Sustainable Landscape News Distributed 01/25/10
By LSU AgCenter Horticulturists Dan Gill, Allen Owings and John Young
Iron chlorosis is a common and sometimes serious problem in landscape plants across Louisiana.
Azaleas are frequent victims of iron chlorosis, but roses, gardenias, sasanquas, camellias, citrus, blueberries, petunias and pansies also are susceptible. Even, centipede grass and St. Augustine grass can show signs of iron deficiencies. You usually will see iron chlorosis developing on plants during the active growing season and toward the end of a growth flush.
Why does iron chlorosis occur? Chlorosis occurs because of nutrient deficiency. Many soils in Louisiana have adequate levels of iron, but the iron becomes unavailable for plant uptake at high pH ranges.
The degree of acidity or alkalinity of a soil is expressed in terms of pH values. A soil pH of 7.0 is considered neutral. Soils having a pH above 7.0 are alkaline or basic while soils having a pH below 7.0 are acid.
Typically, iron chlorosis occurs on acid-loving ornamental plants, such as azaleas, when soil pH goes above 6.5. If a soil is high or very high in phosphorous, iron chlorosis can be a problem even in a more acid soil.
Diagnosing iron chlorosis on ornamental plants is relatively easy. The first area affected is new growth – or terminal leaves. At first, leaf veins are darker green than the area between the veins. Then as the deficiency progresses, the leaf areas between the veins become yellow.
Before treating a soil to alter pH or prior to applying iron fertilizer, eliminate the possibility of the condition being caused by over-watering or poor drainage, which occurs occasionally. Otherwise, the problem can be overcome by supplying the plants with a soluble form of iron, preferably through the foliage, although it could be done through a soil application.
Iron chelates and inorganic compounds containing soluble iron, such as ferrous sulfate, are the principal materials that supply iron. To lower soil pH, which makes the soil iron more available to the plants, use ferrous sulfate, aluminum sulfate or elemental sulfur. Sulfur products, however, should never be applied unless a soil test recommendation justifies this corrective action.
Visit LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is near the intersection of Burbank Drive and Nicholson Drive (Louisiana Highway 30) in Baton Rouge, across the street from the LSU baseball stadium. For more information, go to www.louisianahouse.org and www.lsuagcenter.com/lyn.
Rick Bogren