At least half of the landscape plants we commonly use do not have their origins in desert locations. Plants like hibiscus, rose, Indian hawthorn, passion flower, citrus, pyracantha and many others prefer acidic soils. Without them leaves turn yellow, most often from a lack of iron.

Iron deficiencies are typified by yellowing of the young leaves and new growth. There is a defined pattern to this yellowing. The areas between the leaf veins yellow first, while the veins remain green. This presents a herringbone-like pattern. In time, as iron starvation becomes more acute, even the veins turn yellow and the entire leaf can fade to white. Leaves lower down the stems will exhibit less pronounced symptoms.

We do have naturally occurring iron in our desert soils. The problem, however, is that this iron is not in a soluble, or usable, form for plants. Sulfur is often added in the mistaken hope of acidifying the soil. It doesn't work! Our soils are alkaline due to extremely high levels of naturally occurring calcium, particularly calcium carbonate. To neutralize all that calcium would require an unfathomable amount of sulfur! So what's to be done?

The key to correcting common iron deficiencies is to apply iron in a form that is available to plants. Water soluble iron is available for root uptake by plants and is referred to as chelated iron. Garden centers, nurseries, and horticulture supply stores all carry chelated iron products. The most commonly available brands include; Ferion, Ferriplus, and Sequestar. These products come in smaller quantities designed for the home gardener. Other products such as Sprint 138 (Sequestrene) are sold in larger quantities for commercial landscapers and nursery growers. All of these products provide season long correction of iron deficiencies for landscape plants. Container grown plants may require more frequent applications to keep them iron rich. Don't waste money buying non-chelated forms of iron. Although these products may be well known, and inexpensive, the truth is they just don't work in our desert soils!

Chelated iron products are typically diluted in water and applied to the soil. In addition, iron can be sprayed on the foliage to be absorbed directly into the leaf. When foliar applications are made, a wetting agent or spreader-sticker must be mixed with the iron spray to provide even coating of the leaf surface. Liquid dish washing detergent can be used as a wetting agent. Just add two or three drops to each gallon of spray mix. Chelated iron should be applied during warm weather, when plants are actively growing. Fall and Winter applications are not advised, as cool weather will prevent uptake of the iron.

When fertilizing plants in general, but more specifically iron deficient plants, use an ammonium-based fertilizer. The ammonium in ammonium sulfate (21-0-0) and ammonium phosphate (16-20-0) have the ability to provide some short-term modification of soil pH which is beneficial for the uptake of iron, as well as phosphorous, manganese, and zinc.

Finally, take care to correct nutrient deficiencies, such as iron, in their early stages. The more severe the deficiency, the harder it becomes to correct. 

Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161.
Material originally appeared in Arizona Daily Star gardening column, on June 13, 1999
Return to index