What is Chlorosis?

Chlorosis is a yellowing of leaf tissue due to a lack of chlorophyll. Possible causes of chlorosis include poor drainage, damaged roots, compacted roots, high alkalinity, and nutrient deficiencies in the plant.

Iron chlorosis is the most common micronutrient problem of ornamentals, shrubs, vines, small fruiting plants, trees, and certain types of lawn grasses, such as centipede grass. Leaves of affected plants are yellow, light green, or white with distinct green veins. In severe cases, the leaves may be entirely white. The margins of severely chlorotic leaves often scorch and die during hot periods. Some willows, oaks, and other plants express iron deficiency with distinct black spots between the veins. Iron deficiency chlorosis may be persistent or it may vary during the season or year to year depending on environmental conditions. If iron chlorosis is persistent for several years, individual limbs or the entire plant may die.

What Causes Iron Chlorosis?

Iron chlorosis is the result of the inability of the plant to extract sufficient iron from the soil. This inability to extract iron is caused by soil pH, which is the measurement of acidity of the soil. When a plant is suffering from iron chlorosis this is an indicator that the soil is too alkaline for the the plant. The soil pH ranges on a scale from 1 to 14. That being said, most plants thrive at a soil pH between 4 and 8. Any lower or higher and plant life just won't grow.

Iron chlorosis is common in many types of soils and is exaggerated by excessive soil moisture, soil salinity, high concentrations of phosphorous, and relatively high concentrations of copper, manganese, and zinc in the soil, low or high soil temperatures, large additions of organic matter, or inefficient root function caused by nematodes or fungal pathogens. The most important factor is the presence of lime in the soil as a predisposing factor. Lime is used to "sweeten" the soil, or make it more alkaline. Too much lime in the soil can lead to chlorosis in plants that prefer a more acid soil.

Plants vary in their ability to obtain and utilize iron. This is particularly evident when adjacent plants may show marked differences in chlorosis. Some plant species are capable of obtaining iron from alkaline soils whereas others cannot be grown successfully in native high pH soils.

How To Treat Iron Chlorosis?

Preventing and controlling iron chlorosis is not that difficult. Because iron chlorosis is caused by a soil that is too alkaline, the treatment involves making the soil more acid.

The following are recommended procedures for controlling iron chlorosis:

Conduct A Soil Test

 First, to know the soil pH of your soil, it would be a good idea to test or have your soil tested to determine average pH.

Research the Plant

Before you do anything to remedy the problem, it's important to know the soil pH that the plant you are treating prefers. This, and knowing the existing soil pH, will tell you how much of a nutrient you will need to apply to properly adjust pH to level the plant will thrive in. 

To find soil pH that a specific plant prefers, you can first check to see if the plant exists here in Wilson Bros Gardens. If so, you will find the soil pH range requirements on it's product page. 

Correcting Chlorosis

Once you know that iron chlorosis is the problem, and is the culprit for the yellowing leaves on your plant or lawn, you can use an Iron product, such as High-Yield Iron Plus Soil Acidifier to correct the problem. 

I usually don't make specific product recommendations, but Iron-Plus is a very good product that contains 16% iron and 13% sulfur. Other products in the marketplace contain much less iron and sulfur and come at a higher price. 

Chelated compounds must be placed into the root zone to be most effective. Incorporate lightly into the soil or irrigate in. Applications are most effective when made in the spring to coincide with the first flush of growth. That said, for a plant that continue to produce new growth during the warm season, any time of year is okay.

Note: Iron compounds sprayed on leaves give the most rapid but temporary response. Usually green spots can be seen on the leaves a few days after spraying. Repeated applications are necessary as new foliage appears. Chelated iron compounds or 0.1% ferrous sulfate can be applied as foliar sprays. Use a spreader-sticker to obtain better results. Avoid applications when fruit is present on fruit-bearing plants because staining may occur.

Soil Moisture Management

Water management is probably the most important consideration when growing plants in soils that tend to be alkaline. In excessively wet or poorly drained soils, the chemistry of the soil changes and iron becomes unavailable. Irrigation applications should wet the plant root zone and should not be repeated until the soil moisture has been reduced by plant use and evaporation. Frequent irrigation in heavy clay soils or cold temperatures often results in a persistent deficiency of iron.