Dead leaves on clematis usually mean one of two things. Lack of water is one and clematis wilt is another. Or could be both. Treating the plants with a fungicide such as Bonide's 3 and 1 Rose and Flower Care in spring may take care of the problem. Planting Clematis deep, a couple of inches deeper than the soil level in the pot, helps stave off this fungal disease. Regular watering will also help. Best And Happy Yardening, Nancy.