CORVALLIS, Ore. – As they climb up trellises and trees unfurling large, lusciously colored flowers, clematis put on a special show in the garden.
These garden favorites need a little special handling at the start but once established clematis (clem-ah-tis or cla-mat-is) grow and flower year after year.
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, according to Oregon State University Extension Service experts.
To provide ample sunlight, plant the vine where it will get at least six hours of daylight. Filtered shade during the hottest part of summer 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, small tree, tall shrub or another vine, such as climbing rose or wisteria.
The diversity of clematis is stunning. There are 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. Bloom time varies from once-bloomers in spring or summer, twice bloomers in spring and fall, or only in fall.
Deciduous clematis are hardy in all Oregon climates. Evergreen varieties like sweet-smelling, winter-blooming Clematis armandii, are more sensitive to the cold and perform best in western valleys and the coast.
When planting clematis, give roots plenty of room: Dig a large hole, 2 feet deep and nearly as wide. If the soil is very heavy or has lots of clay, add fine bark, manure and/or compost. 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. 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 clematis 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. Feed three times a year in spring, summer and fall.
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 perennial or place 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.