The answer to 'why is my shrub yellowing' is that there are several common causes, including overwatering, nutrient deficiencies, or disease. Yellowing leaves on a shrub can be a sign of stress or an underlying issue that needs to be addressed.
One of the most common causes is overwatering. Excess moisture can lead to root rot and prevent the plant from absorbing nutrients properly, causing the leaves to turn yellow. Underwatering can also cause yellowing, so it's important to maintain consistent soil moisture.
Nutrient deficiencies, particularly in nitrogen, iron, or magnesium, can also lead to yellowing leaves. This can be caused by poor soil quality or an imbalance in the plant's nutrient uptake. Applying a balanced fertilizer or amending the soil may help resolve the issue.
Diseases like fungal infections or pest infestations can also cause yellowing leaves. If the yellowing is isolated to certain parts of the shrub or accompanied by other symptoms, it's best to consult a professional landscaper or horticulturist to diagnose and treat the problem.