Jackman’s Clematis

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Taxonomy

Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Order: Ranunculales
Family: Ranunculaceae
Genus: Clematis
Species: Clematis × jackmanii (hybrid origin)
Cultivar: ‘Jackmanii’

Common Names by Region

• Jackman’s Clematis
• Large-Flowered Purple Clematis
• Late Summer Clematis

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Description

Growth Habit

A vigorous, deciduous, climbing perennial vine that twines by leaf petioles. Typically reaches 8–12 feet in height when supported.

Leaves

Opposite, compound leaves with smooth margins. Medium to deep green. Leaflets ovate to elliptic, soft but sturdy.

Flowers

Large (4–6 inches across), star-shaped blooms with 4–8 pointed tepals. Rich violet to deep purple coloration. Central stamens creamy to pale yellow. Blooms heavily on new growth in mid- to late summer.

Petals (technically tepals) may fade slightly toward bluish tones in intense sun.

Seed Heads

After flowering, forms distinctive silvery, feathery seed clusters — a persistent ornamental feature.

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Known Range

Cultivated worldwide in temperate climates.
Hardy in USDA Zones 4–8.

Commonly planted across Pennsylvania and the northeastern United States.

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Care / Habitat

• Light: Full sun to partial shade (best flowering in 6+ hours of sun)
• Soil: Well-drained, moderately fertile soil
• Moisture: Even moisture preferred; avoid waterlogging
• Root Preference: “Head in the sun, feet in the shade” — roots benefit from mulch or companion ground cover

Requires structural support such as trellis, fence, arbor, or shrub.

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Propagation / Reproduction

• Semi-ripe cuttings
• Layering
• Grafting (historically common in nursery trade)

Seed propagation does not reliably produce true ‘Jackmanii’ offspring due to hybrid nature.

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Pests / Diseases / Threats

• Clematis wilt (fungal stem collapse)
• Aphids
• Slugs (young growth)
• Powdery mildew in stagnant air conditions

Proper airflow and deep planting reduce wilt risk.

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Maintenance / Management

Pruning Group 3 (Late-flowering)

• Cut back hard in late winter or early spring to 12–18 inches above ground.
• Blooms on current season’s growth.

Heavy annual pruning encourages vigorous flowering.

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Additional Notes

‘Jackmanii’ was introduced in 1862 by English nurseryman George Jackman and became one of the most widely planted clematis cultivars in the world.

Because many purple large-flowered hybrids resemble this cultivar, field identification without nursery tag confirmation should be noted as “Jackmanii-type large-flowered hybrid.”

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Field Notes (CF Observation)

Observed blooming in late summer in western Pennsylvania. Classic large star form, medium violet coloration, creamy filament center, and developing feathery seed heads consistent with Jackmanii-type hybrid characteristics.

Identification made by visual morphology and bloom timing. Cultivar confirmation would require original planting records.

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