Contact: Diane Relf, Extension Specialist, Environmental Horticulture
Posted April 1997
Allium giganteum, commonly known as the ornamental onion or giant onion, is a great eye catching plant. For approximately three weeks in June, it displays large, deep lilac flower balls about 4-5 inches in diameter on graceful, leafless stalks rising from the midst of the foliage. Its bluish-green foliage is hollow and straplike, growing about a foot and a half long with each leaf approximately two inches wide. This member of the amaryllis family can reach a height of three and a half feet, making it ideal for background plantings in a bed or border.
The bulb of the ornamental onion should be planted in fall (September to October) six inches deep in well-drained areas which receives full sun. Each should be placed 12-18 inches apart, or 10 bulbs per square yard, to insure sufficient room for growth. The plants should be lightly fertilized when the leaves first emerge. Following package instructions, spread a complete fertilizer on the soil or mulch. Spring rains will wash it down to the roots. Keep the soil moist throughout the growing season. In the winter the bulbs require cold nights with soil temperatures below 45 degrees F.
The ornamental onion is usually propagated from a bulblet, a little bulb that grows at the base of the original bulb. The bulblets may be separated from the mother bulb in early fall. It is also reproduced by seed. The seedlings may require three years before flowering whereas the bulblet usually takes only one. Unlike several other Alliums, A. giganteum will not become invasive.
The ornamental onion grows well throughout Virginia without any special growth requirements. Although it is a tall plant, staking need not be considered except in especially windy areas. Pest problems are practically nonexistent. For these reasons, Allium giganteum is an especially interesting plant to include in an outdoor garden. Its ornamental value can extend indoors as a long-lasting fresh cut or dried flower.
(Prepared by Ellen Silva, Program Support Technician, Environmental Horticulture, Virginia Tech, Blacksburg, VA 24061-0327.)
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