What to do if plants have iron chlorosis
Iron chlorosis is a condition seen in many trees, shrubs, and flowers. It is caused by the plant not being able to take up enough iron from the soil to meet its needs. The symptoms are very distinct. The leaves turn yellow while the leaf veins remain dark green. Roses, linden trees, silver maple, some hydrangeas and some varieties of spirea are especially sensitive to iron chlorosis. But other plants are also susceptible.
Soils in most of North Dakota are medium to high in pH (7.5 and higher) which is caused by lime in the soil. The high pH converts the iron to a chemical form which is not available to plants. Soil compaction and poor drainage can also cause iron chlorosis, but not as often. The soil around the plant may not be short of iron, but the high pH makes the iron take on a form which is not available to up the plant.
Iron chlorosis is quite difficult to treat. This is especially true when dealing with the condition in larger trees and shrubs. Elemental sulfur has been used to lower the pH of a very small area for a relatively short amount of time. But it needs to be done often. And the rooting zone for even a small tree can be 20-plus feet in diameter. And the sulfur needs to be applied at quite short intervals to maintain the lower pH.
Chelated iron products will give relief from the problem. These products can be soil applied. This method will give slower, but longer relief from chlorosis. But this must be a repeated annually as the soil lime will slowly bind the unused iron in the soil. Chelated iron products are also made which can be sprayed on the leaves of the plant. This will give quick greening (two weeks) of the affected leaves. But applications will need to be repeated. A combination of the two treatments will give the best results over a longer period of time.
For more detailed information about iron chlorosis, the Extension Office has copies of circular F1868, Iron Chlorosis in Trees. Stop in to pick up a copy or call 857-6444 and ask to have a copy mailed out.
Ken Eraas is horticulture assistant with NDSU Extension Service/Ward County. He can be reached at kendell.eraas @ndsu.edu.