Iron Chlorosis

Iron Chlorosis is a common nutritional disorder of many woody trees and shrubs in Idaho. It is characterized by leaves turning yellow, except for the veins, which remain green. New foliage is undersized and pale.

Typically, Idaho soils are alkaline having a high pH level. In alkaline soils, nutrients such as iron are often bound within the soil chemistry, making them unavailable to the plant roots. Additionally, clay soils make the problem worse.

Changing the soil pH around a rooted tree or shrub is not a quick process. If a plant is severely affected, consider spraying your foliage with a chelated iron; however, this only works on the leaves sprayed so the effect is temporary and does not benefit the entire plant. For effectiveness and overall plant health, the soil must be acidified by applying chelated iron to the ground and watered in. Depending on the severity of the iron deficiency, several applications may be required. 

Once plants have returned to good health, the maintenance of the correct soil pH level is essential. This is generally done by treating the soil with elemental sulfur yearly. Elemental sulfur will reduce the alkalinity and maintain the happy median that most plants prefer.