Alliums, ornamental onions, are unusual plants that add pizazz to any perennial bed. Find facts and information on growing allium bulbs.
The alliums, comprise several hundred species, related to the onion family. They grow from bulbs or bulblike rhizomes. The rhizome-rooted types need roots to spread. Some alliums are hardy, others are not. Most wholesalers sale only hardy varieties.
Many of the flowers have a sweet scent, unlike the garlic smell of a cut or bruised leaves. They look like chive blossoms, with each round flower cluster held on a single, straight stem.
Use smaller varieties in flower beds or rock gardens, and taller varieties in perennial borders or as accent plants.
Facts on Allium Bulbs
Plant type: Hardy or tender bulbs
Growing range: Zones 4 to 9
Hardiness: Varies by species, some are tender, many are hardy.
Plant Height: 6 inches to over 4 feet
Flower color: Yellow, white, cream, purple, pink, red, violet-blue.
Flower form: Tiny, lily-shaped flowers in rounded clusters.
Season of Bloom: Spring or summer for most, very short bloom time
Soil: Any well-drained soil.
pH: Near 7 (neutral)
Fertilizer: Well-rotted manure, bonemeal, slow-release fertilizer applied lightly
Water: Moderate, not too wet
Exposure: Sun or dappled shade under deciduous trees.
Spacing: 2 or 3” apart and deep to 12” apart, 8”deep, depending on type.
Propagation: Usually from bulbs, also from seed.
How to plant, transplant, and propagate alliums
- Start seeds indoors in late winter to early spring. Plant 1/8 inch deep,1/2 inch apart, in flats or one per pocket in six packs in bright light at about 60 degrees. The potting mix should be a third to a half sand. Seeds usually germinate in ten to thirty days. Some types need a freeze to break dormancy and may take up to a year to germinate. Plants are delicate at first, then gain strength.
- Prepare soil outdoors by digging the bed and turning in compost, fertilizer, sand (for drainage), and other soil amendments, as needed.
- Sow seeds outdoors a few weeks before the frost-free date or plant them in summer when seeds ripen. For some types, plant in fall in cold frames. Plant 1/8” deep, I “ apart, in finely tilled soil, in rows.
- Thin or transplant. When indoor-grown seedlings are a few inches tall, shift them to one plant per pocket of six-packs or to outdoor nursery beds. When seedlings grown outdoors become crowded, thin or transplant them to permanent positions. Most types flower in their second year.
- Set out bulbs. Alliums are most often grown from bulbs purchased and planted in fall. Plant according to package directions which are usually given along with the bulbs. Most types should be planted 3 to 5” deep. In specialty nurseries, alliums can sometimes be purchased in bloom in pots.
- Dig and separate crowded plants after they bloom, when foliage starts to yellow, being careful not to cut into the bulbs. After lifting a clump with a spade, tease the bulbs apart by hand. With special care, you can also move small, shallowly planted types in spring before they bloom or even while blooming (only if necessary).
- Water if needed while plants have green foliage. Do not overwater or bulbs will rot.
- Fertilize during active growth with bonemeal and all-purpose bulb or flower fertilizer.
- Pests and diseases rarely trouble the oniony alliums. If slugs are a problem, dust the ground with ashes and lime or diatomaceous earth, or trap the slugs in partly submerged pans of beer.
- Weed the bed in spring before plants come up.
- Stake large, tall types, if necessary, by tying each one to a slim bamboo stick.
- Remove flower heads and stems after bloom is finishes, unless seed is wanted. Let leaves disappear by themselves, or remove them when they are yellow. Mark the spot where your bulbs are planted because you can not tell where they are planted while dormant.
- Protect in winter. In areas with freezing winters, dig and store bulbs of any alliums that are not cold hardy. Refrigerate them in plastic bags filled with barely moistened peat until the danger of freezing weather has passed. Most types sold in the United States are hardy and need no winter care.