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University of California Cooperative Extension Ventura County
669 County Square Drive, Suite 100
Ventura, CA 93003
Phone: 805.645.1451
Fax: 805.645.1474

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September 4 - Labor Day 
November 10 - Veterans Day
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Iron Chlorosis

This is the term commonly used for iron deficiency. Iron is one of the essential elements for plant growth. Iron is necessary to produce chlorophyll, which is the substance which makes plants green. Chlorophyll is also needed to allow the plant to convert carbon dioxide and water into complex carbohydrate molecules in the presence of sunlight. A plant with iron chlorosis is analogous to a person with anemia.
Iron chlorosis can have several causes. The first and most obvious is lack of iron in the soil. High soil pH is another cause. Many plants have a difficult time extracting iron from soils that have a ph (acid – alkaline balance) above 6.5 – 7 (common on the Central Coast). If the soil has a high calcium content, or is poorly drained, or tends to waterlog, iron deficiency may result. Some plants need low pH soils (5 – 5.5) in order to grow “normally.” These plants are very prone to iron chlorosis here on the Central Coast. Azaleas, citrus, blueberries, gardenias, rhododendrons, hydrangeas, all fit into this low pH loving group of plants. I have seen specimens of Japanese maple, liquidamber, poplar, toyon, and rose from local landscapes showing symptoms of iron chlorosis.
The quick fix for iron chlorosis is to spray the foliage of the affected plant with iron. There are several products available which can be applied to the foliage to help remedy iron chlorosis. Products vary in the amount of available iron, so check the product label for iron content and dosage recommendations before you purchase. To begin a long-term solution to iron chlorosis, you must work at modifying the soil environment to make iron more available. Usually this means lowering the soil pH. This can be done by (1) added compost, (2) adding sulfur – sulfur reacts with elements in the soil to produce acid and in the process decreases pH. Use (3) acid fertilizers like ammonium sulfate, urea, and/or ammonium nitrate. Also (4) manage water to avoid waterlogging the soil. The incorporation of compost (organic matter) mentioned above also helps improve drainage and helps loosen up tight soils. The long-term solutions may take several years of repeated treatment to “fix” the problem. In the meantime help your iron chlorotic plants with foliar sprays.