If your desert landscape plant has yellow leaves, it may have a deficiency called iron chlorosis. Learn about the symptoms, causes, and treatments here.
If you have a plant with yellow leaves, figuring out the cause can be challenging. Causes of yellow leaves include over-watering, under-watering, too much sun, too little light, too hot, nutritional deficiencies, and more. It would almost be funny if it wasn’t so frustrating. 😬
But if the leaves on any of your plants look like the picture above — yellow with green veins — your problem is almost certainly iron chlorosis (i.e., iron deficiency).
Let’s take a look at the symptoms of iron chlorosis, why it happens, and how to treat your plants that have it.
What Causes Iron Chlorosis?
Desert soils are loaded with calcium carbonate (CaCO3) which causes the pH to be high, usually around 8 to 8.5. And when the soil pH is high (i.e., alkaline), iron in the soil forms insoluble compounds that plants can’t use, leading to iron deficiencies.
Iron chlorosis is especially common in non-native plants. Native plants have evolved to grow in alkaline desert soil and have developed ways to absorb the iron they need from high pH soils.
Other factors that can contribute to iron chlorosis include overwatering, compacted or poor draining soil, and the use of landscape fabric.
Diagnosing Iron Chlorosis
People are often surprised to learn that our “poor” desert soil is actually loaded with minerals and that nutrient deficiencies are rare. (What our soils lack is organic matter, not minerals.)
In the desert southwest, there are really only two mineral deficiencies that you’re likely to encounter in your landscape plants — nitrogen (N) and iron (Fe).
Here’s how you can tell these two deficiencies apart.
Iron deficiency affects new leaves and is characterized by yellow leaves with distinctly green veins.
Nitrogen deficiency affects old, lower leaves. Leaves turn yellow-green and eventually drop off the plant. Importantly, the veins turn yellow as well.
Susceptible Plants
Popular non-native landscape plants that commonly develop iron deficiency include:
- bottlebrush
- citrus trees
- crepe myrtle
- gardenia
- hibiscus
- Indian hawthorne
- plumbago
- pyracantha
- roses
Occasionally, a native plant will develop chlorosis, and that is usually due to overwatering or poor drainage. Non-natives that sometimes develop chlorosis include Mexican honeysuckle, hopbush, and fairy dusters (pink and red).
How to Fix Iron Chlorosis
There are three ways you can address iron chlorosis, but only one works well and is practical.
Acidify the Soil
You can add a soil acidifier (usually in the form of sulfur) to try and lower soil pH, but this is not a practical solution. It’s nearly impossible to permanently change your soil’s pH. This remedy works best on a small scale such as in containers or raised vegetable beds.
Apply Foliar Iron
Spraying a foliar iron spray actually works quite well and can green up your leaves in short order. But the results are temporary since the iron stays in those leaves and doesn’t move around the plant.
This means you’ll have to spray any new leaves as they emerge. In fast growing plants, this can be every few weeks.
Keeping up with this is tricky since iron must be sprayed when the weather is cool or it will burn the leaves. Its recommended that you spray when temperature is below 85℉.
Apply Iron Chelate (Recommended)
The recommended treatment is to apply a chelated iron supplement, following the instructions on the label. (Too much iron can be as detrimental as too little.) Chelated means that the iron molecules are bonded to another substance to create a form that plants can utilize.
This is easy to do, but you must use the right kind of chelated iron supplement since most are not formulated to work in alkaline soil.
Important! Use the Right Iron Supplement
Don’t grab the first iron supplement you find at at your garden center, hardware store, or online retailer.
Most iron supplements are designed to be sprayed on lawns for greener grass in other climates and are not formulated for alkaline desert soil.
There are several different forms of chelated iron. Look for one that states Fe-EDDHA or EDDHA* on the label. (EDDHA refers to the chelating agent used to make the iron absorbable.)
Very few iron supplements are EDDHA chelated, and they cost significantly more than the others. You may question whether it’s worth it.
In a word, yes.
EDDHA is by far the best form to use in the desert. Other less expensive forms may work well elsewhere, but are not effective in alkaline soil.
One name-brand product that contains this form of iron is Fertilome Chelated Iron EDDHA 6%. Here’s a picture to help you find it.
* The EDDHA in Fe-EDDHA is a chelating agent that stands for ethylenediamine-N,N′-bis(o-hydroxyphenyl) acetic acid.
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for 15 years.
