Royal Horticultural Society

Cultivation notes

Clematis need moisture-retentive, but well-drained soil. The herbaceous species prefer full sun, but most climbers and shrub species will thrive in full sun or partial shade.

Keep the base of the plant and the roots cool and shaded by carefully positioning other plants, or put a layer of pebbles or flat stones at the base.

Planting

Plant large-flowered cultivars that bloom in May to June with the tops of their root balls 5-8cm (2–3in)  below the soil surface. This will encourage shoots to grow from below soil level and also helps the plant to recover if affected by clematis wilt.

Herbaceous and evergreen species such as Clematis armandii and C. cirrhosa should be planted with the crown at soil level.

Maintenance

• Each year, in late winter or early spring, apply a potassium-rich fertiliser (such as Vitax Q4 or rose fertiliser), according to the manufacturer’s instructions.
• Mulch immediately afterwards with organic matter such as well-rotted manure, leafmould or garden compost.
• Water regularly during periods of dry weather in the first few seasons after planting. Watering to soak the root zone requires at least the equivalent of four watering cans per square metre.

Container cultivation

Clematis make pretty container plants, especially if trained up an obelisk or small trellis. Choose cultivars such as C.‘Barbara Jackman’, C.‘Miss Bateman', or C.'Bee’s Jubilee’, which are smaller-growing.

Use containers that are at least 45cm (18in) deep and wide and use a soil-based potting compost such as John Innes No.2.

Make sure you water regularly during the growing season and apply a general-purpose liquid fertiliser monthly during spring and summer.

Replace the top 2.5-5cm (1–2in) layer of compost each spring with fresh potting compost.

Links

Container maintenance

Pruning and training

Plant positioning and training

• Grow clematis through, or over, trees and shrubs to extend their seasonal interest. Choose the clematis carefully, as vigorous types can be smothering.
• When used to cover walls, fences or pergolas, provide a form of support, such as trellis or mesh, for the clematis to twine around.
• Those clematis that are not true climbers (shrubby and herbaceous types) require tying in to their supports.

Initial pruning for newly planted clematis

• To avoid the development of a straggly single stem and to encourage branching lower down, cut back all newly planted clematis to 15-30cm (6–12in) from ground level in February or March, cutting just above a bud.
• Even if planting later in the spring, hard pruning is still advisable. Delay pruning of autumn-planted clematis until the following spring.
• Pinch out developing young shoots once or twice to promote further branching.

Pruning established clematis

Clematis has a reputation for being difficult to prune, but it isn’t, as long as you know when your clematis flowers, as pruning groups are based on flowering times. We have complete instructions in our clematis pruning profile.

Links

Clematis pruning

Propagation

Clematis can be propagated by double leaf bud cuttings taken from spring to late summer, or by layering from late winter to spring.

Species clematis can be propagated by seed.

• Ideally sow seeds fresh in the autumn and cover them with a fine layer of compost and grit.
• Keep the pots in a cold frame or unheated greenhouse, as they need a cold period to germinate well.
• They should germinate the following spring.

Links

Propagating climbers
Layering
Growing shrubs from seed

Cultivar Selection

Shady walls: C. alpina AGM, C. macropetala, C. montana, C. ‘Ernest Markham’ AGM, C. ‘Comtesse de Bouchaud’ AGM, C. ‘Perle d’Azur’, C. ‘Jackmanii’ AGM and all those in the Jackmanii Group, plus almost all the early-flowering deciduous species (flowering in April or May).

Sunny walls (west-facing is ideal): C. armandii, C. cirrhosa var. balearica, C. orientalis, C. tangutica, and most mid to late summer flowering, large-flowered cultivars including those in the Viticella Group.

Good clematis for pots include: C. ‘Barbara Jackman’, C. ‘Miss Bateman’ AGM, C. ‘Bee’s Jubilee’, C. alpina ‘White Columbine’ AGM and C. macropetala.

Links

AGM plants
RHS Plant Finder
RHS Plant Selector
RHS plant trials

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Clematis 'Avalanche'

Clematis 'Helsingborg'

Problems

If flowering is disappointing, apply sulphate of potash in late winter or early spring. Sometimes plants produce green flowers early in the season.

Pruned stems may fail to reshoot and ooze a sticky substance, this is known as slime flux.

Clematis may suffer from diseases such as clematis wilt and powdery mildew.

Clematis can be also attacked by pests such as aphids and capsid bugs. Flowers may be damaged by earwigs, and young shoots are vulnerable to slug and snail damage. 

Container-grown plants can suffer vine weevil larvae damage.

Links

Clematis wilt
Powdery mildew
Vine weevil
Slugs
Snails
Aphids
Capsid bug
Earwig
Clematis green flowers