What's wrong with my clematis?

Introduction

Except for a few large-flowered types being prone to wilt, clematis do not suffer from pests and diseases any more than other garden plants, so the methods of prevention and control are the same too.

Clematis wilt

This is a fungal disease that can affect a healthy mature plant in early summer but normally affects a specimen already under stress from other causes, such as lack of water at the roots. Buds and foliage suddenly droop on one or more stems and if this condition remains an hour after a thorough soaking (two gallons of water over root area) then it is likely to be clematis wilt. Prune affected stems, and the complete plant if necessary, to ground level, and dispose of removed material without composting it.

Apply a clematis or rose fertiliser and keep it well watered; growth often restarts within a few weeks. Plants that fail again are best got rid of, but the soil is not affected, and another clematis can be safely planted in its place.

Powdery mildew

This is an unsightly whitish powder affecting both foliage and flowers, but it is seldom severe enough to harm the plant. Clematis with C. texensis in their bloodline suffer more than most types. When the root area of the plant is subject to alternate soaking and drying out completely, the resultant stress leaves the plant open to an attack by this fungal disease. Ensuring plenty of airflow through and around the plants helps prevent mildew and monthly spraying of the plant throughout the growing season with a rose fungicide will keep any attack under control.

Pest damage

Slugs and snails will eat new shoots and rasp off the outer skin of stems. They are great climbers. Look carefully at your trellises, especially near the top. New clematis growth emerging at soil level will tempt mice as well as snails and slugs. In the UK most of the texensis and integrifolia types will push up new green shoots from under the ground, making a lovely breakfast for pests. How you deal with them is up to you. Most are nocturnal so occasionally go out with a torch and container on a damp evening and pick them off your plants or paths.

Buds and flowers are a tempting morsel for earwigs. You will never get rid of them all – that would be tragic for the species and those that rely on them for food – but you can assuage your frustration on some by putting a pot upside down with some newspaper scrunched up inside it, placed on a bamboo cane that is stuck in the ground near your clematis. In the morning tap the earwigs out elsewhere or dispose of them. Rabbits and deer are partial to most things, but you will need a 3m high fence to keep them all out!

Lack of adequate feeding

Large-flowered clematis are gross feeders, like roses and dahlias. High-potash fertiliser, as granules or in liquid form, applied in the spring and again after a few months, will help ripen the stems and give the flowers good colour. New plantings should be watered regularly for the first year. Small-flowered clematis do not need as much; a spring feed of blood, fish and bone and an autumn feed of bone meal is quite sufficient. Containerised clematis will require liquid fertiliser right through the growing season.

Planted in the wrong place

Plant a short distance away from walls and trees, and train the stems up a cane to your supports. Walls and trees will draw all moisture from the nearby soil like blotting paper. There may also be some rain-shadow from overhanging roofs and branches. Plant clematis on the north or rainy side of trees and shrubs. When planting two together make sure they require the same type of pruning.

To obtain bushy plants, pinch out the growing tips of shoots that are 30cm long, thus doubling the number of stems and making the plant more compact.

Not thriving in a container

Clematis in containers have very little compost to live in and therefore require extra attention. They must have good drainage as they will not thrive if sitting in water. Lift containers off the ground with pot feet to allow drainage. To help prevent containerised roots in plastic pots from becoming too hot or too cold, line the inside with insulating material before planting; bubble wrap or similar is fine. For continuous use, containers should be at least 46cm wide and deep, and using compost suitable for containers is also very important. Water regularly, sometimes twice daily if south-facing and located in a sheltered position.

Lack of flowers

Pruning clematis in the wrong season will mean you may have removed the material that was going to bear the blooms, so check your plant label for the correct time to prune. Another cause of lack of blooms is overfeeding of small-flowered clematis, which causes abundant foliage but poor blooming. This overfeeding can also make the clematis soft and more liable to pest and insect damage.