Clematis plants are woody, vining plants that produce brightly coloured flowers with thin petals during the spring and summer. The flowers' colours range from white to red to purple. Yellowing clematis leaves may indicate a nutrient deficiency.
A number of nutrients are required in the soil for the healthy production of green leaves. A deficiency in any one nutrient may be enough to cause leaf yellowing. However, it is more likely the soil lacks variety of nutrients. Regular feeding with a balanced fertiliser helps keep leaves healthy. A soil test in the early spring determines what nutrients are low.
Nitrogen, phosphorus and potassium are three essential nutrients for plant growth. Nitrogen is essential for the production of healthy green leaves. A lack of nitrogen in the soil leads to weak, yellow leaves and even premature leaf loss on the clematis plant. Adding a fertiliser containing nitrogen to the soil around the clematis restores the leaves to health and prevent defoliation. Applying fertiliser in the early spring avoids yellowing leaves.
Iron and Calcium
Iron and calcium are minerals needed to produce dark-green leaves throughout the growing season. A lack of these nutrients in the soil leads to producing weak, yellow leaves. It often takes the form of chlorosis, which is yellowing between the veins of the leaves. Applying an iron- and calcium-containing fertiliser to the soil around the clematis plant restores these nutrients.
Other Causes of Yellowing
Although nutrient mineral deficiencies are a common cause of yellowing leaves in clematis plants, there are other problems contributing to unhealthy leaves. If fertiliser was properly applied and the leaves remain yellow, check the plant for signs of disease, such as dieback of vines and branches or weak flower production. Look for pests on the undersides of leaves. Clematis plants grown in full sun are susceptible to scorch, which causes yellow leaves.