The answer to 'hedge yellowing' is that it is a common issue caused by a variety of factors, including nutrient deficiencies, disease, or environmental stress. Yellowing leaves on a hedge can be a sign of nitrogen, iron, or other nutrient deficiencies. It can also be caused by fungal diseases, pests, or environmental factors like drought, frost, or excessive sun exposure.
If the yellowing is isolated to a few leaves, it may be a normal part of the plant's natural cycle and not require any action. However, if the yellowing is widespread or the leaves are turning brown and dying, it could be a sign of a more serious issue that needs to be addressed. In these cases, it's best to consult with a professional landscaper or horticulturist to diagnose and treat the problem.