Soil Health

• The health of soil is a fairly fragile factor and may be severely affected by something as simple as excessive rain. When leaves begin changing colors and dropping, there are a few soil-based problems that may be the cause. Compacted soil is particularly common in potted plants and those grown in highly populated areas. Soil that is too tightly packed will not permit proper airflow or drainage, which will drown roots and prevent water and nutrients from reaching the plant. Foliage will often turn yellow, then brown and black as the disease progresses, and will eventually lead to leaf death. Soil correction should be attempted by thoroughly mixing in compost that is rich in organic matter. This will improve drainage and make the soil lighter for better airflow to roots.
  
  

Disease

• Fungal and bacterial infections are perhaps the most common problem in the gardening world. They infect almost every plant type, including evergreens, in just about every habitat in the world. They usually lead to plant death if not treated quickly. Heavy rains or humidity create excellent conditions for these diseases to thrive, and they will quickly over run a healthy plant. Most blight diseases -- evergreen shrub, tip blight and fire blight -- will cause leaves to die, while mold, including powdery mildew, botrytis fruit rot and root rot, may cause both black and dying leaves. Anthracnose is a group of diseases that cause leaf wilt, discoloration and death, and it will infect most parts of evergreen and deciduous trees. It may be found in just about every region in the United States.
  
  

Leaf Scorch

• Leaf scorch is a common problem amongst evergreens and most plants with lush foliage. It presents with a discoloration of the leaves, usually starting with yellowing at the margins, then browning as the problem progresses. If left untreated, the leaves will grow dark, become brittle and drop. Leaf scorch is often associated with too much fertilizer, but it may also be the result of nutrient deficiency, injury, shock or soil problems. Growers should fix the problem as soon as possible and prune away any damaged foliage and stems to make way for more healthy growth.
  
  

Salinity

• Excessive amounts of salt, whether in the soil, fertilizer or water given to an evergreen, may have extremely damaging effects on foliage. Leaf wilting is among the most common symptoms of salinity problems, and may be followed with leaf discoloration -- yellow, brown and black are all common. Salt is one of 16 elements required for a plant to thrive, but when present in high concentrations, it will throw osmosis out of equilibrium. The plant will release too much water, causing dehydration and the associated leaf wilting. This problem is fairly easy to diagnose, as wilting will occur even when the plant has regular watering. Treating may require the addition of compost to the soil or changing the water source. Avoid using water from a softener, as salt concentrations may be higher.