How to Grow Schubert's Allium

Seed head of Allium schubertii.
David Beaulieu

Schubert's allium is one of several allium species grown as ornamental landscape plants, often called ornamental onions. Although closely related to chives and edible table onions, the various ornamental onions are mildly toxic plants for humans, and more seriously toxic to pets.

Schubert's allium is a spring-flowering bulb with strap-like foliage. While it has the same globe-shaped flowers found on other ornamental onions, the blooms on this species have a very striking resemblance to exploding fireworks. The flower heads are large globe-shaped clusters of 100 or more tiny star-shaped flowers—the entire globe can be as much as 18 inches across. The flower stems are sturdy enough to use in cutting arrangements. Despite the very dramatic appearance, Schubert's allium is remarkably easy to grow, making it a favorite among beginning gardeners seeking a spectacular plant.

Schubert's allium bulbs, like other ornamental onions, are normally planted in the fall in order to give them the cold-chilling period they need to bloom.

Botanical Name Allium schubertii
Common Names  Schubert's allium, ornamental onion, tumbleweed onion
Plant Type Perennial bulb 
Mature Size 12–24 inches tall, 12–18 inches wide
Sun Exposure Full sun
Soil Type Dry to average moisture, well drained loam
Soil pH 5.5 to 7.0 (acidic to neutral)
Bloom Time Late spring
Flower Color Rosy purple
Hardiness Zones 5–8 (USDA)
Native Area Palestine, Syria, northern Iran, western Turkestan
Toxicity Toxic to dogs and cats, mildly toxic to humans

Schubert's Allium Care

Schubert's allium, like most ornamental onions, is an easy perennial bulb to grow. Just about any sunny location with average well-draining soil will work for these plants. Shubert's allium is native to the dry regions of western Asia and will do best in conditions that mimic those regions. Give Schubert's allium plenty of space, as you do not want the foliage of other plants obscuring your view during its peak display time. Avoid planting it next to large plants that will swallow it up.

In mid-to late fall, plant the bulbs about 4 to 6 inches deep, spaced 12 to 18 inches apart. Bulb orientation in the hole is important. Look for either a point on the bulb or tiny roots. A point indicates the top of the plant, roots the bottom. Bury the bulb in the soil so that the top points up.

Blend bulb fertilizer into the soil around the buried bulbs and water it in. The strap-like leaves will appear first in early spring, followed by tall flower stalks will suddenly shoot up as spring draws to a close. As the globe-like clusters of star-shaped flowers open, the leaves will begin to wither; this is entirely normal.

The seed heads can be left on the plant as the flowers fade. The dried tumble-weed-like flowerheads can be quite attractive and sometimes will fall off the stems to blow around the garden. Self-seeding is common, though it may take several years for volunteer plants to develop the sizeable bulbs that produce their own flowers.

Schubert's allium is not affected by any truly serious insect or disease problems, but bulb rot can be a problem in very moist soils. Humid conditions can also foster mildew, rust, and leaf spots. Onion flies and thrips can sometimes be a problem; they are best treated with horticultural oil.

Photo of Schubert's Allium, an ornamental onion. Flower heads are jaw-dropping.
Ornamental onion picture. David Beaulieu
Ornamental onion (Allium schubertii)

 

James A. Guilliam/ Getty Images

Light

Ornamental onion species all require full sun in order to bloom—the more the better. They can survive some shade, though the leaves and flower stalks may be overly long and floppy in shady conditions.

Soil

These plants prefer dryish or medium-moisture loamy soils. Ordinary garden soil amended with peat moss to improve drainage is often ideal. Avoid dense, wet soils for this plant.

Water

Like many perennial bulbs, alliums don't require a lot of water; in fact, too much moisture will invite bulb rot. It's a good idea to water regularly in spring, but after blooming is complete, withhold water altogether. When feeding, the fertilizer should be thoroughly watered in.

Temperature and Humidity

Schubert's allium will do well in the temperature and humidity conditions through its hardiness range, zones 5 to 8. They often will survive in zone 4 if the bulbs are well insulated with mulch for the winter. These plants do not like extremely humid conditions, which can cause leaf spots and other fungal issues, though these problems are rarely life-threatening.

Fertilizer

Like most alliums, Schubert's does not normally require feeding if the soil has a good blend of organic material. With barren soils, an application of granular time-release bulb fertilizer in the early spring can be helpful.

Is Schubert's Allium Toxic?

Unlike the onion species grown for the table, ornamental onions are mildly toxic to humans and more seriously toxic to pets. All parts of the plant contain sulfides that can cause health issues.

Symptoms of Poisoning

Ingesting any of the plant parts of Schubert's onion may cause digestive problems, including nausea, vomiting, and diarrhea in humans. Treatment is usually unnecessary for humans.

In cats and dogs, ingestion can cause heart and breathing problems, as well as digestive symptoms even more severe than those experienced by humans. A vet will likely induce vomiting and introduce activated charcoal to neutralize allium toxins in pets that have consumed the plant.

Related Varieties

Though few species have flowers that rival the spectacular nature of Schubert's, there are several other ornamental onions that have largely the same cultural needs:

  • Allium sphaerocephalon is also known as drumstick allium. It has 1-inch flower clusters that bloom in early summer,
  • 'Globemaster' is a hybrid cross between A. christophii and A. macleanii. It has very tall, 3- to 4-foot flower stalks that support large 8- to 10-inch diameter flower globes.
  • 'Mount Everest' is another tall hybrid, though not quite a tall as 'Globemaster'. It blooms in a creamy white.
  • 'Purple Sensation' is another hybrid allium. Its flower stalks reach about 2 feet tall and support 2- to 4-inch globes of bright purple flowers.

Propagating Schubert's Allium

Spring-blooming alliums are generally propagated by digging up the bulbs in fall and breaking off the offset bulbs that form around the parent bulb or the flower stalk. These bulblets are produced rather slowly, so don't plan to dig them up every year. The offsets can be replanted at a depth of about three times the diameter of the bulb. Be patient, as it may take several years for the newly planted bulblets to develop the size necessary to produce their own flowers.

How to Grow Schubert's Allium From Seed

Schubert's allium often self-seeds from seeds dropped from the dried flower heads. The tiny volunteers left to grow in the garden will eventually develop their own bulbs and begin to flower, though this can take a number of years. The volunteers can also be transplanted to other locations.

Overwintering

In northern zones, you may want to apply a thick mulch over the pruned-back flower stalks to protect the bulbs over winter. This treatment sometimes allows Schubert's allium to survive as far north as zone 4. The mulch should be promptly removed in the spring to prevent rot.