Allium 'Globemaster', globemaster onion
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Bulbs

Allium 'Globemaster'

globemaster onion

Amaryllidaceae

Hybrid (parent species from Iran, Turkey, Central Asia)

At a Glance

TypeBulb
HabitUpright
FoliageDeciduous
Height30-36 inches (76-91 cm)
Width12-18 inches (30-46 cm)
Maturity3 years

Growing Zones

USDA Hardiness Zones

4 - 8
Zone 4
Zone 5
Zone 6
Zone 7
Zone 8
These zones indicate the coldest temperatures this plant can typically survive.
Frost Tolerancehardy

Key Features

Attracts Pollinators
Attracts Butterflies
Deer Resistant
Drought Tolerant
Fragrant (moderate)
Container Friendly
Maintenancelow

Overview

Allium Globemaster is a sterile hybrid bulbous perennial cultivar reaching 30-36 inches (76-91 cm) tall with a spread of 12-18 inches (30-46 cm). The cultivar is a cross between Allium macleanii and Allium christophii, combining large flower head size with tall, sturdy stems. Spherical umbels measure 6-8 inches (15-20 cm) in diameter, occasionally reaching 10 inches (25 cm), composed of hundreds of individual deep violet to pinkish-purple star-shaped florets, each approximately 0.25 inches (6 mm) across. Hollow, sturdy stems (scapes) remain upright without staking under normal conditions. Blue-green strap-like basal leaves emerge in spring, measuring 12-18 inches (30-45 cm) long, and die back before or during flowering; yellowing and declining foliage while flowers are at peak bloom is a consistent and unavoidable feature of this cultivar. Because flowers are sterile, they last 4-5 weeks, significantly longer than seed-producing alliums that typically bloom 2-3 weeks. Dried flower heads retain structural form through fall and winter, turning silvery-tan rather than becoming loose and open as in seed-producing species. Bulb clumps increase slowly by offsets; flowering-size offsets can be separated every 6-8 years.

Native Range

Not found in wild habitats. This cultivar is a hybrid developed in Dutch nurseries through crossing Allium macleanii (native to Iran and Turkmenistan) and Allium christophii (native to Iran, Turkey, and Central Asia).

Suggested Uses

Planted in perennial borders at 12-15 inch (30-38 cm) spacing, in groups of 3-7 bulbs. The spherical flower form provides vertical contrast to mounding or spreading perennials. Positioning behind low-growing perennials such as catmint or hardy geraniums that expand after bloom conceals yellowing allium foliage. Dying foliage during peak bloom may be unacceptable in formal settings; better suited to naturalistic or cottage-style plantings.

How to Identify

Identified by very large, perfectly spherical flower heads, 6-8 inches (15-20 cm) in diameter, composed of hundreds of deep violet to pinkish-purple star-shaped florets densely packed on 30-36 inch (76-91 cm) hollow stems. Distinguished from other large-flowered alliums by sterile flowers that do not set seed, giving a bloom period of 4-5 weeks versus 2-3 weeks for seed-producing species. Blue-green strap-like basal leaves 12-18 inches (30-45 cm) long yellow and die back during or before bloom. All parts emit an onion odor when crushed. Dried flower heads remain structurally intact through fall and winter, turning silvery-tan.

Appearance

Size & Dimensions

Height2'6" - 3'
Width/Spread1' - 1'6"

Reaches mature size in approximately 3 years

Colors

Flower Colors

purple
pink

Foliage Colors

blue green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~5 weeks
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SpringSummer
Late May through June in zones 5-7; extending into early July in cooler climates (zones 4-5). In zones 7-8, flowering typically begins in early May and finishes by mid-June. Individual flower heads last 4-5 weeks due to sterility; seed-producing allium species bloom for 2-3 weeks by comparison. Heat accelerates bloom timing; cool overcast conditions during bloom extend the display. Flowers transition from deep violet to silvery-purple tones as they age.

Detailed Descriptions

Flower Description

Deep violet to pinkish-purple star-shaped florets in spherical umbels

Foliage Description

Blue-green strap-like basal leaves, 12-18 inches long, dying back before or during flowering

Growing Conditions

Sun Requirements

Full Sun
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.5 - 7.5(Neutral)
357912
Soil Types
loamsandchalk
Drainage
well drained

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

2-3 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Requires well-drained soil; bulbs rot in heavy clay or areas with standing water, particularly during winter dormancy from October through March. Plant bulbs 6-8 inches (15-20 cm) deep in fall — September to October in zones 4-6, October to November in zones 7-8. Water regularly during active growth in spring (March through May), providing 1 inch (2.5 cm) weekly in absence of rain. Reduce watering significantly as foliage begins yellowing in June; bulbs prefer dry conditions during summer dormancy from July through September. In zones 4-5, apply 3-4 inches (8-10 cm) of mulch over the planting area after ground freezes to moderate temperature fluctuations. Foliage yellows and collapses concurrent with or just before peak bloom; this is a consistent trait of the cultivar.

Pruning

Allow foliage to yellow and die back naturally; do not remove green leaves even though they become unsightly during bloom, as leaves are storing energy in the bulb. Remove foliage only after it turns completely brown, typically late June to July. Cut flower stems at the base in July-August for a tidy appearance, or leave dried heads standing through fall and winter. Divide bulb clumps in fall (September-October) every 6-8 years when clumps become crowded and flower size diminishes.

Pruning Schedule

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Maintenance Level

low

Container Growing

✓ Suitable for container growing

Minimum container size: 5 gallons

⚠️ Toxicity Warning

Toxic to pets

Planting Guide

Planting Methods & Timing

Planting Method

transplant