If you grow Clematis, at some point you will encounter Clematis Wilt.
What happens when Clematis Wilt strikes is fairly dramatic, and almost overnight the plant will go brown, and parts or all of it will collapse.
The plant will look as if it is very dry, all brown and drooping but in fact it is the dreaded wilt. The general view is that Clematis wilt is caused by a fungus ( Calophoma clematidina [syn Phoma clematidina, Ascochyta clematidina]). It is also true to say that scientists are not 100% sure this is the cause as Clematis wilt also seems to occur where there is no evidence of fungus. In these cases it is usually environmental causes which include how the Clematis has been planted, and it's growing environment, see below.
Whatever causes Clematis Wilt what to do about it?
The first point is the choice of Clematis to grow. Resistance to Clematis Wilt varies in the different types of Clematis. Those most susceptible are the large-flowered hybrids, such as C. Jackmanii (illustrated) C. Nelly Moser, C 'Comtesse de Bouchaud' which tend to be the late flowering Clematis with large open flowers. Resistant to wilt are C. Montana, Alpina, Orientalis, Macropetala, and Tangutica (see Types of Clematis for illustrations of these types of Clematis.)
Secondly, how and where you plant a Clematis may also help to prevent Clematis wilt. It is important to plant Clematis deeply. The rule of thumb is to ensure the root ball is at least 5cms below the soil level. Deeper planting is to aid root development and the Clematis will develop better roots and shoots from the base. How to plant Clematis information and video.
"Right plant Right place" will also give the Clematis the best chance of being healthy and fending off Clematis wilt. Clematis belongs to a group of plants which likes its roots in shade and its head in the sun. In addition, Clematis have a preference for fertile soil on the moist side. Given that Clematis prefer the ground moist with some shade, a good mulch around the roots is helpful and also physically shading the roots. It is possible to buy specifically manufactured clay pots to protect the roots, which can be expensive, and an alternative is to use a spare slate. Take great care not to damage the root or stem, which is also said to be a possible cause of introducing wilt.
It is also important to keep Clematis well watered, not just after planting, but during the summer especially if it is dry. If Clematis become dry, it will cause stress to the plant and as a result become more prone to wilt.
There is no chemical control to prevent or cure wilt. All you can do if wilt strikes is to cut and prune off any effected stems and leaves. Remove all infected parts and clean the secateurs or cutters to ensure no cross infection.
It is very disheartening when wilt strikes. Often the Clematis is about to get into full swing with lots of buds and then starts to wilt. The good news is that it will recover but you do have to be bold and remove all infected parts.
The image at the top is to show how fickle Clematis can be and gardening advice. Illustrated is a C. Jackmanii which is planted and growing up a wall without any signs of wilt. Any plant growing next to a wall will be a dry area, with a rain shadow and yet this mature Clematis looks splendid. So if your heart's desire is to have a lovely, large flowered clematis growing up a wall, and it has to be a late flowering variety, take a chance you may get lucky.
Even if you follow all of the above recommendation, it is not easy to stop Clematis wilt, and sometimes it seems pretty random.