University of Illinois Extension

Clematis

What has often been termed the Queen of the Vines, clematis, can offer rich, striking beauty as does royalty, said Greg Stack, University of Illinois Extension horticulturist.

"At the same time, it can be very temperamental just as some royalty can be," said Stack. "But once you have decided to include clematis in your garden, there are a few things that should be noted so your 'royal resident' will find your garden to its liking."

Clematis are members of the buttercup family and have well over 300 species and countless man-made hybrids in the group. Not all of these are suited to Midwestern gardens and so selection needs to be done carefully. Clematis are mainly woody, climbing plants. They do not attach themselves to supports by twining stems, aerial roots or tendrils.

"However, they attach by twining their leaf petiole around support structures," he said. "Because of this, thought has to be given to providing the proper supports otherwise they will ramble along the ground until they do find suitable support.

"The best supports are those things that are less than three-quarters of an inch in diameter. Clematis petioles find this size to be the easiest to wrap around. Many gardeners find that using heavy fishing line is a good way to get clematis to climb up poles or arbor posts."

If a knot is tied in the line at 12 inch intervals, this will help keep the vine from sliding down the fishing line, he added.

In the wild, clematis is often found growing at the edge of woodlots where they climb through the tree limbs to reach full sun while their roots remain in the shade. Success with clematis starts with proper soil preparation, planting and after planting pruning. Clematis prefers a cool, moist, well drained soil for best growth. They do not like poorly drained soils especially those that stay wet over the winter. While it is true that clematis prefers alkaline soils, they will grow successfully in soils that are neutral (pH 7.0) to slightly alkaline (pH 7.5). To determine if liming is necessary, a soil test should be taken to guide you on how much if any lime needs to be added. Annual liming is not suggested as over liming can lead to other nutrient deficiencies.

"When preparing the planting site be generous with the planting hole," he said. "Dig a hole at least twice as wide as the pot the plant is in and at least twice as deep. This allows for adequate organic matter to be incorporated into the site, a key to good root development. When planting, plant deep. Place the crown of the plant at least two to four inches below the surface of the soil. This will help with the production of stems from dormant buds below the soil and also helps the plant recover if stems are injured by animals or mechanical means."

Newly-planted clematis should be pruned back to about 12 inches in the spring following planting. This pruning will encourage new shoots to develop and will produce a fuller, bushier vine with many more stems and a not so bare bottom.

Clematis like to be fed but not overfed. Fertilizing in the spring with a general purpose fertilizer right after pruning should carry the plant through the season.

"Because clematis prefers cool soils, some type of mulch should be used over the root area," Stack said. "Planting a low perennial ground cover near the plant often works well or organic mulch can be used.

"Apply about four to six inches of mulch at the base of the plant keeping the mulch about eight inches from the stems to avoid stem rots."

Now comes the mystery for many gardeners when growing clematis: when, how and where do I prune? Stack answered that pruning clematis is not complicated and even if done incorrectly it is not fatal. The worst that can happen is you will either delay flowering or flowering does not occur for a year.

Clematis is divided into groups or categories for pruning purposes. They are designated as A, B, C or 1, 2, 3, or hard, half pruning or none depending on what source you are reading. In any case, always look at the tag that accompanies your plant. It will often make mention of the pruning category your plant falls into. Take note and there will not be any doubts.

For group A, these plants flower on "old wood" or last season's stems. For these varieties only light pruning is done in the spring to remove dead stems. Another pruning opportunity occurs right after the plant has finished blooming. Prune in late spring or very early summer. The resulting new growth now becomes next season's flowering stems.

Group B clematis flower on both old and new wood. Because of this, it can make pruning a bit more challenging. Prune lightly in spring removing dead and weak stems. The largest flowers will be produced on the old wood while new growth will provide bloom for late season. If a group B clematis ever needs major pruning to rejuvenate it, a hard cutting back can be done right after spring flowing and still have plenty of time for the new shoots to provide a fall show of blooms.

Group C is the easiest. Here you grit your teeth, grab your pruners and cut the plant down to eight to 10 inches. By doing this, you will ensure a lot of vigorous shoots from the base and a nice, full plant covered with flowers. Many group C clematis are often not pruned hard enough and the result is a rather "trashy" looking vine with lots of tangled stems.

"One problem that is frequently seen with clematis is clematis wilt," he said. "This problem has been attributed to a fungus and is most damaging early in the growing season when the plants start flowering. Leaf spots and partial stem rot occurs resulting in wilted stems.

"This can happen slow or fast. Fungicides have been used as a preventative control, but once the plant is affected the only suggested control is to prune out affected stems at least 2 inches below the point of infection. Most experts agree that clematis wilt is not fatal and most will re-sprout from buds located lower down on the stem."

To get you started with clematis or to add to your current collection, here are a few suggested varieties that exhibit good performance and interesting flowers: