By: Sandy Feather ©2006
Penn State Extension
Q. I have a 10- to 12-year-old clematis vine that has lots of foliage but very few flowers. It has been this way since it first started to bloom. In the fall, I cut it back almost to ground level. It regrows vigorously every spring but does not bloom very much. What can I do to get it to bloom more?
A. It is advisable to prune all clematis annually to avoid them becoming bare on the bottom and carrying all of their flowers high on the plant out of comfortable view. The main object of pruning should be to encourage the plants to produce the maximum number of flowers for your enjoyment, as well as to keep some of the more vigorous types in bounds. There is a good chance that your clematis does not bloom very much because you are pruning it at the wrong time of year.
How and when you prune clematis depends on when it blooms and its growth habit. Horticulturists divide clematis into three groups, based on their time of bloom. Some species flower on the current year's growth, often referred to as "blooming on new wood." Others flower from buds produced on last season's growth, which is referred to as "blooming on old wood." Still others flower on old and new wood. It is easy to look up the proper pruning group if you know the cultivar name or species of your clematis.
Early-flowering species that generally bloom in April and May from buds produced on last season's growth (old wood). They should be pruned as soon as possible after they finish flowering. Avoid pruning them after the end of July, so they have time to produce next year's flower buds before winter sets in.
Start by pruning out any dead, damaged or weak stems. Then prune out the shoots that have flowered. You can also prune out more stems at their point of origin to thin out the plant and maintain a good framework of main stems that flower well within easy view. Avoid cutting into the woody main trunks.
Clematis in Group A include C. alpina, C. chrysocoma, C. macropetala and cultivars, and C. montana and cultivars.
Large-flowered hybrids such as 'Nelly Moser' that bloom in June on short stems from last year's growth (old wood) and often flower again in late summer on new growth (new wood). Because you do get a few flowers after cutting the plant back so hard in the fall, it is likely that yours falls into this category.
This group of clematis should be pruned in February or March. Begin by removing dead and/or weak stems. Then cut the remaining stems back to the topmost pair of large green buds. This cut could be a few inches to a foot or more back from the stem tips.
Plants in this group have the tendency to become bare at the base as they mature. You can underplant with small shrubs or perennials to help conceal the bare stems. Alternatively, you can often force a flush of new growth from the base by cutting the vine back to 18 inches immediately after the flush of bloom in June.
In addition to 'Nelly Moser,' plants in this group include: 'Miss Bateman,' 'Lasurstern,' 'Duchess of Edinburgh,' 'Belle of Woking,' 'General Sikorski,' 'Mrs. N. Thompson' and 'The President.'
Late-flowering species and hybrids, including sweet autumn clematis (C. terniflora). This group flowers on the last 2 to 3 feet of the current season's growth (new wood). Some types begin blooming in mid-June and continue into fall. They are easy to prune because you do not need to maintain any old wood. In February or March, cut each stem to a height of 1 or 2 feet. Although you will be removing good stems and buds, this treatment keeps these vigorous growers in bounds. In addition to Clematis terniflora, plants in this group include: Clematis x jackmanii, C. tangutica, C. viticella, 'Duchess of Albany,' 'Comtesse de Bouchaud,' 'Ernest Markham,' 'Lady Betty Balfour,' 'Madame Julia Correvon,' Perle d'Azur' and 'Royal Velours.'
By: Sandy Feather ©2007
Penn State Extension
Q. I recently purchased a house that came with several clematis vines. I am not positive which cultivars they are. They came up beautifully this spring and have bloomed heavily. But now, two of them have wilted and turned brown - they appear to be dead. Can you tell me what it is, and what I can do to prevent this from happening again? I would hate to lose all of these clematis vines!
A. That sounds like the heartbreak of clematis wilt. This common fungal disease causes the symptoms you have described. It occurs most frequently on the large-flowered hybrid clematis varieties. Species clematis and their hybrids, and small flowered hybrids tend to be more resistant.
Clematis wilt is caused by the fungus Phoma clematidina. It often occurs when the vines are growing vigorously. Succulent, new growth tends to be more susceptible to infection than mature growth that has hardened off.
To add to the heartbreak, clematis wilt often strikes just as the flower buds are about to open. Instead, the entire vine wilts, and then turns brown right down to the ground. It is most common when we have a very wet summer, as we did several years ago, but I have received a number of questions about it this year, too.
On small plants, the entire plant can wilt and die in a matter of a couple days. New shoots can grow from the roots, and often go on to grow and bloom normally, so do not be in a hurry to dig the affected vines out. On large, more mature plants that have many stems, some stems are affected while others are not. Clematis wilt does not always kill the entire plant, especially well-established specimens such as yours.
The best course of treatment is to prune out wilting stems as soon as you notice them, at or even below the soil line. New stems should grow from the roots to replace them. Clean up dead leaves and stems as thoroughly as possible. Dispose of infected stems in the trash or by burning them, rather than throwing them on the compost pile. The fungus can survive in the soil surrounding infected plants. It usually enters healthy stems through a wound, so be very careful when you work around your vines and avoid nicking the delicate stems. When you prune them, be sure to make clean cuts that will heal rapidly. Have a trellis in place for them when they come up in the spring, rather than trying to tie up the tangle of stems that seem to grow overnight when you do not have the trellis in place soon enough. You are guaranteed to break some of the stems when you are wrestling them into place after the fact.
It is also important to provide the proper environment for clematis to grow well. These vines prefer an evenly moist, yet well-drained soil. Heavy clay soil that holds too much moisture around the roots and stems makes them more susceptible to clematis wilt. Clematis performs best when the soil pH (acidity or alkalinity) is near neutral, or 7.0, and when it receives at least six hours of direct sun daily. Although clematis grows and blooms best in full sun, it is important to mulch the roots, or underplant clematis with low-growing flowers or groundcovers to shade their roots. If you use mulch, do not bury the base of the vine with it. Two inches of mulch is sufficient to control weeds and cool the soil. Try to avoid having the mulch physically contact the stems.
If you lose the affected plants entirely, consider planting ones that are more resistant, such as our native virgin's bower (Clematis virginiana), sweet autumn clematis (Clematis terniflora) or one of the viticella types (Clematis viticella), such as 'Ernest Markham,' 'Lady Betty Balfour,' or Madame Julia Correvon. Please remember that resistant does not mean immune. When disease pressure is high and environmental conditions are favorable, so-called resistant plants can become infected, too.