The challenges of growing clematis

Clematis are climbing beauties, never more so than in late summer, but they are prone to a disease called clematis wilt. Pursuing beauty, I am prone to a related disease, one called clematis-wish. It afflicts me at this time of year. I forget my previous failures and every August, I come back for more.

Clematis wilt is usually related to dry weather: most of its supposed casualties have merely become too dry and need immediate soaking with cans of water. Conversely, clematis-wish is most acute in cool, wet summers, just like the one British gardeners are enjoying. Flowerbeds are full and flowering but it is too early to plant bulbs and too late to do anything about gaps in the general picture. Clematis are the icing on a fully baked flowerbed: while surveying the garden I have been applying it in my mind’s eye. I read the lists, fall for their pictures and then go out and buy what I believe, this time, I can please.

The smaller your garden, the higher the chance that you will give your wishes the attention they appreciate. In my bigger garden they must take whatever they happen to get. My biggest success is with herbaceous clematis. I enjoy the scented mid-blue flowers on the lovely Cassandra, to my eye the best of the upright freestanding clematis for a border. It is about 3ft high and very robust, but it does not like to be crowded by strong neighbours.

On a different scale of strength and spread, I especially recommend the vigorous Clematis jouiniana, which exemplifies a truth about the entire family. Clematis are listed as climbers, but they do not cling and climb of their own accord. They have to be given wire netting against a wall if they are to go up it on their own. In the wild they use other plants as supports or just grow flat along the ground. Jouiniana will grow up a wall if supported on wires, but it is far better when allowed to fall forwards, even on to bare ground. In winter the dead, drab stems should be cut away, like the stems on herbaceous geraniums.

From September onwards, Clematis jouiniana will have given a profuse carpet of pale lavender-white little flowers like letter Xs. I have seen it grown flat as a cover against weeds on large areas of well-watered soil but I have not fully succeeded in growing it flat in the dry gaps between my avenues of tall pear trees. Clematis hope springs eternal, so I am still trying. On a nearby yew hedge, jouiniana is superb, covering itself in flower every year.

Best of all, I never lose it. Elsewhere, I plant clematis to run up beside other plants on walls, especially roses, but they do not often last longer than a decade. My successes here are all with clematis of the viticella group, especially the green and white-flowered alba luxurians and the lovely sky blue Emilia Plater, recommended and kindly sent by an FT reader. Plant a viticella clematis about 3ft away from the main stem and roots of a mature shrub and then point its supporting cane at an angle towards the shrub’s lower branches.

Last year’s dry summer did clematis in these positions no favours, but this year’s cool weather has been ideal for their re-establishment. The pruning of them is very simple: cut them down to about 6in from the ground in late winter and throw the top growth away. The supporting shrub then flowers, a spring forsythia or viburnum being ideal, and the viticella climbs back up it afterwards. Then you have two sequential shows of flower in one space.

Smaller gardens must use all available levels and this cloaking with clematis is one of the best uses. It is the sort of hope that late summer encourages, a time when you can work out how many of these clematis you can include for next year.

Two of the best sources for clematis by mail order in the UK are Taylors Clematis at Sutton near Doncaster and Thorncroft Clematis near Tewkesbury. Taylors is currently running special offers at £10 a plant, some discounted by nearly 40 per cent, among which have been some good viticella varieties.

The master grower and breeder of clematis is Raymond Evison on Guernsey, whose nursery also supplies by mail order. He provokes acute clematis-wish by writing in his handbook that “marvellous evergreen host plants for clematis include ceanothus, pyracantha and Garrya elliptica”, that shrub with grey-green catkins in winter. Their leaves, he well observes, have a very different shape and texture to a clematis’s, which will sprawl over them.

I read the lists, fall for their pictures and then go out and buy what I believe, this time, I can please

I find it hard to imagine a happy clematis in the dried-out ground around a ceanothus, but in damp shade I have a garrya, which is recovering from last winter’s frosting. Acting on clematis-wish, I have just bought one of Evison’s suggestions, his pale ice-blue Tranquilité, a fine companion for the garrya’s dark green leaves. He also recommends his dark rose-red Rosemoor and his recently released white, Tsukiko.

Frequent advice is to plant a tall clematis beside a newly planted climbing rose. I have passed this tip on and acted on it myself, but I do not find that the clematis in the combo is very long-lived. My favourite is still the tall blue Perle d’Azur, one which bears rounded flowers with rose-pink bars at their centres when they first open. In one season it will race up to the top of a medium-high climbing rose. I recommend it but after the recent dry summers and 10 years of life with apricot rose Lady Hillingdon, it has lost its impetus.

Water, regularly given, is crucial for getting the best from clematis, especially when planted in a combo, and so is a balanced plant food, Phostrogen being my favourite, applied in water from April onwards. An early start to the feeding season makes a big difference.

My current clematis-wish is to apply it to the Duchess of Cornwall. In her youth, the current Duchess and her sister Pippa Middleton were known as the wisteria sisters by some of their contemporaries because they looked pretty, gave off a sweet scent and were determined climbers. She has not transitioned into a clematis: Evison had already launched a new variety of that name while our Queen Camilla held the title.

The Duchess has proved herself, after two seasons in full commerce, as a large-flowered deep violet-blue with a striking white central boss of stamens and a free-flowering habit in early and late summer. Up to 5ft high, the Duchess of Cornwall is an excellent choice to position beside earlier-flowering shrubs. I have just planted her: if I kill her, clematis-wish will make me try to please her a second time.

Robin Lane Fox will be speaking at the FT Weekend Festival on Hampstead Heath, London on September 2. For details go to ft.com/festival

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