Tips On Pruning Clematis

Q: When do I prune clematis and how can I grow a healthy, vigorous plant?

A: Because there are different types of clematis, with different bloom habits, it's vital to know which bloom time the plant has.

-- First, some clematis are early-spring bloomers, and some retain their leaves all winter. The most common of these is the beautiful Clematis armandii, with dark-green leaves and lemon-scented blooms in early spring (February and March).

If the clematis blooms only once a year, and early in the year, prune it directly after the bloom time. Thin the stems to keep the plant from growing into a mass of tangles. But don't touch the early-spring bloomers after about late May, because next year's buds are formed on the wood produced in the summer.

-- If the clematis blooms only once, in summer or fall, often with very large flowers, it produces flowers on wood formed in spring. Prune these vines down to about 2 to 3 feet from the ground after all danger of frost is past, in early spring. Cut back to the lowest pair of strong buds on each stem, and mulch the plants. Examples of clematis of this type are Clematis orientalis, Clematis Viticella, and the familiar large-flowered hybrids related to C. x jackmanii.

-- The third type of clematis blooms in May and July on wood produced the previous spring, and repeats bloom in the late summer or early autumn on wood produced during the current season. Many very common and beautiful hybrids are in this group including "Nelly Moser," "The President" and "Duchess of Edinburgh." This type is somewhat confusing and difficult to deal with because there's constant growth and bud renewal going on during the entire growing season.

One way to deal with these plants is to prune lightly after bloom in late fall, removing tangled foliage but retaining as much as possible of the existing wood for May bloom. Then, after blooming in May, the plant can be renewed by removing about one-quarter of the old shoots, cutting back to a strong bud about a foot from the base of the plant.

Some growers leave these plants entirely alone until they have grown for several years into a tangle, then take out all but a few strong shoots down to the base of the plant. With this method, a season of early-summer bloom is missed while the plant renews itself.

An excellent text on pruning all garden plants, with useful diagrams, is the book "Pruning," by Christopher Brickell (Simon and Schuster, 1979 and subsequent editions). These suggestions for pruning clematis were taken from this text.

Most clematis vines require a steady supply of moisture during the growing season, and do not thrive if they are allowed to dry out during the summer. Mulching, spreading about 2 inches of any well-composted organic material across the roots, will hold some moisture.

Fertilize in early spring with a 5-10-10 granular fertilizer. Or provide liquid fertilizer every three weeks during the active growing season, without overdoing the nitrogen component of the liquid feed. Do not fertilize unless the plant is well watered first. This routine should maintain the plant in healthy blooming condition.

Q: Is it too early to set geraniums outside?

A: Geraniums are real heat lovers, and they'd prefer indoor shelter until temperatures warm more. The traditional time for setting them outdoors permanently is about mid-May. We have had some delicious spring afternoons with summer-like temperatures, but our night temperatures are still down in the 40s or lower. As a compromise, the geraniums could be set outside on warm days and brought inside for the night. They will certainly not die at 40 degrees, but they will fail to grow and thrive when the temperatures drop that low.

Gardening runs Friday in Scene and Sunday in Home/Real Estate. It is prepared by Mary Robson, area horticulture agent; Holly Kennell, Washington State University/King County Cooperative Extension agent, Susan Miller, integrated-pest-management specialist, and volunteer Master Gardeners.