The World of Clematis

Clematis is one of my favourite climbing plants. They are renowned for their huge variety of flowers and leaves. One of the first types of Clematis to be introduced into England was Clematis Viticella, the light purple bell-shaped flower. There are now lots of different species of C Viticella, but the first original was introduced into this country from Spain in 1569. This was the start of the breeding program through hybridization. From 1596, there were more varieties introduced, which was the start of the Clematis foundation.

There are evergreen (leaves which stop on all year round) and deciduous (leaves which fall off during autumn/winter) types. The common one is the deciduous type, as the flowers are much bigger and brighter, with such an array of colours. All types are ideal for covering that unsightly fence or wall, or growing up specially designed archways to provide a focal point or cover. Some groups grow fast, others slow, depending on the species grown.

These are the different groups and what they mean:

Group One: Early flowering cultivars. The flowers are produced on the previous year's growth in winter/early spring. They are usually fully hardy, but the flowers are generally small and look more delicate than some of the other groups. They do prefer a sunny site with a little shelter from cold prevailing winds.

Next are some examples:

C alpina (Alpine Clematis) and varieties: These are usually open-bell-shaped flowers, mainly glorious blue and purplish flowers. The majority of them are deciduous.

C macropetala (Downy Clematis) and varieties: These again are usually open-bell-shaped flowers. They are deciduous with a different colour of flower according to the type. After flowering, there are silvery coloured seed heads.

C montana and varieties: A fast and vigorous climber which is ideal for covering an eye-sore quickly. They are deciduous and the flowers come in a range of colours, again depending on the type.

Group Two: Early to mid-season large-flowered cultivars. The flowers appear in late spring or early summer on side-shoots which grow from the previous year's growth. They can flower a second time in mid to late summer, depending on the weather situation. Another advantage is they're fully hardy, except the tips may get damaged in frost.

Examples of ideal species

There are a lot of different species in this group, so here are some of my favourites:

C caraby - This is a lovely mid to dark pink single flower, which is one of the early types in Group two. The flowers do fade in full sun, but while it is in flower, it stands out and makes a lovely show. There are different varieties, which reach various heights and spreads.

C florida - There are several types of this species which are deciduous or semi-evergreen, depending on variety. They bear single white, creamy flowers with different-coloured stamens. They flower in late spring/early summer, and like a sheltered position safe from heavy frosts. They can reach an estimated height of 4 m (12 ft) and a spread of 1 m (3 ft).

C Lasurstern - A large single-flowered variety, bearing lovely blue flowers, which is fairly early in season. It is frost-hardy, reaching an estimated height of 2.5 m (8 ft) and a spread of 1 m (3 ft).

Group Three: Late, large flowering species. These have flowers in summer to early autumn, which flower on the current year's growth. They are fully hardy and deciduous.

Again, there are such a lot of species, I will name three of my favourite ones:

'C Bill MacKenzie' - This is a fast, vigorous climber, bearing late (mid summer to early autumn) bell-shaped flowers. These are bright yellow with red anthers. After flowering there are fluffy silvery coloured seed heads, which stay on throughout the winter. This particular variety is thought to be a cross between C orientalis and C tangutica. It can reach a height of 7 m (22 ft) and a spread of 2-3 m (6-10 ft). It is fully hardy and a tough old plant.

C 'Duchess of Albany' - This is a late flowering climber (mid summer to late autumn), producing tulip-shaped dark pink flowers. It is deciduous and fully hardy, reaching a height of approximately 2.5 m (8 ft) with a spread of 1.5 m (5ft). This is an ideal slow-growing climber.

C heracleifolia Wyevale - This one looks quite unusual, which is why it appeals to me. It has blue clustered flowers, with leaves spaced well apart. It does require more support due to its growing habit, but I think it is worth it just to see the glorious blue flowers. It grows an estimated height of 75 cm (30 in) and a spread of 1 m (3 ft). As you can see by the sizes, it remains small, making it ideal for a large pot or container.

Other Group Three Species: Late flowering species and small flowering cultivars - these have the same description as the normal Group Three, except the flowers are much smaller.

Herbaceous species and cultivars - These again bear flowers on the current year's shoots during mid-summer to late autumn. They are ideal for mixed perennial borders, are fully hardy but do not like water-logged soils as this causes the roots to rot (More about this condition in the Pests and Diseases section).

Positions of Growing & Planting

I feel the most important factor when growing Clematis is the position in which they are being grown. Clematis prefer sun or partial shade, depending on variety. It is important that they are grown in a well-drained soil and the roots and base are in shade. If natural shade at the base is not available, then covering with rocks or stones will do the trick. Do not put stones or anything else right up against the stems, as it will cause rotting.

It is usually best to plant in spring or autumn when the ground isn't frozen or waterlogged. I say spring or autumn as it is cooler then, and the newly planted Clematis will not need as much water. However, it is possible to plant in summer if you choose a cool day and keep a check on watering it.

When planting into the ground, you need to dig a hole twice the width of the pot, ensuring the surface of the root ball is at least 3 inches (7.5 cm) below the level of the soil. Mix in plenty of compost and grit before planting, scattering grit around the base of the stem afterwards to discourage slugs and snails. Remember to water in well, and feed with a balanced fertiliser during the growing season.

When planting deciduous types cut back the top growth to 12 inches (30 cm) from ground level to a healthy set of shoots, tying these in so you can train it up a wall, fence etc. If it's in full flower then leave alone when planting. By doing the procedure of trimming when planting, it helps with new healthy growth and shape.

You can plant Clematis in a container as long as it's fairly large. The container you choose must be a minimum of 18 inches (45 cm) by 12 - 18 inches wide (30 - 45 cm). All I can say is 'the bigger, the better'! There is such a range of containers to choose from today; terracotta, plastic, wood, or stone in many different colours and shapes. The most important thing to look for is drainage holes. Make sure adequate holes are in the bottom to avoid water-logging. I would advise putting the container on pot feet or bricks to ensure free drainage.

The type of compost to use in the container must be a well-draining one. I wouldn't recommend multi-purpose, as this often dries up quickly. The best one is John Innes No 3, which is loam based. It has the advantage of weighing heavier than multi-purpose composts, protecting the pot from falling over in strong winds, as well as not drying out quickly. I would also recommend adding grit into the compost as it helps with drainage, also broken crocks or stones at the bottom of the pot will help, too.

When choosing a Clematis for your pot, go for the less vigorous type which won't fill the pot with its root system quickly, resulting in lots of watering. There are many varieties to choose from, but remember to grow it up against some kind of support such as trellis, tying in any new shoots on a weekly basis.

Check for watering on a daily basis, especially during warm days, feeding every fortnight with a feed containing equal amounts of nitrogen and potash. You can buy Clematis feed, which contains all of the essential nutrients needed for healthy growth.

You can even grow Clematis in your greenhouse or conservatory in pots. They will grow quicker and require more attention than those grown outdoors, but if you have a large enough area inside, then give it a go. The flowering period will probably be shorter, but at least you won't get the flower damage caused by harsh weathers.

Pruning Clematis

If, when planting you could not prune because of flowering, then it should be done the following February/March. Remove the growth from each stem above the first set of live stems. Make a clean cut, pinching out the tops of new growth as it matures. This will encourage the plant to bush and spread into the desired shape. The only ones you don't do this to are the herbaceous types, which will die off like any other herbaceous plant in autumn to late February. If necessary, remove or prune the dead stems to encourage new growth from soil level.

As for established Clematis (more than one year old after planting), this is where the group numbers I explained earlier will be useful:

Group one Clematis require no pruning. You can remove any dead or unsightly stems, but if you do need to prune harder then the best time is immediately after they have flowered. However, it is a 50–50 chance whether they will survive or not. Only prune lightly, even if it means taking a few seasons to get the shape you require.

Group two Clematis require any dead or weak stems to be pruned out around February/March. It is best to start at the top and work down, pruning any weak stems to just above a healthy set of leaf buds. If you hard-prune it then you will not get any early flowers. When the flowers have finished, cut back the flowering shoots to encourage healthy growth. If you do want to prune it back hard then this will be the time to do it. I would recommend that you prune gradually over the seasons to avoid loss of the Clematis.

Group three Clematis are a little more tricky. These are the late flowering varieties which flower on the current seasons shoots. The best time for pruning is again, February/March time. Work from the bottom upwards, working your way up each stem to the first pair of healthy buds. Remove anything else above this, treating all the stems the same way. It sounds a little vicious, I know, but it is the best way to get healthy and wonderful flowers for the current season.

Good luck, and remember: if you need any further advice, don't be afraid to ask me!

Pests and Diseases

The first disease that always comes to mind when talking about Clematis, is the dreaded 'Clematis Wilt'. It is caused by a sudden fungus which causes the plant to suddenly wilt and eventually collapse, starting with the upper parts of the plant. Occasionally, the Clematis can be saved by cutting back to ground level completely, burning any infected material in an appropriate incinerator.
Unfortunately, there is currently no chemical available on the market to deal with this wilt. If the Clematis does not come back after cutting it hard back, I would recommend that you do not plant a Clematis in the same area. You could dig the old soil out, replacing it with new before re-planting. However, the first option would be my recommended one. There are other diseases which have the same symptoms as 'Clematis Wilt', so be certain it is definitely that before doing anything drastic.

'Powdery Mildew' is a fungus which Clematis are prone to, and some varieties are worse than others. It is usually caused when the plant is put under stress, e.g. lack of water or too much. It only affects the leaves, and can be treated with a suitable fungicide.

'Aphid attacks' are quite common on Clematis. They is usually caused by greenfly and blackfly which suck the sap out of the leaves, usually from the new shoots, which causes the plant to stop growing and basically look sick. The best option is to plant nearby plants which attract ladybirds, which will eat the aphids. If infestations are bad, then spray with an insecticide will help.

Caterpillars can cause damage to the new growth on Clematis, mainly in spring. The best way is to hand-pick them off during spring time, but if infestations are bad, a suitable pesticide can be used if instructions are followed carefully.

Leaf Miner causes a light brownish line, usually on top of the leaves, which looks a bit unsightly if left. It is best to remove these leaves as soon as possible, because it could get out of hand. There are suitable insecticides on the market to deal with bad infestations, but it is usually difficult to eradicate when they have taken hold. Remember to burn any affected leaves you take off, don't compost them, as the larvae could spread.

The most common problem we used to have at the garden centre were rabbits biting the stems off, usually around the base part, which meant the Clematis wasn't much good afterwards. If this does happen, then cut away the dead top growth to see if it re-shoots from soil level again. It may take some time but is worth persevering.

Slugs and snails can be a real pain, eating your juicy young leaves, especially at night time. The best thing is to put a layer of grit around the base of the Clematis to deter them.

Vine Weevil is a gardener's worst nightmare. The adult insects look beetle-like, while the larvae looks like a white caterpillar type bug which lives in the soil, eating away at the roots. They cause the whole plant to collapse and die, and they could spread to your garden or pots. However, never fear because there are getting more controls on the market now such as nematodes or a vine weevil chemical, both of which you mix in a watering can and water in. Nematodes are the best to use. Although expensive, they help better than the average chemicals.

Whitefly is usually only a problem in conservatories or greenhouses; during warm, sunny spells they can be a nuisance on outdoor plants but don't usually do any serious harm. There are suitable insecticides which can be used, but a useful tip I found is to plant Marigolds around the affected plants which deters Whitefly because of the smell and strong orangey colour.

Wilting can also be the cause of over-watering or under-watering, so check carefully to make sure the soil is not too wet or too dry. A sign that a Clematis is not getting enough water is that its leaves go dry and crispy. During warm weather, check every day for watering.

Read also: Alternative Pest Control for the Garden.

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