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 vines!

A: It 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 of 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 (C. terniflora) or one of the viticella types (C. 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.