Allium

( AL - ee - um )

At-A-Glance Information

Hailing from the Northern Hemisphere, the Allium genus encompasses over 500 species of perennials. These ornamental flowers need full sun to partial shade and regular waterings during growth and bloom periods. Plants in this group make fantastic cut flowers, provide playful charm, and are typically used in containers as well as in rock gardens. Flowers are borne in clusters at stem tips that can be between 6 inches to 5 feet in height. Flower color varies from white, pink, rose and violet to red, blue, and yellow. Alliums are loved by bees and other pollinators. Take care when planting Allium in the landscape, as plant parts are toxic to animals if ingested. For crop varieties of Allium (those cultivated for consumption), see the following page:

Allium Species and Varietals

Allium plants represent the largest genus in the Amaryllidaceae family, and are named after Garlic (the Latin word for garlic is allium). The genus was first officially described by Carl Linnaeus in 1753, and includes both ornamental species and those grown as crops. Growing zones for ornamental Allium vary by species; see the descriptions below for more information. To find your zone, click here: Zone Map.

Allium aflatunense (Persian Onion)
This species grows best in USDA growing zones 4-8 or Sunset growing zones 2-24. Lilac to pink flowers bloom in clusters at the end of 2.5 to 5 foot tall stems in springtime. Plants can tolerate winter temperatures down to -20 to -30 degrees Fahrenheit.

​Allium atropurpureum (Purple-Flowered Onion, Dark Purple Onion, Scallion Purple Flower)
Grows best in USDA growing zones 3-8 or Sunset zones 1-24. Stems up to 2.5 feet tall carry 2-inch clusters of dark purple to blackish flowers all summer long. This species is native to Hungary, the Balkans, and Turkey, and is widely grown around the world as a garden ornamental.

​Allium caeruleum (Allium azureum) (Blue Allium, Blue Globe Onion, Blue Ornamental Onion, Blue-Flowered Garlic, Blue-of-the-Heavens)
Blue flowers bloom in clusters atop 1-2 foot tall stems in late spring. Grows best in USDA hardiness zones 4-8 or Sunset zones 1-24. The species is native to central Asia, where it grows on dry slopes and in plains.

​Allium carinatum pulchellum (Allium pulchellum) (Keeled Garlic, Witch's Garlic)
This species grows best in USDA growing zones 3-10 or Sunset zones 3-24, and produces clusters of red-purple flowers on 2-foot tall stems in summertime. A white-flowered form of this species is commonly cultivated, as well. These plants are native to the Mediterranean Region, and have naturalized in the British Isles.

Allium cristophii (Allium albopilosum) (Star of Persia)
Grows best in USDA growing zones 3-8 or Sunset zones 1-24; Blooms in late spring with large clusters of lavender to deep lilac flowers shaped like stars. Flowers have a sheen to them, and are set on top of 12-15 inch stems. Leaves are long and green on top, white and hairy underneath. Great as dried flowers.

​Allium giganteum (Giant Allium, Giant Onion, Giant Leek)
Great in USDA hardiness zones 4-8 or Sunset growing zones 2-24, this summer bloomer produces clusters of flowers that are about the size of a softball. Flowers are bright lilac-colored and sit atop 5-foot tall stems. This species is native to central and southwestern Asia, and is cultivated worldwide as a garden ornamental.

​Allium 'Globemaster'
This is a popular varietal produces clusters of deep violet flowers to 8 inches across in summertime. Stems are 2.5 feet tall. Grows best in USDA hardiness zones 3-8 or Sunset growing zones 2-24.

​Allium karataviense (Turkistan Allium, Ornamental Onion, Ivory Queen Allium)
These grow best in USDA hardiness zones 4-8 or Sunset zones 1-24, and bear large, dense flower clusters in mid-spring. Flower color varies from pink to beige to red-lilac. This is one of the shortest Allium species, and is great for bordering walkways and at the front of mixed beds. Can also be grown in containers. 

​Allium moly (Golden Garlic, Lily Leek, Yellow Garlic)
This species is grown in USDA hardiness zones 3-9 or Sunset growing zones 1-24. It produces bright yellow flowers that appear to almost shine which are held in clusters on stems 6-10 inches tall. Blooms in late springtime. Variety 'Jeannine' blooms earlier in spring with 3-inch diameter flower clusters.

Allium narcissiflorum (Piedmont Garlic, Narcissus Onion, Pink-Flowering Onion, Narcissus-Flowered Onion)
Grows best in USDA hardiness zones 4-8 or Sunset zones 3-24, and produces foot-tall scapes topped with clusters of bell-shaped, bright rose-colored flowers. These ornamentals are perfect for rock gardens or small spaces, and also do well in containers. 

Allium neapolitanum (White Garlic, Neapolitan Garlic, Daffodil Garlic, False Garlic, Flowering Onion, Guernsey Star-of-Bethlehem, Wood Garlic)
Grows best in USDA hardiness zones 7-10 or Sunset growing zones 4-24. 1-foot tall stems hold spreading clusters of white flowers. This species is grown commercially for cut flowers. Varieties include 'Grandiflorum' (with larger blooms earlier in the season), and those in the Cowanii Group, which are considered superior (hardier and more pleasing to the eye as cut flowers).

​Allium oreophilum (Allium ostrowskianum) (Pink Lily Leek, Alpine Rosy Bells, Mountain Lover)
Grows best in USDA hardiness zones 4-9 or Sunset growing zones 1-24. Forms large, loosely-held clusters of rose flowers on 8-12 inch stems in late spring. Each plant produces only 2-3 grey-green leaves, Variety 'Zwanenburg' has deep red flowers on 6 inch stems, and is great for cutting for use in arrangements. This species is native to central Asia. 

Allium rosenbachianum (Showy Persian Onion, Showy Onion, Rosenbach Onion)
Similar to Allium giganteum but slightly shorter (2-3 foot tall stems). Flowers bloom in late spring. Variety 'Album' has greenish-white flowers. These ornamentals do well in USDA hardiness zones 4-8.

​Allium schoenoprasum (Chives, Wild Chive, Flowering Onion)
This edimental species grows well in all zones; forming clumps up to 2 feet tall of green, grass-like leaves that are hollow. Clusters of rose-purple flowers appear in spring. Great as an edging for a flower bed or herb garden, and also does well in containers. Leaves can be chopped or snipped, and are used as a garnish for dishes. Taste is similar to onion, but more delicate. 

​Allium sphaerocephalon (Drumsticks, Round-Headed Garlic, Bald-Head Onion, Round-Headed Leek)
This species grows best in USDA hardiness zones 3-8 or Sunset zones 1-24. It forms tight, dense flower clusters that hold reddish-purple blooms. Flower stems are about 2 feet tall. Spreads freely via seed.

​Allium tuberosum (Chinese Chives, Garlic Chives, Oriental Garlic, Asian Chives)
Grows in all zones, and forms grey-green clumps of flat leaves, and in summer blooms abundantly with clusters of white flowers. Blooms smell of violet, and leaves have a mild garlic flavor, making these plants edimental superstars. They do well in containers.

​Allium unifolium (Oneleaf Onion, American Garlic)
Native to California, this species grows best in USDA hardiness zones 3-9 and Sunset growing zones 3-9 and 14-24. Lavender to pinkish flowers are satiny and bloom atop 1-2 foot tall scapes in late spring. Spreads freely but is not considered invasive.

Caring for Allium

Ornamental Allium is typically purchased as seed or bulb, and planted in fall. Place bulbs three times their height deep in well-draining soil in a sunny location. Seeds can be direct-sown in the garden or started indoors. Spacing is dependent on the mature size of plants, ranging between 3 and 18 inches for best coverage and airflow. Ensure that soil is well-draining, rich in nutrients, and has a pH of between 5.5 and 6.5 (slightly acidic). If local soils are particularly poor in nutrients or do not drain well, make sure to amend the planting area with plenty of organic compost before installing. Apply a layer of mulch around the planting area to suppress weed growth, maintain consistent soil temperatures, and to increase soil moisture retention. Water new plantings regularly as they establish a strong root system in their new home. At maturity, they are drought-resistant ornamentals that appreciate deep waterings whenever the top 2-3 inches of soil feels dry to the touch. Do not allow Alliums to sit in soggy soil for too long, as these conditions will quickly lead to bulb rot.

Fertilize yearly in early springtime with an application of 2 inches of compost around the base of plants. Pull mulch back before applying, work the compost gently into the soil a bit, water it in, and then replace mulch. These plants are not heavy feeders, and this should be sufficient to provide the necessary nutrients for the active growing and flowering seasons. Most species will go dormant in summertime when temperatures begin to heat up, and do not have a repeat bloom when deadheaded. Flowering stalks can be removed to improve the aesthetics of the plant and discourage re-seeding. Remove foliage once it dies all the way back and turns brown. These ornamentals will last for 3-4 years or more in the landscape before needing to be divided to maintain health. For instructions on how to successfully divide Allium, see the Propagation section below.

Harvesting Allium
Ornamental Allium plants are harvested for their beautiful flowers, which add architectural interest and playfulness to arrangements. Taller varieties may need netting to prevent them from falling over as they grow and flower heads mature. To harvest, choose scapes that have at least a few florets are open in the flower head, cutting them in the morning after dew has dried but before the heat of the day sets in. Use clean, sharp shears or snips to cut stems, and drop them into a bucket of water. Ornamental Allium has a vase life of between 5 and 14 days. Alternatively, flowering heads can be left on plants to turn brown and dry out for use in dried wintertime arrangements. 

Propagation

For bulb-forming or rhizomatic Allium species, propagation is best done through division or by harvesting and sowing seed. For more information on how to propagate your Allium plant, read the instructions below:

Propagating Allium by Seed
If you are choosing this method of propagation, keep in mind that the resulting plant may not be a clone of its parent. To get an exact replica of the plant you are propagating, choose the division method of propagation instead. You will need a pot or tray (at least 6-8 inches deep), potting soil, compost, and a spray bottle filled with water.
  1. Gather your materials. The best time to harvest Allium seeds is in mid to late summer. You'll know your Alliums are ready to be harvested when the spent flower heads resemble the image at the bottom of the propagation section below. Take the seeds out of their pods, and set them aside. They should be stored in a cold, dark, dry place until you are ready to plant them. The ideal time to plant your seeds is in February, so that they will be ready to be transplanted outdoors in April.
  2. Prepare your pot or growing tray by filling it with potting medium amended with compost. Place your seeds on top of the potting mix, spaced about 2 inches apart. Sprinkle more amended potting medium over the top until the seeds are covered by a quarter of an inch. As the seeds are starting out, it is best to use a spray bottle to add moisture to avoid uncovering their light soil topping. Keep the soil moist as the seeds develop. Allium seeds germinate best at room temperature, and it should be just about a week to a week and a half when you start seeing green pop out from the soil. 
  3. Once the chance of frost has passed by, seedlings can be transplanted to a sunny area of the garden. Keep the soil moist as the plant develops and enjoy watching your Allium grow. 

Propagating Allium by Rhizome or Bulb Division
​This is a simple method of propagation, and can be done in spring or fall. Allium that grows from bulb will produce smaller bulbs on the sides of their existing bulbs. Those growing from rhizome can be divided easily with a shovel. To complete this method of propagation, you'll need a clean shovel, clean pruning saw (optional), extra pots if you are not going to immediately plant your divisions in the ground, and well-draining soil to fill the pots. To propagate your Allium by division, follow the instructions below:
  1. Identify the area of plants you're going to divide. Start by loosening the soil around the plant with your shovel, working your way inward to avoid causing damage to the roots or bulbs. Once you've gotten your clump out of the ground, lay it out on its side.
  2. Divide the clump of rhizome rooted Allium into segments, either with your shovel or with a pruning saw, as many as you'd like as long as there are at least three 'shoots' per segment, and lay them out on the ground. For bulb division, separate the smaller bulbs from the side of your main bulb clump, and lay them out on the ground. 
  3. If you will be planting your Allium in the ground, this is when you'll prepare your new hole. Dig a hole (large enough to accommodate the root ball or bulb) in the ground with your shovel in a sunny location with soil that is well-draining. Backfill and water generously.
  4. If you are transporting your division elsewhere, or hanging on to it until you're ready to plant it or share it with a fellow gardener, you'll need your pot filled with potting soil. Dig a hole large enough to accommodate the root ball or bulb, and place your new plant in the soil. Water generously, ensuring that adequate drainage is occurring. Place the pot in a sunny location until you are ready to plant it in the ground.​
Dried flower heads of the Allium plant ready to be harvested for their seeds.
Allium seeds are small and black.

Problems and Pests

Allium plants are relatively easy to care for, but do have their share of issues, including:
  • Allium Leafminer
  • Onion Maggots
  • Lesser Bulb Flies
  • Wireworms
  • Pinkroot
  • Fusarium Bulb Root
  • Onion Yellow Dwarf Virus
  • Neck or Bulb Rot
  • Smut
  • Onion Smudge
  • Purple Blotch
  • Rust
  • White Rot
For more information on these issues and how to solve them, see the links below:
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Gallery

Allium bulbs ready to be planted.
Alliums are great for bordering lawns, providing color and height to otherwise monochrome landscapes.
Plant Allium behind plants that are taller than its foliage; once the foliage dies, these plants will provide screening for spent leaves.
Children love Allium - especially the larger varieties. They can turn your garden into a wonderland.
Smaller varieties do great when planted in large groups, creating swaths of color throughout the garden.
Chives are a great, colorful addition to any herb garden, and taste great to boot!

Videos

How to plant, grow and care for Allium.
All about Alliums!
A wonderful video about Alliums and how to use them in the garden.

Resources

Allium Pests and Diseases
How to Grow Alliums
Planting, Growing, and Caring for Flowering Onions
Starting Alliums from Seed
Allium Plant: How to Grow Alliums in Your Flower Garden
Wikipedia: Allium
The New Sunset Western Garden Book: The Ultimate Gardening Guide (2012) - Pages 143-144, Allium