(Editor's Note: This article was originally published on January 27, 2008, Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
I can’t think of a single flower that has such a variation in form, foliage, size and blooming season except for the clematis.
Clematis is a member of the Ranunclaceae (Buttercup) family. The word is from the Greek and means “vine”. This plant has about 250 species and numerous hybrids.
Site choice is very important in the successful growing of this plant.
The older varieties need at least 6 hours of sunlight each day in order to thrive. Some of the new hybrids will grow in partial shade; if your site falls into this category, choose the variety carefully. This plant prefers a neutral pH of 7.0 to slightly acidic 6.6-6.8. It does best in well drained rich soil with plenty of organic material.
Although most of these plants prefer full sun, their roots like to stay cool. Use a low growing ground cover around the clematis or mulch well to keep the sun from the root area.
When planting make sure the crown of the plant is 2 inches below the surface of the soil. A handful of bone meal or super phosphate in the planting hole will help establish root growth.
You’ll need some type of structure on which the vine will grow. A fence or trellis works well. I like to plant them as an accent plant with my climbing roses where both plants can climb together. They also go well with climbing hydrangeas.
Maintence of clematis is pretty straight forward, water deeply once a week during hot, dry weather. Replenish mulch each spring to a depth of 2-3 inches. This will keep the roots cool and conserve moisture. Fertilize early in the spring and every 3-4 weeks after. Hold off on the fertilizer when the plant is in bloom. Stay away from fertilizers that are heavy in nitrogen; use an all purpose with an N-P-K of 5-10-10 or a 6-12-12.
One of the most asked questions that I receive in my newspaper column is how to prune clematis.
Clematis are divided into 3 groups. It’s critical that you know what group your plant is in to successfully prune and not to lose a lot of the blooms.
Group A or 1 Early Flowering
This group of clematis bloom on “old wood” that is the buds are produced from growth the previous growing season. These should be pruned as soon as the flowers fade, but no later than July. This will allow sufficient time to produce next year’s blooms. You may prune out old vines to reduce size if desired. Do not prune the heavy woody trunks. Some examples of plants in this group are Clematis alpina, C. macropetala, and C. montana.
Group A or 1
Group B or 2 Large flowered Hybrids
This group consists of the early blooming large flowered types. These are large, single, double or semi-double blooms. These produce flowers on both “old wood” and “new wood” the current year’s growth. You’ll get 2 flowering periods from this type. These should be pruned in late winter or early spring. You may also may prune in late fall after they go dormant.
Some of these are ‘Nelly Moser’, 'Lasurstern', and C. florida.
Group B or 2
Group C or 3
These bloom on “new wood” or the current year’s growth. The first 2 or 3 feet of growth. These normally begin to bloom in June and will continue throughout the summer. Prune in late winter or very early spring. Cut them back to a height of 2-3 feet. Examples are Jackmanii hybrids, C. viticella, and C. integrifolia.
Group C or 3
Some of the diseases that you might encounter while growing clematis are a fungal disease called ascochyta clematidina more commonly known as “clematis wilt”. This disease is mostly seen on the large flowering hybrids. The stem turns dark and collapses just prior to flowering. Usually removing the stem below the blackened area will control this disease.
Powdery Mildew is another disease that often appears in hot humid weather. You can treat this with application of a good fungicide. Good air circulation will deter this problem.
Earwigs and aphids are the most common insect pests to be on the lookout for,
For those of you in USDA zone 6 and lower. I like to mulch my clematis in the late fall with shredded leaves to a depth of 4-6 inches. This will prevent the crown of the plant from heaving out of the ground during freeze/thaw cycles.
Stay tuned for an upcoming article by my DG writing team mate Susanne Talbert. She will tell you more about Clematis-An introduction to Cultivars.
Pruning diagrams coursety of Michigan State University Extension