“We planted three river birch trees in our front yard three years ago, and some friends recently pointed out the trees’ leaves have a yellow cast to them. When we looked more closely, there were some leaves turning brown too. What can we do to help our trees?”

— Sonia Patel, Bolingbrook

Your trees are probably suffering from chlorosis, which is a yellowing of normally green leaves due to a lack of chlorophyll in the leaves.

Chlorotic plants may only show symptoms in a few branches, or the whole plant may be affected. The first sign of chlorosis can be a subtle paling of the green color of the foliage, which you may not have noticed in the trees’ early years. This off-green color can progress to a more distinct general yellowing over the course of a growing season or over several years. It is generally the result of a nutrient deficiency caused by a lack of available nutrients or the inability of the tree to take up the nutrients.

In the Chicago region, some of the most common causes of chlorosis among trees and shrubs include nutrient deficiencies that are related to soil alkalinity (high pH), drought, overwatering, poor drainage, and compacted soil. Chlorosis is more pronounced on birches when they are planted in heavy clay, compacted soil, or high pH soils that impede the tree from absorbing iron and manganese.

The affected leaves can be stunted and have browning along the edges. Soils that are compacted and poorly drained, roots that have been damaged by construction, and drought can also affect root growth and may contribute to a chlorosis problem. Hot and dry weather is hard on trees and can exacerbate chlorosis symptoms.

There may be a combination of factors causing your trees to decline. River birches generally develop chlorosis in alkaline soils with a pH higher than 6.5. You can have a soil test done to determine the pH of your soil, but it is most likely higher than 7. The trees’ roots cannot absorb iron because of the high pH of the soil.

Other nutrient imbalances in the soil can cause chlorosis symptoms too. Birch trees also perform poorly in compacted soil because they have shallow root systems, and compacted or heavy soils prevent the trees’ roots from absorbing nutrients. Heavy watering of your lawn coupled with a heavy, poorly drained clay soil can bring on chlorosis too.

Weather and your gardening practices can affect the development of chlorosis. Birch trees prefer moist soil that is well drained — soils that hold water and stay wet for extended periods of time can cause chlorosis. River birches may develop yellow leaves in the summer during hot and dry periods without supplemental watering. These trees will also shed dead leaves in response to these hot and dry periods.

The trees’ foliage can be sprayed with chelated iron to help green it up in the short term, but this is not a long-term solution. The soil, ideally extending beyond the drip line of the tree, can be treated annually with elemental sulfur to help lower the pH of the soil at a rate of 1 1/2 pounds of sulfur per 100 square feet of bed in spring and fall. It may take a couple of years to see any results.

There are also other commercial products that arborist firms can use to treat the soil or inject the trees to green up chlorotic plants. It is difficult to lower the pH of the soil enough to dramatically improve the performance of a birch tree. Results depend on the type of soil you have and its pH level.

You will get better results when you start a program of applying sulfur and other soil amendments as soon as you see chlorosis in the leaves. Since your trees are relatively young and are already having issues, you may want to replace them with a different tree that will be better adapted to your site’s growing conditions. Selecting the right plant for a garden’s growing conditions and design objectives is an important first step for success.

For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.