Evergreen hedges are stable garden plants that provide colour all year, unlike deciduous plants that lose their foliage in the winter. The plants liven up the otherwise bare and dull landscape with natural colour and attractive forms. Improper growing conditions or environmental stresses affect the health of evergreen hedges, causing the foliage to turn brown. Not only do affected leaves stand out, in most cases they indicate an underlying problem that requires immediate attention to prevent spread.
An evergreen hedge planted in overly wet or poorly draining soil may experience browning. Excessive soil moisture prevents the roots from absorbing oxygen and nutrients, thus hindering plant growth. Stressed leaves turn yellow first, then turn brown if the problem is not rectified. The plants also develop root rot, a condition that causes roots to turn black and slimy and rot completely. Transplant the evergreen hedge to a well-draining spot, if possible, or irrigate the soil when the surface feels dry.
Severe drought also causes an evergreen hedge to turn brown and become stressed. Insufficient soil moisture or fluctuations in irrigation schedule dehydrate the plant, especially during dry weather or in the summer. Because of the unavailability of soil moisture, roots fail to absorb and transport it to different parts of the thirsty plant, causing the leaves to appear brown and dry. Drought stress is most noticeable during late summer, especially in hedges planted in gravel, sand or heavily compacted soils. Follow a regular irrigation schedule to provide an evergreen hedge timely applications whenever necessary. Increase the frequency during the summer when the evaporate rate is higher, and mulch the soil heavily to help retain soil moisture. Use a soaker hose, which encourages roots to travel deep into the soil in search of water.
Winter injury is perhaps one of the most common reasons for partial or complete browning of evergreen hedge foliage. Exposure to dry winds, freezing temperatures and frost cause the foliage to turn brown, reddish-orange or golden-yellow. Called bronzing, the process does not cause serious damage to the evergreen hedge, which bounces back to its original health and vigour when given proper care. Install windbreaks to protect evergreen hedges from sudden or fast winds and frost.
Stressed evergreen hedges become susceptible to insect infestations that damage the leaves and stems, causing them to turn brown. Pests such as aphids, spider mites, mealy bugs, miners and weevils attack evergreen shrubs and sap essential juices from the foliage. Some pests secrete honeydew on infested leaves, which serves as the breeding ground for sooty-mould fungus. Leaves covered with the black substance fail to perform photosynthesis, turning brown before falling prematurely. Treat pests with insecticide or neem oil and adopt good cultural practices to prevent future outbreaks.