The yellowing of rose leaves can have several causes, including:

• Nutrient Deficiencies: Roses need nutrients such as iron, nitrogen, and magnesium. A lack of these can lead to yellow leaves. For example, iron deficiency often causes yellow leaves with green veins (iron chlorosis), which can happen if the soil pH is too high (alkaline) preventing nutrient absorption. Adding iron supplements or adjusting soil pH toward slightly acidic (6.0 to 6.5) can help.

• Watering Issues: Both overwatering and underwatering can cause yellow leaves. Overwatering may lead to root rot and yellowing, while underwatering causes stress and similar symptoms. Proper watering practices with well-draining soil are important.

• Pests and Diseases: Spider mites, aphids, and fungal diseases such as black spot or mildew can cause yellow spots or yellowing leaves. Spider mites leave white webbing on leaf undersides. Removing infected leaves and treating infestations or diseases can help.

• Environmental Stress: Insufficient sunlight, heat stress, or reflected heat can cause yellowing, especially in shaded lower leaves or during hot weather. Providing adequate sunlight and mulching or shading to reduce heat stress may resolve this.

• Normal Leaf Shedding: Older leaves at the base or inside the bush may turn yellow and drop as part of normal growth and light shading by new leaves.

In summary, yellow rose leaves are commonly due to nutrient deficiencies, improper watering, pest or disease presence, environmental stress, or natural leaf aging. Checking soil pH, watering correctly, inspecting for pests, and ensuring sufficient light can help address most issues.