Best Tips For Growing Large Flowered Clematis

Follow our hints and tips for spectacular summer colour on an obelisk

These clematis are hybrids bred to produce large flowers over a short period of time, typically around June. They often produce a second flush of flowers in early autumn if pruned back after flowering; if the first flush are double the second are usually just single smaller flowers. They don’t usually grow too tall; about 180 – 300cm (6 – 10’); although there are smaller varieties suitable for containers.

Clematis at Lakeland Horticultural Society Holehird Gardens

Planting

• Plant in spring or summer.
• Choose the correct position for your plant; some of the dark reds and blues and the very pale shades will bleach in strong sunlight so a semi-shaded spot would be ideal. Avoid the plant being in full sun in the heat of the day.
• Make sure they have something to climb over or up; wall, fence, pergola, arch, obelisk or through other shrubs or small trees. They look fantastic growing up an obelisk in an herbaceous border; where there is the added bonus of the other plants shading the roots and keeping them cool.
• Prepare the hole by digging it at least twice as large as the pot the plant is already in.
• Enrich with some well-rotted farmyard manure or good quality peat-free compost. Clematis like nice rich, moisture-retentive well-draining soil with a neutral pH of about 6.5.
• Add a handful of blood, fish and bone to the planting hole.
• Soak the plant before planting.
• Ease gently from the pot; don’t pull on the actual plant. Turn the plant upside-down and tap the rim of the pot to release the plant.
• Plant about 10cm (4”) deeper than it is in the pot; this will encourage more stems to form from the base.
• If planting against a wall plant at least 45 – 60cm (18 – 24”) away from the base of the wall otherwise it may be in the rain-shadow and not receive enough water. Angle the canes towards the wall the allow the plant to reach the supports.
• Place trellis or horizontal wires on the wall or fence to support the plant.
• They need their roots kept cool so after planting, water well and mulch with well-rotted farmyard manure, decorative stones or chipped bark.
• If planting in a container make sure it is at least 45cm (18”) in diameter and depth; and use a loam based compost, such as John Innes No 3. Add some slow-release balanced fertiliser.
• If planting in a container plant up some smaller containers and place around the clematis so that the sun doesn’t hit the side of its pot.
• If growing in a container provide an obelisk or a wigwam of canes or rustic poles for the plant to scramble up.

Clematis 'Kingfisher' and 'Zara'

Aftercare

• Prune in early spring; late February to early March. Take it down to just above a pair of buds around 20 – 30cm (8 – 12”) above the soil surface. Pruning in spring will encourage the plant to produce more stems from ground level, giving you a bushier plant, which is particularly important with a new plant. If you don’t prune you will end up with a few sparse bare stems and flowers way up at the top of the plant.
• After the first flush of flowers give it a light prune; just below the faded blooms and above a pair of buds. This encourages a second flush of flowers in late summer/early autumn.
• With an established plant take out any dead or weak stems to avoid over-congestion, which could lead to mildew. You are better off with fewer strong stems as they will produce larger flowers than a lot of weaker ones.
• Tie in the stems as they grow to give good cover over your wall or fence.
• Make sure it is kept well-watered; a good soak a couple of times a week is better than a little every day. Be especially vigilant in summer as a plant with a lot of foliage will lose a lot of water over the course of a hot day.
• Feed established plants with a rose fertiliser or dedicated clematis fertiliser in spring, water well and mulch.
• If growing in a container feed with a balanced fertiliser in early spring and as soon as the first buds have formed feed weekly with a high potash fertiliser, such as Tomorite, which will encourage the formation of more buds.

Clematis 'Bijou' and 'Bernadine'

Problems

• Slugs; protect young growth in spring from slug damage. If growing up a stone wall which has a lot of crevices you will have to be on slug alert throughout the growing season.
• Wilt; this is a fungal disease to which the large flowered clematis are particularly prone. The foliage and flowers will suddenly droop even though the plant is well watered. Cut it off just above soil level and place some clean, fresh compost over the plant, it should throw up new shoots from the base. The good news is that once the plant has had wilt it is unlikely to contract it again; so don’t dig the plant up give it a chance to re-grow. Put the foliage onto the bonfire or into the grey bin, don’t put it on the compost heap as this will only incubate the fungus.
• Mildew is a problem caused by the plant becoming too dry and a lack of air circulation. Make sure that it is kept well watered and that the stems don’t become too congested. If you spot the symptoms early and there is only a couple of spots, spray with a fungicide to prevent if spreading. If the fungus is widespread cut the plant back to a healthy pair of buds near the base and it should flower again in late summer.
• Frost can be a problem if new growth has emerged soon after pruning in late February, so keep an eye on the weather and cover with horticultural fleece at night if there is a threat.

Clematis 'Arctic Queen'

Varieties

• ‘Arctic Queen’ is the best double white, reaching a height of 150 – 180cm (6 – 8’). Suitable for a large container.
• The ‘Boulevard’ series grow to a height of about 90 – 120cm (3 – 4’) and are suitable for growing in containers. Try ‘Picardy’ a lovely deep velvety burgundy red or ‘Cezanne’ a bright lilac/blue.
• ‘Crystal Fountain’ is one of the best purple/blue doubles, only reaching a height of 150 – 180cm (5 – 6’), so is suitable for containers or growing up an obelisk in the herbaceous border.
• ‘Samaritan Jo’ has lovely white petals with a dark purple rim; it fades easily so needs a semi-shady position. It only reaches a height of 120 – 150cm (4 – 5’) so is suitable for a container.
• ‘Vienetta’ has really unusual double flowers; large outer petals of white with pale green tips, then a ring of smaller purple petals and finally a central boss of lime green petals which open up to be lilac. Again it is ideal for growing in a tub or up an obelisk.

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