In plants showing symptoms of iron chlorosis leaves begin to turn yellow except for the midrib and veins, which remain dark green. The problem can progress to the point where the leaves become very pale and turn brown at the tips. Iron chlorosis is a common problem, especially for plants that like acidic soils, which have a low pH. If the pH of the soil is too high, which is often the case with our alkaline western soils, iron chlorosis can result.
Iron chlorosis is an iron deficiency that can be caused by several other things too, such as roots that are damaged by tilling, dry soil, and sandy soil with insufficient organic matter. Tilling damage and dry soil make the roots less able to take in nutrients. Plants that are set near the base of buildings can develop iron chlorosis because of lime that leaches from the cement foundation of the building, causing the soil pH to rise.
Short-term solutions include addition of an iron chelate to the soil or as a foliar application. Check the soil pH and correct it if necessary and if practical. In many cases, iron is present in the soil in adequate amounts, but plant roots cannot absorb it because the pH is not in the appropriate range for the plant. To help solve a chronic iron deficiency problem, add 1-2 inches of compost to the soil each year, or add sulphur or peat moss if the pH is too high. Acid-loving plants can also be mulched with evergreen needles, such as pine needles, which will leach some acids into the soil.
Selection of ornamentals and trees adapted to the type of soil found in your yard can save problems in the long term. If soil is "improved" so certain plants can be grown, the improvements will need to be maintained each year. You may wish to obtain plants suited to the spot, rather than planting species that require high input of materials and labor over time. Plants in conditions for which they are not suited are under continual stress, subject to stress-related pest and environmental problems. A soil test can provide information that will help your nursery professional recommend species adapted to your site. Also consider temperatures (winter lows and summer highs), wind, etc.
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Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997