Iron Chlorosis by Mary Small

Do your plants have “the yellows”? I’m referring to the sickly yellow-green or bright yellow leaf color that plants sometimes develop. The problem is called chlorosis, the loss of the green pigment, chlorophyll.  In our climate and soil, the most common chlorosis is iron chlorosis, caused by the lack of available iron in the soil or a plant’s inability to absorb it.  Deciduous plants develop pale green or yellow leaves with green veins. As the problem progresses, newly developing leaves are smaller than usual.  Angular brown spots form between the veins and leaf margins can turn brown and crispy. Branch tips may die as well as the entire plant, if left untreated. Evergreens and lawns may have an overall yellow cast.  Lawns may also have scattered bright yellow patches.

Iron chlorosis on maple leaves

Some environmental conditions can cause or aggravate iron chlorosis because they interfere with normal plant functions, including the uptake of nutrients. Overwatering is probably the most common cause of iron chlorosis symptoms in the landscape.  While water is essential, too much drives out soil oxygen and kills or damages roots.  Dead roots means no (or reduced) nutrient absorption.
Soil compaction, the pressing together of soil particles, is another common cause.  Compaction reduces the amount of oxygen and water penetration into the soil.  It increases the amount of runoff and heat conductivity. You guessed it: this kills or injures roots, making it tough to perform their water and nutrient absorption job!

So what is a plant owner to do? 
•    Avoid planting species that are very susceptible to iron chlorosis including silver and amur maple and pin oak. Aspen, cherry and birch are also susceptible.
•    Add organic matter to the soil before planting to help improve soil condition.  Plant based compost is best. For more information: http://www.ext.colostate.edu/pubs/garden/07235.html
•    Core aerate turf and around the base of affected vegetation to increase water and oxygen penetration.
•    Apply iron to the soil or plant.  Recommended techniques work better in some situations than others, depending on the plant, soil condition and severity of the problem. 

For specific instructions on iron applications, see this fact sheet published by Utah State University:
 http://extension.usu.edu/files/publications/publication/ag-so-01.pdf