Clematis × jackmanii
This classic clematis is the historic large‑flowered hybrid widely grown under the clone ‘Jackmanii’. It is valued for masses of velvety, violet purple flowers on new growth. It performs best in full sun with the root zone kept cool and evenly moist. It suits most temperate parts of North America where summers are not extreme. Train on a sturdy trellis or fence for the best display. Prune in late winter to encourage vigorous new shoots and abundant bloom.
At‑a‑glance
- Group/Class: Late large‑flowered clematis; Pruning Group 3
- Height × spread: 7–10 ft × 3–6 ft (2.1–3.0 m × 0.9–1.8 m)
- Bloom window: July to September
- Color & flower form: Deep violet purple single flowers, 5–7 in (12–18 cm) across
- Fragrance: 0 none
- USDA hardiness: zones 4 to 8
- Breeder / Year / Origin: George Jackman, 1862, UK
- Awards/registration: RHS Award of Garden Merit
- Pet safety: avoid
How it differs
- Blooms on current season wood while many early clematis flower on old wood
- Richer violet purple color than typical pale large‑flowered hybrids
- Moderate height compared with very vigorous ramblers
- Handles colder winters better than many large‑flowered forms
Strengths
- Profuse mid to late summer bloom on new growth
- Tolerates full sun with shaded roots
- Reliable in zones 4 to 8 when sited and pruned well
Care in one minute
- Site: full sun to part shade; shade the crown and roots with mulch or low perennials; good air flow.
- Soil: fertile, moisture‑retentive but well‑drained; neutral to slightly alkaline pH.
- Water: keep evenly moist through summer; do not let the root zone bake.
- Feeding: apply a low‑nitrogen, slow‑release fertilizer in spring; repeat light feeds during growth.
- Pruning: Group 3; cut back to strong buds 8–12 in above ground in late winter.
- Overwintering: mulch the root zone in cold climates to buffer freeze–thaw.
Watch‑outs
- Susceptible to clematis wilt in some gardens
- Needs support; stems can break if untied in wind
- Root zone should not dry out in summer heat
Best uses (tags)
borders, arbors, trellises, containers, pollinators
Provenance note
Raised from crosses among *C. lanuginosa* and *C. viticella* by George Jackman in England; introduction year reported as 1862 to 1863.
References
- Missouri Botanical Garden – Plant Finder: Clematis ‘Jackmanii’
- RHS – Clematis: pruning groups
- NC State Extension – Clematis × jackmanii
Written by: Your Flowers Guide editorial team
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