Although it is a member of the onion, garlic and leek family, giant allium (Allium giganteum), also known as flowering onion, is grown for its big, lollipoplike clusters of lavender blooms. The softball-sized flowers appear on top of long, sturdy stalks in May or June. The blooms, which provide color between early blooming bulbs and summer annuals, last about three weeks if they aren't exposed to strong winds. Allium is appropriate for planting in U.S. Department of Agriculture hardiness zones 6 to 10, and survives even cooler climates with adequate winter protection. Once established, the plants require virtually no care.
Plant giant allium bulbs in fertile soil in an area that receives bright sunlight.
Water the planting area deeply, saturating the soil around the bulbs, immediately after planting. Once established, giant allium is drought-tolerant and no supplemental irrigation is required.
Feed giant allium at planting time to get the bulbs off to a healthy start. Use a fertilizer formulated for flowering bulbs, applied according to the directions on the package label. Once the giant alliums are established, no fertilizer is required.
Control allium by pinching flowers as soon as they wilt. If you want more plants, allow the flowers to go to seed.
Cut allium down to ground level after the foliage turns yellow in late summer. Avoid cutting the foliage while it's still green, as the living foliage provides the bulbs with energy for the following blooming season.
Spread 2 to 3 inches of mulch over the planting area in autumn to protect the bulbs and maintain an even soil temperature. Use an organic mulch such as compost, chopped leaves or shredded pine bark. Remove the mulch after the last frost in spring.
Divide giant allium every three to four years or when the plants begin to look overcrowded and blooming decreases. Lift the bulbs from the ground with a garden fork or spade. Pull the bulbs apart. Replant a few of the bulbs, and then plant the remainder of the giant allium bulbs in a new location.
Things You Will Need
- Fertilizer formulated for flowering bulbs
- Garden fork or spade
- Garden shears
- For an attractive display of color, plant giant allium bulbs in groupings of three bulbs per square foot.
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