Yellow Hue Means Iron Is Lacking

New leaves on rhododendrons or azaleas sometimes unfurl bright yellow rather than green. The yellow is made all the more striking in contrast with the leaf veins, which remain green. Although many find that attractive, it is the symptom of a problem that can kill a plant.

You might say that the plant has “tired blood,” because the symptoms are of iron deficiency. Plants don’t have blood, of course, but iron is needed for chlorophyll, which makes plants green (and actually has a similar structure to blood hemoglobin).

Before putting iron pills or rusty nails in the soil, know that there is probably enough iron already in the soil. Deficiencies usually occur when a plant cannot absorb iron because the soil is too wet or not acidic enough, or has too much clay in it.

Plants in the heath family--rhododendron, azalea, mountain laurel and blueberry--need soils that are especially acidic and well-aerated, and thus prone to iron deficiency.

Pin oak, gardenia and citrus also are commonly afflicted. Problems frequently occur on “foundation” plants near homes because of alkaline-building rubble buried near the foundation.

Correcting soil conditions takes time, perhaps more than an ailing plant has to offer. In such cases, give the plant iron sulfate or iron chelate. Sprinkle the powder on the soil, then water it in thoroughly. A shrub or small tree needs a quarter of an ounce to two ounces, depending on the plant’s size; a potted plant needs about a half-teaspoon.

For a plant severely deficient in iron, spray iron solution, mixed according to the package directions, directly on the leaves. Within days the leaves will turn dark green.