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clematis group wilt stress dormancy

Clematis Vines Forever

by Mary Jasch

Jim Van Laeken grows over a million clematis vines a year. As owner of Spring Valley Greenhouse, in Zone 5 Walworth, NY, for over 30 years, he propagates them from cuttings. Like anyone who really knows plants, he acknowledges that Zones aren't everything.

For instance: Evergreen clematis are not hardy inland in Zone 5 - just along the coast. The Montana group is hardy to Zone 6. Some early blooming Clematis are hardy to Zone 6, but a late frost in spring takes out the blossoms. For many Montana, the plants do fine but never flower.

Pruning Groups According to Van Laeken:
1 the early group forms buds on last year's growth. These include Montana, the evergreen vines and the Macropetala.
2 moderate group hybrids. All the strongest stems will throw out flower buds from last year's wood. They form buds in the spring.
3 blooms on new wood and plant dies naturally to the ground every winter. Cut plant down to the ground to make room for new growth -- the newer the growth, the nicer the blossoms. Includes Jackmanii hybrids, Viticella, and the evergreen, fragrant and super-hardy sweet autumn C. paniculata.

Flower size has nothing to do with fitting into these groups, he says. All pruning groups contain different types of clematis depending on cross-breeding. The large-flowered hybrids generally belong to groups 2 and 3 and are more susceptible to Wilt. The Viticella group (group 3) and smaller flowering vines are less susceptible.

Growing conditions cause Wilt. Much of it emanates from plants grown in in-ground beds, a European practice. Once a bed becomes infected with Wilt, eradication of the disease is almost impossible.

SVG grows over a million vines of 100 varieties a year on raised benches in 2.5 acres of greenhouses. Each year, they rotate varieties. They have four patented hybrids. “Hybridizing is a long process. It takes five to ten years to introduce a new variety starting from picking it out. We have a little garden where we pick the seeds, sow them, flower them and if we see something unique, take that plant and reproduce it and see if the offspring exhibits the same characteristics, and if it holds true, we patent it," says Van Laeken. 'Sprinkles' is one variety they patented that mutated on its own.

Plant Climbers
The English plant clematis with climbing roses. Integrifolia and Arabella (group 3) weave gently through roses and don't strangle them. Prune both clematis to the ground in early spring, for they bloom on new growth.

C. paniculata climbs 25 to 30 feet on black locust or other open trees with narrow crowns and no lower branches. “It looks like the tree is blooming in fall," says Van Laeken.

Van Laeken certainly knows clematis. He has worked with them alongside his father from the age of 12. While in college he opened his own greenhouse to sell bedding plants. The business expanded to supply garden departments at big name chains, but crashed in the '80s when Free Trade came in. Rather than go bust, he looked for his niche. “We lost three big accounts to Poland. So we built another garden center to build our retail business."ť

Van Laeken says the biggest secret to growing good clematis is digging a big enough hole. “They need to develop a good root system to get a good plant. They like moist, well-drained soil. They have so many leaves and draw so much water, they need a bigger root system to sustain the plant."
“The best clematis I've seen are in a gravelly pit with mulch. Some people actually kill them with too much care."

Clematis have fibrous root systems. Dig a hole 1˝ feet deep for good drainage. Fill it with half soil and half peat moss. If you have a lot of clay, add sand for good drainage.

A mature plant takes a lot of water, he says. If they dry out during a drought they can be shocked into dormancy, but will generally come back. Plants put under a lot of stress trigger dormancy, especially in the middle of a hot, dry summer. Use mulch at their bases instead of ground cover plants, which compete for water.

How to tell the Difference Between Wilt and Stress-induced Dormancy:
Caused by infected stock plants
Happens usually right before plant blooms
Symptoms occur in a day or two
Stems shrivel and can't take up water
Leaves turn yellow from bottom up and look sickly
Remedy -- dig up and trash

Stress-induced dormancy
Cause - hot and dry weather and not enough water
Happens in summer
Symptoms occur in a week or two
Stems don't shrivel
Leaves turn yellow but look healthy
Remedy -- re-locate in well-drained soil (or amend soil) and water well

Botrytis - another killer
Grey mold, leaves turn black
Cause -- wet at night
Prevention -- spray base of plant with fungicide when young for the first month or two.
Best thing -- buy healthy plants from reputable nurseries. Buy an older plant and if it doesn't show any wilt, chances are good it won't.

Look for the wild clematis, the Virgin Bower, C. virginiana, hardy to Zone 6, blooming late summer at the edges of woods and stream banks.

* Visit The Climbery, a Private Garden with 5-6,000 Clematis vines.

American Clematis Society:
Spring Valley Greenhouse:

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published July 10, 2005

Photos to enlarge

Ground Rambler

Evergreen Climber

Ground Cover

Arabella, Courtesy Spring Valley Greenhouse

Fairydust, Courtesy Spring Valley Greenhouse

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