Damage From High pH to Oaks

High Oak pH

• A high pH level in the soil damages an oak tree through the condition known as iron chlorosis. In severe cases, the foliage will eventually turn brown and fall to the ground. Iron chlorosis develops as the leaves are deprived of the appropriate amount of iron necessary for them to maintain a healthy, green vigor. A lack of iron interferes with the conduction of photosynthesis.

Cause

• The oak's production of chlorophyll, the chemical element that provides the green hue of each leaf, is also hindered. Iron chlorosis is not the result of too little iron in the soil; rather it is the inability of the tree to properly absorb the iron due to a pH level that is too high. A level of 6.5 or higher renders most trees and shrubs incapable of taking up the healthy amount of iron they need.

pH Definition

• pH measures the alkalinity and acidity of soil. A level of 7.0 is considered neutral, with soil below 7.0 being acidic and soil above 7.0 claiming alkalinity. If the leaves of an oak are turning yellow and falling prematurely, and the tested pH level of the soil is 7.0 to 7.5 or above, then an iron deficiency is present.

Management

• A high pH level and iron chlorosis is primarily an aesthetic problem affecting the beauty of the foliage. It rarely is fatal to the oak, but if the problem persists for several years, the vigor of the tree may decline and dieback of limbs can occur. The application of a chelated iron compound directly on the soil or the spraying of the foliage with iron chelate or sulfur helps to restore an appropriate amount of iron to the tree.