Here is a genus that many gardeners find ridiculously easy to grow but that some consider simply too fickle and demanding. Sadly, lots of people give up on clematis without ever understanding their needs. Still others grow them in wild, tangled masses with all the flowering on top, unaware that different types of clematis have different growth habits and need a little help from a sharp pair of pruning shears to maintain law and order and encourage vigorous flowering.

First, the name. It’s derived from the Greek word klema, meaning various climbing plants. And, yes, it is pronounced CLEH-ma-tis, not clem-AH-tis.

All types of clematis enjoy deep, well-drained, but consistently moist, soil enriched with lots of organic matter such as compost, leaf mold, aged or dried manure; they also appreciate some damp peat moss being worked into the root area. Clematis vines dislike acidity in the soil, preferring instead a neutral or slightly alkaline pH level. In vary acidic soil, it’s a good idea to work in a little horticultural lime. Vines benefit from an extra dollop of manure topdressing in fall, and a slow-release granular fertilizer in early spring.

Although they enjoy full sun, clematis roots like to be cool, so a thickish summer mulch is useful. Compost is great but grass clippings are fine too, provided fertilizer is used to replace the nitrogen that grass clippings leach from the soil as they break down. Alternatively, plant the vine behind a low perennial or a rock that will shade the roots without curtailing the plant’s growth.

Clematis are best planted in spring so they can make as much root growth as possible before winter. Cultivate the soil very deeply where your plant is to go, working in your choice of organic material. To plant, invert the pot very carefully, supporting the surface and stem with one outspread hand while gently sliding the pot off the root mass. Place carefully in the hole. Backfill well with soil and water. Unlike other plants whose crowns must not be buried when planting, clematis don’t mind being planted deeper than they were in the pot. Keep the stake support in place for the first year, slanting it toward whatever vertical surface the clematis will be climbing.

Vines require lots of water during active spring growth, and they’ll often remind you by hanging their heads when thirsty. Try not to wait that long. And don’t expect abundant flowering from your new clematis for 2-3 years, until it becomes well established.

Unlike climbing roses, which need to be tied to some upright support like a trellis or arbor post, and ivy and climbing hydrangea which adhere to their supports by aerial rootlets, clematis climb by twining their leaf petioles (slender little side-stalks from the main vine) around whatever they can grasp on the way up. Without intervention from the gardener, a chunky trellis or fence board is not always conducive to this twining habit, but netting, wire, steel mesh, or the assistance of a piggy-back shrub, vine or tree is.

The fact is, clematis like company. In my own garden, I rarely plant a climbing rose without making the hole big enough to accommodate a companion clematis. With the pale-pink rose ‘New Dawn’, I grow a mauve clematis called ‘Hagley Hybrid’; the vine either twines itself up the rose canes or flops forward onto a clipped boxwood shrub beside my front stairs. And in the back garden, a ‘PJM’ rhododendron that flowers in early May must do double-duty as a summertime host to Clematis viticella ‘Etoile Violette’, which displays its gorgeous purple flowers across the rhodo in July.

Viburnums, apple trees, junipers, euonymus – almost anything is enhanced by clematis blossoms. Just make sure the clematis is planted far enough away from the host to secure its own root zone, free of competition from the other plant’s roots.

There are certain types of clematis that do not twine via leaf petioles. One is Durand’s clematis, Clematis x durandii, the vibrantly colored vine which is a cross between common ‘Jackmanii’ and the herbaceous Clematis integrifolia. These plant grows to about 6 feet (2 m) and is best draped over a host shrub. In New York’s Central Park Conservatory Garden, I loved the way it was trained over a crimson Japanese barberry.

Pruning Your Clematis

Ah, pruning. If you want clear instructions, invest a little money in one of the excellent reference books on clematis. I especially like English specialist Raymond Evison’s books. If you prefer to fumble along on your own, here are the basic rules:

The so-called large-flowered clematis that begin to flower in late spring or early summer do so on ripened – that is, last year’s – wood, so must not be pruned other than to remove weak or dead stems, or above a strong pair of buds to maintain a desirable height. They may produce a few blossoms on new wood later in the season too, with the double-flowered varieties usually producing single flowers the second time around. Popular large-flowered cultivars are ‘Vyvyan Pennell’ (double lavender), ‘The President’ (single purple),. ‘Henryi’ (single white), ‘Duchess of Edinburgh’ (double white), ‘Bee’s Jubilee’ (single pink with darker stripe), ‘Ramona’ (blue), ‘Royal Velvet’ (violet-purple with red stripe) and ‘Nelly Moser’ (single pink with darker stripe).

Small-flowered clematis that bloom in summer do so entirely on the current season’s growth, so the previous year’s stems should be cut back in early spring to about 1 foot (30 cm) from the ground, just above a plump pair of buds. Growth will emerge from this level and often from new shoots below the soil surface as well. Commonly grown small-flowered clematis include the most widely available one, purple ‘Jackmanii’, pink ‘Comtesse de Bouchaud’ (not Bouchard as it’s often listed), mauve ‘Hagley Hybrid’, red ‘Ernest Markham’, red ‘Ville de Lyon’, white ‘Huldine’, blue ‘Perle d’Azur’ and cultivars of Clematis viticella such as ‘Polish Spirit’, ‘Warsaw Nike’ and ‘Etoile Violette’.. It’s these varieties that tend to become a tangled mess with sparse flowering if left unpruned. They’re also the easiest to grow.

Spring-flowering clematis Clematis alpina, with its lovely, nodding blossoms in blue or rose-pink and Clematis macropetala and their cultivars produce flowers on old stems, so should be left unpruned, except for tidying up the vine immediately after blooming finishes. Spring clematis are very hardy and easy to grow.

Clematis texensis, the summer-flowering North American species and its cultivars, e.g. ‘Duchess of Albany’, bloom on new wood so are pruned like the small-flowered group, i.e. hard in early spring.

Late-flowering clematis like Clematis tangutica with its nodding, yellow lantern-like flowers in summer and fabulous sweet autumn clematis, Clematis terniflora, with its masses of tiny, white, scented blossoms on stems that can reach up to 20 feet (6 m) both bloom on new growth, so should also be pruned hard in early spring.

Herbaceous clematis such as Clematis recta ‘Purpurea’, Clematis heracleifolia and Clematis integrifolia die down each winter and emerge anew each spring, just like a peony or phlox. Their top growth can be cut off in fall like any perennial. In spring, C. recta ‘Purpurea’ tries to stand erect for several weeks, then collapses in a heap. I let this one drape itself over the edge of the stairs to my sundeck, but it would also be very effective cascading over a stone wall.

Because the needs of the various types of clematis are so specific, it’s a good idea to group them according to their habit. For example, many gardeners love to plant two clematis vines side-by-side and let them weave together and the flowers intermingle. That’s a lovely idea, but much easier with two small-flowered cultivars which can be pruned hard in spring; it would be too difficult to tell a large-flowered cultivar’s stems from a small-flowered vine.

By and large, clematis are pest-free, but there is one heartbreaking disease, clematis wilt that can ravage a seemingly healthy vine, causing it to collapse overnight, just as it is coming into flower. Occasionally, only one stem will be affected, but often the entire vine wilts from the top down. Clematis wilt is thought to be caused by a fungus that somehow enters either through the root or stem. It is generally only a problem with large-flowered clematis (‘Nelly Moser’, ‘Ramona’ etc.), so the problem can be avoided by growing small-flowered cultivars, especially the problem-free Viticella hybrids. And since an affected vine will usually regenerate from the roots, clematis experts stress the importance of doing the initial planting a few inches below soil level, so the vine has a chance to sprout from a new bud. Since the fungus spores may be in the soil, it’s a good idea to change the planting location to a new spot, if possible, cutting back the top growth and carefully lifting the plant to its new location.

There is a clematis for every taste, every month of the growing season, every garden, and every gardener, whether a novice or true aficionado. The hard part is controlling the urge to buy more than one (ten? thirty?) of the lovely plants known as “queen of the vines”.

Adapted from a column that appeared originally in Toronto Gardens

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