Leaves that turn color early probably on stressed trees, says St. Lawrence County Cooperative Extension educator
Saturday, August 27, 2011 - 6:47 am

By PAUL HETZLER

When you’re under stress, do you turn different colors—red in the face, perhaps? Ever had someone tell you that you look peaked, or maybe green around the gills?

Chronically stressed trees start changing colors earlier in the season than other trees do, and for that reason late August is the time to make a tree-stress inventory on your property.

Stressed trees color-up ahead of their compatriots because of their balance sheets—in nature, nothing lives beyond its means. For trees, costs include leaf, twig and root production and nighttime respiration. Income is the sugars made from sunlight, water and carbon dioxide. As summer wanes, longer nights drive up costs while shorter days reduce income until it’s no longer profitable to operate, and deciduous trees close shop for the season. 

Trees in stressful conditions struggle to procure the raw materials—water and nutrients—for their business, which makes them less profitable overall. Street trees, for example, experience elevated soil temperature, limited root area, soil compaction and road salt, all of which cause water stress. All too often, shoddy planting leads to a poorly formed root system, and a tree that could live for hundreds of years dies for no apparent reason after just 20 or 30 years.

Even in a natural environment, trees can have difficulty. For example right now you can probably find a few native red maples along waterways that have turned red. This is because fluctuating water levels tax their root systems: drown ’em one day, dry ’em the next, repeat. Also, wetland soils are often nutrient-deficient.

Sometimes there’s a brightly colored branch on an otherwise green tree, which means business is good except for that particular branch office. In these cases, a section of the root zone is having trouble (though it’s not always the root directly below that branch).

If one of your trees has hung out its “See You Next Year” sign early, you can be sure it’s facing chronic stress. Keep it well-watered next year—a good soaking over the root zone once a week during dry spells. You may want to consult a tree-care professional for further treatment options such as root-zone aeration or fertilizing. But try not to stress out about it.

Paul Hetzler is a forester and a horticulture and natural resources educator for Cornell Cooperative Extension of St. Lawrence County.