Best Light Conditions: Full sunlight
  • Rate of Growth: Quick
  • Suitable Soil Types: Adaptable, Loamy, Sandy, Well drained
  • Soil Moisture: Moist

Caring Conditions

  • Care:
  • Level of Maintenance: Medium
  • Propagation: Seed, sowing in containers in a cold frame when just ripe or in the spring. Alternatively, remove offsets in autumn
  • How to Prune: Not usually required
  • Pests: Usually pest free
  • Diseases: Mainly trouble free, Onion white rot and downy mildew

Further Information

  • Can Attract:
  • Tolerant of: Rabbit, Deer, Black Walnut
  • Best Garden Use: Container, Foundation, En masse , Rock garden, Specimen
  • Family: Amaryllidaceae.
  • Closely Related Species: Agapanthus, Amarylis, Narcissus, Galanthus, Zephyranthes.

  • Miscellaneous: Attractive foliage, Fragrant foliage, Non-native to North America, Attracts butterflies, Suitable for cut flowers, Suitable for dried flowers
  • Genus Detail: Allium
  • Further Reading and References: Here and Here

Giant Onions growing in a field
Giant Onions growing in a field, photograph by cultivar413; CC.

I hope that you enjoyed this guide on how to grow Allium giganteum. You may also enjoy the following Gardener's HQ growing guides: How to grow Sternbergia and Zephyranthes plants.