Globemaster ornamental onion

Sun

Full sun; flowering is weaker and stems may lean in shade.

Water

Water during active spring growth if the soil becomes dry. Once the leaves die back, keep watering to a minimum; avoid persistently wet soil in any season.

Soil

Well-drained sandy, loamy or gritty soil. Heavy clay needs improved drainage or a raised bed; avoid sites that stay waterlogged.

Height

2.5-3 ft (0.75-0.9 m)

Spread

1-1.5 ft (0.3-0.45 m)

Flowers

Late spring to early summer; dense violet-purple globes commonly 8-10 in (20-25 cm) across.

Foliage

Broad, strap-shaped, grey-green basal leaves emerge in spring and often begin yellowing by flowering time. The plant becomes dormant in summer.

Growth

Moderate; established bulbs flower annually and gradually form larger clumps.

Care needed

Low

• Pollinators
• Deer resistant
• Drought tolerant
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Easy

Toughness

Very tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   0.5 ft (0.15 m)

2. After 1 year

   2.7 ft (0.83 m)

   full size

About 1 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Toxic

Growth rate

Moderate

• Plant bulbs in autumn, with their bases about 6-8 in (15-20 cm) deep and centres 10-12 in (25-30 cm) apart.
• Water during prolonged dry spells while leaves are green, but do not routinely irrigate dormant bulbs.
• Apply a light dressing of balanced fertiliser as growth starts in spring if the soil is poor; avoid heavy nitrogen feeding.
• Keep thick, wet organic mulch away from the bulb crowns and improve drainage before planting in heavy soil.
• Divide congested clumps after the foliage dies back, usually only every few years; replant sound bulbs promptly.

Pruning. Leave the flower heads standing for their dried shape, or cut the stems at the base after flowering. Remove leaves only once they have yellowed and died back naturally.

Autumn

Plant bulbs in a sunny, freely draining position.

Winter

Check that water is not collecting over the bulbs, particularly in heavy soil or containers.

Early spring

Apply a light feed if needed and check emerging shoots for slug damage.

Late spring

Water during dry spells while growth is active; support stems only on very exposed sites.

Early summer

Leave fading flower heads for structure or remove them; allow the leaves to die back.

Late summer

Lift and divide congested clumps if necessary, keeping dormant bulbs out of wet soil.

• Plant in repeated groups through sunny borders to create a rhythm of purple spheres.
• Grow among catmint, hardy geraniums or salvia so their foliage conceals the allium's yellowing leaves.
• Use against clipped evergreen hedges for a clear contrast between rounded flowers and a dark background.
• Combine with ornamental grasses and later-flowering perennials, retaining the dried heads for summer structure.
• Plant in gravel gardens where drainage is good and the flower heads can rise above low planting.

Garden styles it suits: Architectural minimal, English country, Cottage garden, New perennial (prairie), Dry gravel garden and Pollinator garden.

Plant it with: Catmint, Hardy geranium, Perennial salvia, Lady's mantle, Peony and Feather reed grass.

Wildlife: Flowers attract bees and other pollinating insects. This sterile hybrid does not provide a useful seed crop for birds. Deer and rabbits usually leave it alone, though no plant is completely browsing-proof.

• Bulb rot in wet soil: improve drainage, avoid summer overwatering and discard soft or rotten bulbs.
• Slugs and snails on emerging leaves: inspect young growth and use barriers, hand collection or a locally approved control.
• Few flowers or small heads: provide full sun, let leaves die naturally and divide overcrowded bulbs; warm-winter climates may not provide enough chilling.
• Yellow leaves around flowering time: this is usually normal dormancy rather than disease; hide the foliage with nearby perennials instead of cutting it off early.

All parts, especially the bulbs, are toxic to cats, dogs and horses if eaten and can cause serious red-blood-cell damage and anaemia. It is not an edible onion; ingestion can also cause stomach upset in people. Keep bulbs away from children and pets, and seek veterinary advice promptly if an animal eats them.

• Star of Persia (Allium cristophii)

  Usually shorter, with a more open globe of distinctly star-shaped, metallic lilac flowers; 'Globemaster' has denser heads on taller stems.

• Giant ornamental onion (Allium giganteum)

  Usually taller, often reaching 4-5 ft (1.2-1.5 m), with smaller, tightly packed flower globes relative to its height.

• Purple Sensation ornamental onion (Allium hollandicum 'Purple Sensation')

  Has much smaller, generally darker purple flower heads and narrower leaves; it can also self-seed, unlike sterile 'Globemaster'.

Allium is the Latin word for garlic, while 'Globemaster' refers to the cultivar's large, globe-shaped flower heads.

Propagation. Separate offset bulbs after the leaves have died back and replant them in well-drained soil. Small offsets may take several years to reach flowering size. 'Globemaster' is a sterile hybrid and is not propagated reliably from seed.

Accepted botanical name

Allium

Sources: GBIF (CC BY 4.0). The care and design notes are LandscapeGPT's own.