Maple trees turning yellow

Are your maple trees trying to tell you something? Are they yellow and look as though autumn has arrived early? As I drive around my neighborhood, I can’t help but notice the vast number of yellowing maple trees. A friend of mine, who also volunteers for our organization, was asking about this common problem, so I decided it was time to write an article about this challenging issue.

Chlorosis is a term for leaves turning yellow due to a lack of chlorophyll. There are a number of reasons tree leaves will yellow including poor drainage, damaged or compacted roots, high alkalinity, and nutrient deficiencies. According to the University of Illinois Extension, a lack of iron either in the soil or available for uptake by the plant is one of the more common reasons for chlorosis.

Iron chlorosis will cause the leaves to turn from dark green to light green to yellow, but the veins on the leaves will remain green. Here in Colorado, we typically have plenty of iron in our soil, so what’s the problem? The plant’s ability to uptake the iron. Plants are complex. There are numerous chemical reactions and interactions that come into play with iron chlorosis. Since we’re not having a class on plant physiology or chemistry today, let’s just say it’s like bobbing for apples with no teeth. We can thank my husband, the chemical engineer, for that funny analogy! Basically, the iron is there, but the plant can’t access it.

So, what to do about it? Do not overwater. Aerate compacted areas. Avoid using plastic sheeting under your mulch. Utah State University Extension offers additional options here: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1884&context=extension_curall, along with a table showing advantages and disadvantages of different treatment methods. Their website states a combination of ferrous sulfate and elemental sulfur can have lasting results and is inexpensive to apply. USU also suggests an iron chelate with EDDHA is effective in our high pH soils; however the benefits only last one year and it is expensive.

You could also try an iron chelate foliar spray with EDTA, but with large trees you can expect spotty results and the benefits are often temporary. Trunk injections can also be done, but are best performed by a certified arborist. You can find one at: http://www.isa-arbor.com/findanarborist/arboristsearch.aspx.

Sometimes you just have to say goodbye. That was the case for our severely chlorotic maple tree. All of the leaves had turned as yellow as sunflowers. We thinned, pruned and treated for several years. It was time for some tough love. We had to let it go. For more pictures showing the different stages of iron chlorosis in a maple tree, check out our Facebook page.

Kelley Rawlsky has an M.S. in horticulture and is the director of Bringing People and Plants Together, an organization dedicated to bringing horticulture education and therapy to the community. For more information: PeopleAndPlantsTogether@gmail.com or follow us on Facebook.

Article originally published in Broomfield Enterprise - July 16, 2017