Fundamental Facts
HARDINESS: Zones 4 to 8
PREFERRED SOIL pH: Near neutral
PREFERRED SOIL TYPE: Fertile, well-drained
PREFERRED LIGHT: Sun
ATTRIBUTES: Clusters of white, mauve, or purple flowers; for beds, cutting
SEASON OF INTEREST: Late spring to early summer and late summer
FAVORITES: A. aflatunense 'Purple Sensation', A. christophii, A. karataviense
QUIRKS: Requires cold winter dormancy period to initiate flowering
GOOD NEIGHBORS: Artemisia, hardy geranium, ornamental grasses, yarrow
WHERE IT GROWS BEST: Sunny, well-drained sites in regions with dry summers
POTENTIAL PROBLEMS: Wet soil rots the bulbs
RENEWING PLANTS: Lives many years; rejuvenation is generally unnecessary
CRITTER RESISTANCE: Excellent
PLANTING DEPTH: 5-8 in (12.7-20.3 cm) depending on species
SOURCE: Bulbs
DIMENSIONS: 8-36 in (20.3-91.4 cm) tall; flowers to 10 in (25.4 cm) in diameter
Ornamental Onion in the Landscape
If you think of onions as bulbs that make you weep, think again. Ornamental onions have but a faint onion scent and only if leaves are crushed. What they offer instead is beautiful flowers in shades of purple, lavender, mauve, and white. Individual flowers are clustered together atop sturdy stems, where they open in unison to create an impressive globe or an open star burst. Ornamental onions make great accent plants in the perennial border from late spring to summer, when most reach their pinnacle of beauty. And the flowers, both fresh and dried, are good for bouquets.
All in the Family
One of the easiest ornamental onions to grow is Allium aflatunense 'Purple Sensation'. The 3 ft (1 m) tall plant produces a dense, 4 in (10.2 cm) wide cluster of rich violet flowers. Because the leaves are skimpy, combine it with a full-foliaged bedfellow, such as yarrow or zinnia.
With its 6-10 in (15.2-25.4 cm) diameter flower clusters on 12-24 in (30.5-61 cm) tall stems, star of Persia (A. christophii) is suitable for the front of the border. Purple flowers with a silvery metallic sheen appear in late spring. Another big-flowered species is giant onion (A. giganteum), which has dense, 6 in (15.2 cm) purple clusters atop stems that can reach 4 ft (1.2 m).
Most ornamental onions have plain grassy foliage, but A. karataviense has wide, arching, lightly pleated blue-green leaves. Its mauve-pink flowers blend with everything from silver-leaved artemisia to hardy geraniums. Stems grow to about 8 in (20.3 cm) tall, topped by 3 in (7.6 cm) wide flower clusters. A. senescens also has attractive foliage. The gray-green leaves are loosely twisted and grow in a whorled clump, from which 2 ft (0.6 m) tall stems of mauve flowers emerge in late summer.
Another easy-to-grow allium, drumstick allium (Asphaerocephalum), produces its 2 in (5.1 cm) wide oblong clusters of reddish purple flowers on 3 ft (1 m) tall stems that sway in the breeze in early summer.
Growing Ornamental Onion
Plant allium bulbs in the fall in a sunny site with good drainage, otherwise the bulbs may rot. Dig a hole about 5 in (12.7 cm) deep for small bulbs, such as those of 'Purple Sensation', and 8 in (20.3 cm) deep for larger bulbs. Set bulbs in soil with the pointed ends up, in groupings of 3-5 for the smaller alliums or individually for the larger ones. Ornamental onions produce sulfur, the source of the characteristic onion scent, which naturally repels insect and four-footed pests. In fact, growing any member of the onion family near plants that usually attract pests can offer protection to the companions.
Alliums do not multiply quickly from bulbs, but some reseed. Seedlings look like grass and take several years to flower. If you don't want volunteers, cut off and dispose of old flowers as they fade to keep them from setting seed. Better yet, cut the flowers as they open for a bouquet.
Entries (RSS)