Clematis (Clematis spp.) is a large group of evergreen and deciduous vines from the buttercup plant family. Clematis come in a wide range of flower colors and sizes. The vines thrive in regions with cold winter weather. Leaf spotting and yellowing are among the commonly encountered clematis problems.
Yellowing foliage on clematis is seen on plants that are excessively fertilized with high-potash fertilizers. This creates a manganese deficiency in plants, leading to yellowing foliage. Leaf spot is a fungal disease caused by numerous fungi.
Leaf yellowing is characterized by the foliage turning yellow between the veins. This is commonly seen early in the growing season. Leaf spots start with the appearance of very small dots or raised yellow to brown irregular patches on foliage. These spots and patches gradually multiply and cover the entire leaf surface.
Cure yellowing foliage in clematis by incorporating Epsom salts or magnesium sulphate in the soil at the rate of 1 oz. for every 10 square feet, as suggested in "An Illustrated Encyclopedia of Clematis." There are no fungicides recommended for leaf spots, as the disease is mostly aesthetic in nature. Keep plant area clear of weeds and fallen foliage to prevent pathogen from spreading.