Linda Geist
  • Sweet autumn clematis.Photo by Katrina Wiese [CC BY-SA 2.0] via Wikimedia Commons
    Sweet autumn clematis.Photo by Katrina Wiese [CC BY-SA 2.0] via Wikimedia Commons
Your Show-Me Garden: MU Extension brings you gardening tips from experts around the state.

COLUMBIA, Mo. – Few flowering ornamentals are as exquisite as the “Queen of the Vines”—clematis.

The majestic splendor of this vertical climber is hard to pass by in nurseries and greenhouses, said David Trinklein, University of Missouri Extension horticulturist.

There are more than 300 species of this member of the buttercup family. Only a few are used as ornamentals, however, and most of those are hybrids. More than 150 years of hybridization has resulted in the clematis we know today, Trinklein said.

Now a show horse, the clematis earned its early stripes as a workhorse across the continents. Europeans used its stems to make fish traps, baskets and wicker. Africans still use its dried roots as tinder to start fires. Historians report that ancient Roman beggars rubbed their hands with sap from clematis leaves and vines to form sympathy-evoking blisters. Clematis still is used as an herbal remedy by some, although its safety is questionable.

Today, clematis is valued for the striking beauty of its flowers. Clematis flowers have no petals, Trinklein said. Their beauty comes from colorful sepals, which in most flowers are rather inconspicuous.

In the case of sweet autumn clematis, its billowy white blooms and delightful fragrance make it one of fall’s gardening joys, he said.

Clematis cultivars are often classified according to the size of their flowers and the time of the year they bloom. The latter is important for proper pruning of clematis, Trinklein said. Pruning enhances this garden beauty’s splendor and rewards the owner with a greater display of blooms.

Gardeners should understand whether their plant blooms on the wood of the previous year or on current year’s growth. This information is available by knowing the pruning category to which their clematis belongs. Care tags supplied with clematis plants at their point of purchase usually list this information.

For the purpose of pruning, the International Clematis Society divides clematis cultivars into three groups, depending on bloom time and vigor:

  • Group I. These cultivars are the first to flower in the spring. They require little, if any, pruning. They produce flowers on the previous year’s growth. Prune only after flowering, when needed.
  • Group II. These cultivars bloom primarily in May and June. However, brief flushes of blooms appear again later in the year on last year’s wood and new shoots. Prune by removing deadwood in late winter and go over the plant again lightly after the first flowers fade in spring.
  • Group III. These are vigorous cultivars that bloom in May or June on current year’s growth. They should be pruned back severely to within 12 inches of the soil in late winter or early spring. Leave at least two pairs of buds on each stem of the plant.

Plant clematis when soil becomes workable in the spring. Dig a hole 6-8 inches wider than the root system of the plant, usually 18-24 inches wide. Work well-rooted manure and a few handfuls of bone meal into the soil to enrich it. Position the plant so that the original soil ball is about 4-6 inches below the surface of the surrounding soil. Use amended soil and water to backfill. If the stem of the new plant is still green and tender, wait until it becomes woody before backfilling.

Clematis roots prefer cool soil. The plant needs about six hours of direct sunlight to thrive, but keep the root system cool by planting in partly shaded areas. Mulch or low-growing plants and ground covers provide shade for heat-sensitive roots.

Clematis use their petioles to climb and “grasp” onto objects such as trellises and fences. Therefore, clematis require some type of support. Fertilize established clematis lightly each spring with a general-purpose garden fertilizer such as 5-10-5.

Timely application of fungicides, good site selection and proper soil preparation prevent stem rot, the most frequently encountered disease of clematis. If stem rot occurs, prune the plant back to the point where symptoms first appear. Slugs like to feed on spring growth. Control them with baits.

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