Description
Clematis ‘Jackmanii’ – late large-flowered clematis
Botanical name: Clematis ‘Jackmanii’
Common names: Jackman’s clematis
Family: Ranunculaceae (buttercup family)
Plant type: Deciduous climber
Habit: Vigorous, twining/scrambling
Pot size: As supplied
Eventual size: Approx. 3–4m tall × 1m spread
Foliage: Divided green leaves; deciduous
Flowers: Masses of velvety deep purple flowers, mid to late summer (July–September)
Scent: Not scented
Aspect / light: Full sun to partial shade, with the roots kept cool and shaded
Soil: Fertile, moist but well-drained; any pH
Hardiness: RHS H6 (hardy, to about −20°C); USDA zones 4–9
Exposure: Sheltered or exposed
Native range: Garden hybrid (first raised in the 1860s)
Toxicity / pet & child safety: Toxic if eaten and the sap can irritate skin — harmful to people and pets; wear gloves when pruning
Clematis ‘Jackmanii’ is a classic late large-flowered clematis with masses of velvety deep purple blooms from mid to late summer. Vigorous and reliable, it is superb scrambling over walls, fences and obelisks.
GardenAdvice notes
The original and most famous large-flowered clematis, ‘Jackmanii’ has been a garden favourite since the 1860s for good reason: it is vigorous, hardy, reliable and smothers itself in rich purple flowers through the second half of summer. It belongs to the late-flowering group (pruning Group 3), so it flowers on the current year’s growth and is easy to prune.
Growing & planting
Plant with the crown about 5–8cm below soil level (deeper than most plants, to help it recover from clematis wilt) in fertile, moist but well-drained soil. Give the top growth sun or light shade but keep the roots cool and shaded, with a slab, low planting or mulch over the root area. Provide a support such as a trellis, obelisk or host shrub to scramble through.
Care & maintenance
As a Group 3 clematis, prune hard each year in late winter or early spring, cutting all stems back to a pair of strong buds about 20–30cm above the ground — this keeps it flowering low down rather than in a tangle at the top. Water well in dry spells, especially while establishing, and feed and mulch in spring. Keep the roots cool and moist.
Propagation
- Layering: Peg down a stem into the soil in spring to root, then detach the following year — the easiest method.
- Cuttings: Take internodal semi-ripe cuttings in early summer.
Pests & diseases
‘Jackmanii’ is more resistant to clematis wilt than many large-flowered types, but wilt can still cause sudden collapse of a stem — cut affected growth back to healthy tissue and it usually recovers. Aphids, slugs on new growth and earwigs can occasionally be a nuisance.
Uses in the garden
Superb for clothing walls, fences, trellis, arches, pergolas and obelisks, and for scrambling attractively through large shrubs and roses to extend their season.
Wildlife value
The nectar-rich flowers attract bees and other pollinating insects through late summer.
Toxicity & safety
Clematis is toxic if eaten and the sap can irritate skin, making it harmful to people and pets. Wear gloves when pruning and site it away from where pets might chew the stems.
GardenAdvice tip
The secret to a well-clothed ‘Jackmanii’ is that hard late-winter prune — cut it right down to about 30cm every year and it flowers freely from low down, instead of becoming a bare tangle with flowers only at the top. And remember the old clematis rule: keep its head in the sun but its roots cool and shaded, with a slab or low planting over the roots.
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