Grapevine showing chlorosis of the leaves.

Our hollies are showing signs of iron deficiency. What should we do? -Paul

Iron deficiency, also called iron chlorosis or lime chlorosis, starts with a yellowing of the leaves in between the dark green veins, giving the leaves a spidery look. Over time, the leaves become whitish and start to die back, eventually resulting in stunting and dying back of the entire plant. Unfortunately, these symptoms can also be caused by other deficiencies and conditions, so it’s important to make sure you have the right diagnosis.

The very first step in diagnosing and treating iron chlorosis is to do a soil test. Your agricultural extension center can help with soil testing, and they may also be able to test a leaf sample to determine which mineral is missing. While you may find that your soil is actually lacking in iron, the problem may well be caused by:

• Alkaline Soil: When soil pH gets above 7 or so, many plants are unable to absorb iron as well. This sometimes happens accidentally when gardeners over apply lime around acid-loving plants. Correcting the soil pH will improve nutrient uptake and may be all the fix you need.
• Mineral Imbalance: Too much of a good thing can also cause problems. Your soil may have too much of some minerals, and not enough of others, which makes the solution a lot more complex. Simply adding iron won’t help unless you correct the overall mineral balance in the soil. This can particularly be a problem in clay soils, where nutrients are scarce and may not have enough organic material and microbes to be absorbed properly.

Hollies are particularly susceptible to iron chlorosis, along with other acid-loving plants like azaleas, blueberries, oaks, and rhododendron. I would begin with a soil test, then follow all the recommendations given to correct your soil. If the soil test does indicate an iron deficiency, you can find iron supplements at your local garden center. You’ll have a couple of choices:

• Treat Plant: Liquid iron (iron sulfate or chelated iron) is available in a liquid form that you spray directly on the plant foliage. This quick fix doesn’t have lasting results, but it can help get your plant back on track while you work on a better solution.
• Treat Soil: Powdered or granular chelated iron is the best option for soil amendment. Sprinkle it around the root zone of the plant according to package instructions. Phosphorus overload can contribute to iron chlorosis, so if your supplement also contains fertilizer, make sure it’s phosphorus free.

Iron supplements are usually applied in spring, and although the plant will start to look better in a few weeks, it’ll need TLC over the next year or so to stay healthy. Be sure not to spill any of the supplement on your sidewalk – it’ll stain!

Further Information

• Soil Test (video)
• Straight Talk About Iron Deficiency and Plants (Texas A&M Extension)

Tags: , alkalinity, azalea, blueberry, chelated iron, holly, iron deficiency, iron sulfate, oak, oil, Rhododendron