Members of the buttercup family, clematis vines come in around 250 different species. Most clematis plants lose their leaves in the fall, but some keep their foliage year-round. The wilting of evergreen clematis could be due to several different reasons.
Clematis vines need approximately 1 inch of water every week during their growing season. If given too little water, the entire plant will to wilt.
According to the Kemper Center for Home Gardening, the fungus Ascochyta clematidina will cause the disease clematis wilt. Symptoms include sudden wilting, often at or around the same time the flowers begin to bloom. Within days, foliage and stems will turn black.
Drought stress can be avoided with adequate watering. Watering deeply once a week helps ensure safety from drought stress. For plants suffering from clematis wilt, watering more will only damage the plant further. If other garden plants have not wilted, then it may be clematis wilt, or some other disease. Remove and destroy all infected stems and foliage. Plants may take one to two years to fully recover from the disease.