Clematis are a large group of climbing plants that are very popular for clothing walls, fences, pergolas and arches to bring colour into the garden. There are over 350 different varieties and they come in many colours and sizes. Some bear single blooms, others are doubles. There are open flat flowers, dangling bells and upright tulip-shaped blooms. Some are as large as dinner plates.
Most clematis are deciduous, but some are evergreen, giving you interest all year round. With careful choices you could have clematis in flower almost all year round, as different varieties flower at different times.
How to Choose Which Clematis to Grow
With so many varieties on offer, you need to narrow down your options. First decide where in your garden you want to grow a clematis. Is it to cover an ugly wall or fence, to clothe an arch or pergola or do you want to grow one through a shrub?
Clematis grown through large shrub roses can complement each other beautifully. Some clematis, such as montana types, are vigorous and fast growing. They can reach 6-10m in the right conditions. Others are much shorter and can be grown in pots or hanging baskets. Some clematis like to be in full sun and others like part shade. All clematis prefer to have their roots shaded even if the rest of the plant is in full sun. Clematis in full shade will flower quite poorly.
After the ‘where’ decide on the ‘when’ – which time of year do you want it to flower? Winter to spring, late spring to early summer or late summer to autumn?
Thirdly choose your colour. Clematis are available in every colour except bright orange, most are in the red, pink, purple, blue and white range.
When choosing your plant, check the label information. This will tell you the height it will reach, if it likes sun or part shade and the essential group number.
Planting Clematis
Clematis need moisture-retentive soil, so before planting, dig a deep hole and work in plenty of compost. If planting against a fence or wall, position the hole 30-45cm from the base, or further out if there is an overhanging roof. Sprinkle mycorrhizal fungi (such as Rootgrow) into the hole to help plants establish well.
Large-flowered clematis should be planted deeply, with the top of the rootball about 10cm below the soil surface, encouraging new shoots from below ground and helping protect against clematis wilt.
Other types of clematis can be planted with the top of the rootball just below the soil surface, with strong canes added to guide stems to their supports and mulch applied to retain moisture. Clematis prefer shaded roots, so if there are no plants to provide cover, use tiles or pebbles. If growing through a shrub or tree, plant at least 1 metre away and train stems towards the trunk, avoiding dead stumps which can harbour diseases like honey fungus.
Smaller clematis, including some Group 3 types, are well suited to containers with a trellis or obelisk, using a pot at least 45cm wide and deep filled with soil-based compost such as John Innes No. 3, and finished with a mulch to keep roots cool.
Ongoing Care
Feed in spring with a potassium rich fertiliser around the base and mulch on top.
Clematis are thirsty plants and become stressed by drought. For the first few seasons they will need to be watered weekly. Once established you just need to water during dry spells. Clematis grown in a pot should be watered regularly.
Most clematis naturally twine around stems and supports, it is necessary to encourage this process and guide stems to spread out evenly. Take care because clematis stems are brittle. Group 3 clematis growing through roses will need very little tying in, as they will scramble naturally through the shrub.
Clematis Groups and Pruning Regimes
Clematis are grouped according to their flowering and pruning requirements.
Group 1 Clematis
Group 1 Clematis are winter to spring flowering varieties that bloom on old growth, such as Clematis armandii, C. cirrhosa, C. alpina and C. montana. They do not need pruning unless they become too large, though damaged stems can be removed after flowering. Many are evergreen, providing year-round coverage, and they tend to have smaller flowers than summer flowering types. They are often vigorous plants that can reach up to 10m and will require strong support.
Group 2 Clematis
Group 2 Clematis are large-flowered hybrids that bloom on the previous year’s growth. Without pruning, plants can become top heavy and produce a poorer display.
In February, trim back weak or damaged stems and cut others to just above the strongest, highest buds. They flower in spring and early summer, and after the first flush, stems can be cut back by half to encourage a second flowering in late summer to early autumn.
Group 3 Clematis
Group 3 Clematis are late-flowering varieties that bloom only on new growth, including C. viticella, C. texensis and tangutica types.
All should be cut back each February or March to just above a pair of buds about 30cm above the ground. These vigorous climbers are useful for growing through shrubs such as roses, as well as on obelisks or in pots.
Clematis Problems
Pests
Clematis can be attacked by the usual garden pests such as aphids, snails and earwigs. Try to remove pests by hand or live with what is a healthy garden ecosystem. Spraying with insect killer will kill the ladybirds and other good bugs too. After spraying, aphids will recolonise faster than their predators, making the problem even worse.
Mildew
This fungal disease looks like the leaves and buds are covered in white powder. It often occurs if the foliage is damp or humid but the roots are dry. Keep your plant well watered and water early in the morning. Make sure there is good air flow around your plant. Prune out and bin affected leaves and stems.
Clematis Wilt
This fungal disease causes plants to die suddenly and without apparent reason. Stems blacken and wilt quickly. If you suspect clematis wilt, check down the stems, as wilting may be a sign of a damaged stem. Keeping your plant healthy helps to prevent wilt.
Green Petal
This problem occurs as a result of flower buds emerging when it’s too cold. Pale or white-flowered cultivars are particularly prone to this problem. Normal flowers should be produced as the season progresses and temperatures rise.
Clematis Slime Flux
This is a bacterial infection in cuts or damaged stems. Treat in the same way as Clematis Wilt and don’t compost the diseased prunings.
Enjoy Clematis Throughout the Seasons
With their wide range of colours, flower shapes and flowering times, clematis are one of the most rewarding climbers for any garden. By choosing the right variety, planting it in the right place and providing a little ongoing care, you can enjoy a spectacular display year after year, whether covering a wall, climbing through a shrub or adding height to a container garden.
Continue your Gardening Journey
Need a little extra advice? Visit your local Tates of Sussex Garden Centre today, where our friendly knowledgeable, team will be happy to help you choose the right plants and offer expert guidance.
