GV?Gardeners: Iron deficiency in landscape plants

This time of year one of the most commonly asked questions is, “Why are my plant leaves yellowing?” There may be a couple of answers for non-native plants grown in our alkaline soils.

If the entire leaf is yellow, the problem could be a need for nitrogen. This shows from the bottom of the plant on old growth.

An application of ammonium sulfate, ammonium phosphate, or any complete garden fertilizer can add nitrogen. Follow label directions.

If, however, the youngest leaves are yellowing yet the veins remain green, iron deficiency is likely the problem.

As iron deficiency becomes more severe, the entire leaf may become nearly white and progress to older growth as well.

Leaves may eventually die and drop off, even if a general fertilizer has been used.

Also called iron chlorosis, this condition is found where soils are highly alkaline, as in our desert.

The high pH of the soil “ties up” iron in the soil, making it unavailable to plants.

Iron is required for the formation of chlorophyll in plant cells and serves as an activator for photosynthesis.

During this season, high soil temperatures and high light intensity can also increase iron chlorosis problems.

If your plant has a severe problem and you need a quick fix, applying liquid iron to the foliage will work for a short time.

To ensure thorough coverage on the leaves, add a few drops of liquid dishwashing detergent to the spray.

This spreads the iron solution evenly, providing uniform coverage.

Green can reappear within 48 hours after the foliar spray is absorbed by the leaves.

Chelated iron is the best solution and lasts the longest.

This is a soluble form of iron that plants can absorb through their roots even in alkaline soils.

There are less expensive forms sold in garden centers, but they are ineffective in desert soils.

The most commonly sold form of chelated iron is Sequestrene.

Mix the iron chelate with water according to the package directions, and pour around the plant.

Apply to the drip line of trees and shrubs, which is where they take up nutrients and water from their roots.

Because these products can leave difficult stains, avoid getting any on sidewalks, patios, driveways or brick.

Within one week after this application, the plant should green up and stay green for the rest of the season. If not, a second treatment can safely be made.Acid-loving, non-native plants are the victims of iron deficiency.

Among the vulnerable are popular plants such as bottlebrush, pyracantha, nandina, hibiscus, privet, photinia, Indian hawthorn, gardenia, hydrangea, roses, peach and citrus trees.

Native and desert-adapted plants are able to get the iron they need despite alkaline soil.

When next you make new choices for the landscape, keep in mind that native plants actually help you with their maintenance, by their remarkable adaptations to desert conditions.

Mary Kidnocker is a Master Gardener who writes frequently about the subject from a local perspective. Her columns are featured each Sunday. She is currently president of The Green Valley Gardeners.