Effect on plants: Most plants grow well in slightly alkaline soil (pH 7.0 to 8.0). However, in soils that are more alkaline than 8.0, some plant nutrients, including iron and manganese, become insoluble and are not available to plants even though they are present in the soil. Plants growing in soil that is too alkaline for them develop yellow areas between the veins on their newest leaves. Older leaves usually remain green, unless the plant has been growing for some time in soil that is too alkaline.

Acid-loving plants: Plants that are adapted to acid soil, such as azaleas and rhododendrons, may show symptoms of iron deficiency even when the soil is slightly acid.

Over-limed soils: If soil that is naturally acid has so much lime added to it that the pH rises above about 7.2, plants may show iron deficiency symptoms.

Decreasing soil alkalinity: Make soils more acid by adding aluminum sulfate, ferrous sulfate, or soil sulfur. Add 2 pounds per 100 square feet, wait 2 weeks, then test the soil pH. Reapply these acidifying amendments until the desired pH has been attained. Maintain acidity by using a fertilizer that has an acid reaction in the soil. Alternately, select plants that are tolerant of alkaline soil from the list in Plants That Will Grow in Alkaline Soil (pH 7.5 to 8.4).