Riverbirch with Falling Leaves

Mother Nature’s Moment - August 2018

by: Lesley Bruce Smith, ISA Certified Arborist

Healthy Riverbirch losing leaves.  Photo by Lesley Bruce Smith

Healthy Riverbirch losing leaves. Photo by Lesley Bruce Smith

Over the last week or so we have received a number of calls and have noticed with our own Riverbirch that there are a lot of yellow leaves on the ground. This spring we had an unprecedented spring of cool temperatures and lots of rain, and then more rain. All that weather triggered the trees to produce an equally unprecedented number of leaves, or in tree language “food producing evapo-transpirators” which translated means that leaves not only produce food for the tree from the sun’s energy but they transpire water through the tiny holes they have called stomata. Those stomata can open and close to allow more or less water to get through depending on the temps. The stomata are closed up in mild cool damp spring weather but on a 90F July or August day those leaves’ stomata are wide open and letting lots of water through. When that happens day after day the smart trees start to shed leaves to preserve precious water resources. They can afford to do that because they have lots of extras to spare.

When looking at any trees with yellow leaves on the ground before autumn, I immediately look up. It is alarming to see yellow leaves around your tree early in the season but what is more important is what is happening in the crown of the tree. Are the leaves in the crown predominantly healthy and green? Does the tree look happy with a full leaf cover? Then you have nothing to worry about. Try to resist the temptation to over water. Once every three weeks for about 8-12 hours during droughty periods is all the watering that is needed for your trees and if they are mulched you probably don’t even need to do that.

If your tree leaves in the crown are yellow or chartreuse looking there may be other problems going on and you might benefit from a call to your Arborsmith. We are having great success with a new mineral treatment for chlorotic Riverbirch trees who do not like having their roots in clay alkaline soils. 

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