JoAnne Skelly: What’s wrong with my maple?

It’s only August and the leaves of the “Autumn Blaze” maple (Acer x freemanii 'Jeffersred') at The Greenhouse Project are completely yellow. What’s going on?

This maple is a hybrid of silver (Acer saccharinum) and red (Acer rubrum) maples. While it will have brilliant orange-red fall color, the leaves shouldn’t be yellowing in August.

The “Autumn Blaze” is a rapid grower growing three feet per year to a mature height of 40 feet to 50 feet. This fast growth can cause weak branch attachments and breakage. It can also have invasive surface roots.

When I looked at the tree at The Greenhouse Project site, I noticed that all the leaves were completely yellow on the entire tree. Yellow leaves can be caused by various factors including poor drainage. Without good drainage, roots are damaged and cannot absorb necessary oxygen or nutrients and leaves turn yellow. Compacted soil is one reason for poor drainage and also for poor root development. Overwatering in a soil with inadequate drainage can rot roots.

Iron deficiency (chlorosis) is another cause of yellowing leaves. However, chlorotic leaves usually have greenish veins and aren’t completely yellow as The Greenhouse Project tree’s were. Alkaline soils (high pH), which the site has, can make iron unavailable to a plant.

Cory King, The Greenhouse Project manager and farmer, told me that the tree had been overwatered with overspray from the school’s sports’ field irrigation system. The clay soil in which the tree was located was saturated. Once he stopped the overspray, he was able to control the amount of water the tree received. Since the site is also very hot and windy, the poor tree is struggling with an undeveloped or damaged root system and the leaves responded by turning yellow.

Sometimes our first reaction when seeing yellow leaves is to fertilize. However, it is a bad practice to fertilize struggling plants because most inorganic fertilizers are salt-based and can damage roots further.

So, until the tree starts showing improvement, I suggested that Cory put three inches to four inches of compost around the tree out to three feet or four feet. This will provide nutrients in a slow release form that is not salt-based and won’t further stress the tree.

Compost can also improve drainage. Additionally, I recommended watering periodically with compost tea. When the weather cools off, he may want to add an iron chelate or a fertilizer with iron sulfate in it.