Plant Pathology Infobytes

January 28, 1999
Perk Up Landscape Plants Suffering from Iron Deficiency

The winter months can be a great time for correcting problems observed in a landscape planting the previous season. For example, azaleas, Japanese hollies, hydrangeas, dogwoods, and other woody ornamentals are often affected by iron chlorosis caused by low levels of iron content in leaves. Plants suffering from this condition are sometimes said to have "iron poor blood."

While iron chlorosis won't kill plants, the light green to yellow color of leaves caused by iron deficiency detracts from the appearance of landscape plants. Over a period of several seasons, plants with "iron poor blood" gradually weaken and are more susceptible to invasion by diseases and other pests.

Iron chlorosis is easy to recognize. It causes foliage to become chlorotic, while the leaf veins remain bright green.

This problem should not be confused with nitrogen deficiency, which usually shows up on the lower foliage first and causes an even yellow to light green color of the entire leaf.

Iron chlorosis is most frequently caused by one or a combination of the following factors.

  • The soil pH may be too high. Under higher soil pH conditions (generally at pH's of 5.5 and higher) iron may become tied-up and unavailable to plants. Higher pH's often occur when excessive lime is applied to plantings. Before adding lime to landscape plants, it's always best to collect soil samples for analysis to determine exact amounts needed. Over-application of lime to acid loving plants is a common mistake. So collect that soil sample before adding lime.
  • Another reason for iron chlorosis can be related to mortar (which contains lime) left in soil following home construction. Iron chlorosis commonly appears in foundation plantings around new homes during the first or second growing season.
  • In some regions of the state, the soil pH may be naturally high and iron tie-up occurs as a result. This is a common occurrence on "black-belt" type soils.
  • Poor root growth may also cause iron chlorosis. Healthy plants develop an extensive fibrous root system which extracts iron and other essential nutrients from surrounding soil, but plants with poorly developed root aren't very efficient feeders. Several things may be responsible for poor root growth and lead to the development of iron chlorosis symptoms. These include root rot which often occurs when plants are planted in poorly drained areas, nematode damage, over-fertilization, poor soil preparation at the time of planting, and planting too deeply.

If your landscape plants were affected by iron chlorosis in past seasons, this is a good time of the year to carry out practices to help prevent the problem in the 1999 growing season.

Try to clear up iron chlorosis by adding iron in the form of chelated iron or ferrous iron sulfate (your soil sample report will indicate the amounts of this material to apply per square foot of bed area). During the growing season, immediate results may be obtained by spraying plants with ferrous sulfate or chelated iron (spray at rates recommended on containers for both materials). However, this will usually give short-term results as compared to adding chelated or ferrous iron sulfate to the soil in late winter or early spring.

Before carrying out any of these practices, it's best to collect a soil sample from plantings affected by iron chlorosis to determine the fertility status of your soil. Check by the County Extension Office for information on collecting soil samples.

Soil fertility analysis information will be the beginning information needed to help you and County Extension personnel set up a program which will give long term results in avoiding iron chlorosis problems.



Written by the late Dr. Frank Killebrew

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