Why Are My Trees Blowing Bubbles?

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After some hard rains this past week, I received a call from a very concerned citizen, wanting to know if their tree was in trouble.  The citizen was frightened that this had happened and didn’t want to lose the trees, because there was a pile of soap bubbles coming from the base!  My first thought and initial response was… YOU CANNOT BE SERIOUS ABOUT TREES BLOWING BUBBLES??  Of course, the only thing I could do was ask if they could send me pictures to see what was going on with the tree!


tree bubbles
Soapsuds bubbles at tree base


I was sent photos and sure enough there appeared to be a pile of soap bubbles at the base of the tree!  Diagnostically, I started trying to tease apart what could have possibly happened because trees just do not go around blowing bubbles.  I know this for certain because plants cannot generate enough air pressure to create a bubble!  I then asked about possible soap contamination, like washing cars or detergent spills or even grandkids playing with bubble solution and… no such luck.  In fact, they were quite adamant that no soap or soap-based products were ever near that area or the tree.  So back to the drawing board and time to do some research on possibilities.


tree with bubbles
Those appear to be soap bubbles...


What I found out about rain, trees and bubbles, was simply fascinating!  As it turns out, bubbles piling up at the base of trees, especially after heavy rains, is somewhat commonplace.  During dry periods, there is an accumulation of salts, plant chemicals and other particulates from the air that coat the bark surface.  Soap is essentially a collection of salts and acids.  Think of it like you have all ingredients ready and waiting for making a crude, albeit very simple ‘au natural’ soap solution.  Everything is ready and waiting for the final ingredient—rainwater.


As rainwater trickles down the tree stem or trunk (called stemflow), it collects deposited dust particles (i.e. salts) and plant residues (i.e. acids) that have accumulated on the bark surfaces.  Bubbles are formed through the process of “stemflow mixing”.  As this dissolved, simple soap solution flows down the trunk, it encounters barriers and bumps, like bark plates, furrows, and ridges.  The solution is then tumbled, mixed and aerified, during its downward flow to the ground, generating the bubbles or soapsuds, which collect at the tree base.  Occasionally, a light coating of foam may even be visible higher up on the tree trunk.  Stemflow mixing has no known deleterious effect on tree health.


Tree suds can happen in all types of trees and has been observed occurring in all continents where trees grow.  There is absolutely no need for worry, if foam forms on your trees during or after heavy rains.  In fact, it is an awesome natural phenomenon, so just sit back, relax, enjoy the rain and the bubbles!