Scientific Name
Allium caeruleum (A. azureum)
Common Name
Ornamental Onion
ALLIUM
caeruleum (azureum)
(Blue flowers)
A. Flowering Characteristics
A. caeruleum flowers in very late spring (May/June) and lasts 2-3 weeks. Plants are 20 inches tall with small multi-flowered umbels.
B. General Characteristics
1. Origin of species: North to Central Asia
2. Common names: Ornamental Onion
3. Geophyte organ: Tunicated bulb
4. Hardiness type: Hardy II - Injured at temperatures below 14 degrees F (-10C) when planted.
5. Natural reproductive systems and growth and development requirements: A. caeruleum reproduces by annual daughter bulb replacement and seed and requires a warm (68 to 73F) - cool (28 to 32F) - warm (60F) annual thermoperiodic cycle.
6. Primary uses: Perennial beds, rock gardens, meadows, ground covers, and fresh cut flowers.
C. Cultural Information
1. Bulb sizes: 4/5 and 5/up cm, in circumference.
2. Planting density: 2 inches apart, 15-25 bulbs per sq. ft.
3. Planting depth: 5 inches to base of the bulb.
4. Planting time: Fall
5. Climatic zone habit: 1990 USDA Climatic Zone 4 with mulch, Zones 5 to 7 hardy without mulch.
6. Light requirements: Full sunlight only.
7. Moisture: Tolerates summer drought, but requires moisture during growing season.
8. Animal susceptibility: Normally not susceptible.
D. Companion Plants:
Alyssum, Baptisia, Dryopteris erythrosora, Coreopsis, Hemerocallis, Iris (rhizomatous), Kniphofia, Peonies, Stokesia, Verbascum, Acer palmatum, Buddleia, Cotoneaster, Deutzia gracilis, Kalmia, Rhododendron spp., Spiraea spp., Viburnum, Weigela.

Holland Technical Service Bulletin Number 31 was prepared for the WWW system by A.A. De Hertogh, L.B. Gallitano, M.E. Traer, and A.B. Russell, Department of Horticultural Science, NC State University. The information was obtained not only from original research conducted by the authors but also from databases released by other sources. This Bulletin was published by the International Flower Bulb Center (IBC), Hillegom, the Netherlands on behalf of the Dutch Flower Bulb Industry. Because of the various climates in North America and year-to-year variability of the weather, the IBC cannot and does not accept responsibility for divergent results that may arise using information obtained from this document or site. Photographs copyright @1997 by A.B. Russell and A.A. De Hertogh. Computer programming by Miguel Buendia, graphics by Brad Capel.