Question
I have many boxwoods and euonymous that are being drained of color and dropping leaves. I'm frantic because I will have to replace so many. Too late to stop damage? How can I protect the few that are remaining? Thanks so much!

Answer
Hi Jan,

Since you don't mention any insects, etc. I can only speculate that you have seen none on these plants.  So, the plants may have some kind of nutrient deficiency.

Boxwoods and others grown as shrubs may require supplements of iron or nitrogen from time to time to maintain the vibrant green color.  But chlorosis (yellowing) can be caused by many things.  So, here is a list of things to observe and do.

1. Monitor the problem. Many factors can cause leaves to become chlorotic. Therefore, before assuming the problem is lack of iron, have the problem diagnosed. Weather conditions and extreme changes in soil moisture may induce temporary symptoms of yellowed leaves. These symptoms may disappear as conditions normalize. Persistent chlorosis, however, needs attention. Plants commonly associated with chlorotic symptoms include holly, hydrangea, apple, blackberry, blueberry, cherry, grape, arborvitae, birch, boxwood, lilac, rhododendron, azalea, sweet gum, pin oak, and other oaks.

2. Use a foliar feeding for temporary results. Spraying the foliage with an iron compound will correct leaf chlorosis temporarily. Iron sulfate, iron chelate, and soluble organic iron complexes are used. Spraying will not affect leaves produced later in the season. Several sprays at intervals of 2 or 4 weeks may be needed to keep developing foliage green. The corrections will last only one season and will not change the underlying deficiencies that are soil-related.

3. Give your plants good growing conditions. Longterm correction of iron chlorosis requires good soil. Improve the soil surface by mulching with 2? inches of organic materials such as leaf mulch or compost. Also, ensure good drainage. The soil pH should be measured with a soil test. An alkaline soil is often the cause of iron chlorosis because it limits the solubility of iron in soil water.

4.Adjust the soil pH to make the iron available.The best long-range solution for correcting iron chlorosis in soils that are too alkaline is to make the soil more acid by lowering the soil pH. A pH of 6.0 to 6.5 is desirable for most plants. As low as 4.5 is recommended for azaleas, rhododendrons, and blueberries. The soil can be made more acid by the addition of sulfur, aluminum sulfate, or iron sulfate. Iron chelates, ferrous sulphate, aluminum sulphate, or sulfur can simply be spread on the soil surface and allowed to dissolve into the soil by watering and rainfall. This method requires more material, but is practical and feasible for the home gardener and may last several seasons, though the initial results are slow. Quicker effects may be seen if the chemicals are worked into the soil taking care not to cultivate too deeply so as to damage plant roots. Another method is to use water-soluble materials which can be injected into the soil with a root feeder.

So, Jan, I cannot answer your question easily as I don't know the cause of the chlorosis.  Since both euonymous and boxwoods are exhibiting the same symptoms, that suggests a problem with nutrients rather than a pathogen as many pathogens are quite specific to host.

It would be to your advantage to have a soil test to determine the pH and the nitrogen level. You may supplement the soil by adding a mulch high in organic matter, such as leaf mulch or compost.  If the pH is too high (too basic), then the iron may not be available to the plants, thus the chlorosis.