Unlike deciduous plants that drop their foliage before winter, evergreen shrubs retain their leaves and liven up the landscape all year round. Yellowing foliage on evergreen shrubs indicates a problem that requires immediate attention before the entire plant turns yellow. Identify the problem and correct it so you provide the plants optimal growing conditions they need to thrive and flourish.
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Too little or too much water causes the leaves of an evergreen shrub to turn yellow and appear stressed. Overly wet soils that do not drain well prevent rain or irrigation water from penetrating through, thus creating a puddle at the base of the plant. The water prevents the roots from absorbing oxygen, causing the foliage to turn yellow. To overcome this problem, plant the shrub in well-draining soil. Conversely, under watering also increases stress on a plant, especially during dry periods with prolonged sunlight exposure, causing the leaves to turn yellow. Follow a regular irrigation schedule for your evergreen shrub and provide a controlled flow of water when needed.
Nutrient deficiency causes leaves to turn yellow and eventually die, if left untreated. Imbalanced pH level, iron deficiency or low fertility cause yellow foliage. Symptoms of iron deficiency include yellow leaves with green veins. Test the soil to determine its current pH value and amend it according to the shrub's requirements. Spray an iron chelate foliar spray over leaves to correct iron deficiency.
Pests can damage an evergreen shrub and cause its foliage to turn yellow. If the yellow leaves on your shrub fail to regain their natural color despite proper cultural practices, root nematode may be the culprit. The tiny pest thrives in the soil and chews on the host plants roots. Because no chemical control methods exist, the best ways to deal with root nematodes are prevention and maintenance. Practice good sanitation, reduce plant stress and remove damaged plants or parts immediately. Other pests include spider mites and aphids that pierce the foliage of shrubs and suck essential juices, causing them to appear yellowed and stunting overall growth. Treat such pests with insecticidal soap or neem oil.
Some diseases are responsible for causing yellow foliage on evergreen shrubs. Early blight causes the leaves to turn yellow. Early symptoms of anthracnose cause foliage to turn yellow and wilt. Left untreated, the yellow leaves deepen in color and turn brownish-red. Yellow mottle virus causes yellow splotches on leaves of evergreens. Root rot disease manifests itself as yellowed leaves. Treat diseases with fungicide whenever possible, prune infested parts of the plant and practice good sanitation to reduce plant stress that makes the shrub vulnerable to the disease.
Other factors responsible for yellowing of evergreen shrubs include over or under fertilizing, transplant shock, physical injury, excessive sunlight exposure and natural aging process.
- College of Agriculture, Home Economics & Allied Programs: Yellow Leaves, Causes
- Master Gardener Online: Why Are My Plant's Leaves Turning Yellow?
- University of Illinois Extension; Yellow Leaves Can Indicate Plant Problems; Sandra Mason; 2007
- Utah State University; Iron Chlorosis; Sherman V. Thomson, et al.; 1994
- University of Georgia Extension; Azalea Leaves Turning Yellow?; Willie O Chance
- ACES; Nematode Pests of Annual and Perennial Flowers, Herbs, Woody Shrubs, and Trees; Austin Hagan
- Alabama Cooperative Extension; Dieback and Canker of Camellia; Austin Hagan