How to Grow Allium caeruleum Plants in your Garden

True blue flowers are such rarities that the flax-blue Allium caeruleum (seer-OO-lee-um) is a prized addition to any garden.

This species goes by the common names of Blue flower garlic, Blue globe onion and Bue-of-the-heavens.

It grows well in Hardiness zones 2 to 10 (UK H5, so hardy to about -15°C / 5°F).

It is a member of the Amaryllis family and is thus related to onions and garlic.

Although the leaves are not edible, they have a faint onion aroma when they are crushed.

Azure-flowered garlic
Allium caeruleum photograph by Col Ford and Natasha de Vere.

The plant is adorned with striking, one-to-two-inch (2.5 to 5 cm) pom-poms formed by clusters of small, vivid blue (azure) florets. The richly colored flowers perch on long, rigid stems that grow one to two feet tall (30 to 60 cm).

Allium caeruleum blooms from late spring to early summer> It has many uses in the garden as it repels deer, rabbits and rodents, but invites showy pollinators such as butterflies.

Since its slender leaves wither before flowering starts, and cannot be removed, it is a good idea to plant mid-height perennials in front of it to camouflage wilted foliage.

Allium caeruleum plants look dazzling when paired with yellow, peach, white or pink flowered plants.

They can be planted in borders, beds, rock gardens, cottage gardens and meadow-like gardens.

Gardener's HQ Guide to Growing Azure-flowered Garlic / Blue Globe Onion

Allium caeruleum is an undemanding perennial. It thrives in six to eight hours of full sunlight a day.

Well-drained soil is crucial to prevent bulbs from rotting.

Bulbs should be planted in the fall and fed with bulb fertilizer to promote optimum health and growth.

Plant them four to six inches (10 to 15 cm) deep at a spacing of approximately five inches (13 cm) apart.

For a lush look, plant the flowers in 12-bulb groups.

Although Allium caeruleum is drought-resistant it should be thoroughly watered after planting. Watering can resume in the spring.

The plant self-seeds, so flowers should be deadheaded to inhibit their spread.

Allium caeruleum Growing and Care Guide

  • Scientific Name: Allium caeruleum
  • Common Name: Azure-flowered garlic, Blue globe onion, Blue ornamental onion, Blue-of-the-heavens, Blue-flowered garlic
  • Growing Zone: USA: 2 to 7 for best results. UK: H5.
  • Life Cycle / Plant Type: Herbaceous, Perennial

Plant Details

  • Plant Height (Inches): 12 to 24
  • Plant Spread (Inches): 12 to 18
  • Time of Bloom: Late spring to Early summer
  • Flower Details: Blue
  • Leaf Foliage: Green
  • Fruit:
  • Growth Form: Upright / erect

Ideal Growing Conditions

  • Best Light Conditions: Full sunlight
  • Rate of Growth: Average pace
  • Suitable Soil Types: Loamy, Neutral, Sandy, Well drained
  • Soil Moisture: Dry

Caring Conditions

  • Care:
  • Level of Maintenance: Low
  • Propagation: Seed or clumps, 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, onion fly, thrips
  • Diseases: Mainly trouble free, Onion white rot and downy mildew

Further Information

  • Can Attract:
  • Tolerant of:
  • Best Garden Use: Container, Rock garden, Specimen
  • Family: Amaryllidaceae.
  • Closely Related Species: Agapanthus, Amarylis, Narcissus, Galanthus, Zephyranthes.

  • Miscellaneous: Non-native to North America, Suitable for cut flowers
  • Genus Detail: Allium
  • Further Reading and References: Here and Here

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