EUGENE, Ore. – Clematis vines have three main requirements to thrive – sunlight on their stems and leaves; cool and moist but not wet roots; and support for climbing.
"They need a little special handling at the start, but once established they grow and flower year after year," said Ross Penhallegon, horticulturist with the Oregon State University Extension Service.
To provide ample sunlight, plant the vine where it will get at least six hours of daylight. Filtered shade during the hottest part of the day (July–September) will help keep dark-colored blooms from fading. For a cool root zone, use mulch or organic compost, or plant low-growing shrubs or perennials that will shade the base of the vine. For support use a fence, trellis, tall shrub or another vine, such as climbing rose or wisteria, for support.
Although clematis vines are native to Europe, Asia and North America, more than 200 varieties are available to Oregon gardeners. Some are native to Oregon; the most common is the western white clematis, also known as virgin's bower or old man's beard.
The diversity is stunning. Both evergreen and deciduous, some have large purple, white or pink blossoms, others are small, creamy and fragrant. Others have yellow or cerulean blue bell shaped flowers. Some bloom once in the summer, others in the spring and fall, or only in the fall.
Deciduous clematis is hardy in all Oregon climates. Evergreen varieties, such as sweet smelling, spring blooming clematis armandii, are more sensitive to the cold and perform best in western valleys and the coast. Oregon usually gets a couple of weeks of very cold weather, especially in December or January.
Clematis roots need plenty of room: Dig a large planting hole, two feet deep and nearly as wide. If the soil is very heavy or has lots of clay, add fine bark, manure, compost and/or peat moss. The more organic matter, the better. Add lime if the soil is acidic.
"If your garden tends toward clay, rough up the sides of the planting hole to prevent 'glazing,' which can keep the roots from growing beyond the smooth sides of the planting hole into the surrounding soil," Penhallegon said. The roughing up can also keep water from pooling in the planting hole during the wet season.
Set the plant in the hole with the crown two to three inches below the soil surface. Stake the vine until it has grown enough to reach its permanent support. A new plant should be well-watered, but not overfed. Once established, it will respond well to rose or tomato food, or any fertilizer in the range of 5-10-5 or 5-10-10 or good compost or chicken manure.
As clematis like to keep its feet cool, insulate the root zone of your clematis with a thick mulch of straw, leaves or bark. Or plant a low-growing plant or a rock on the south side of your clematis to help keep the root area shaded.
Pinch out the tips of new shoots once or twice during the first growing season to encourage branching near the base of the vine.
Most clematis will perform better with an annual pruning. Those that bloom during summer on new wood need heavy pruning in winter or early spring, or they will look thin and stringy. The kinds that bloom in the spring on last year's wood can do without pruning, but are better if cut back lightly after they have finished flowering in the later spring or summer.
If given a good start, and a little maintenance, your clematis can live for a long time.