During the recent rains, as I was walking through my backyard, I noticed white foam at the base of our pine tree and wondered why it was there. Was it an indication of something harmful, or was my tree in a party mood and blowing bubbles to celebrate? 

The reason trees are foaming 

During dry periods, an assortment of particulates, plant chemicals, and air pollutants accumulate on the bark surface of trees. When rain collects on a tree’s canopy, these ingredients mix as they flow down the trunk and concentrate toward the base of the tree. The mixture of rainwater and these chemicals results in the formation of a crude soap. And as the mixture flows over the tree bark furrows, the turbulence stirs up the soap and creates a frothy white foam. Much like car tires creating white foam during the first rains of the season on roadways.

This smooth-barked crape myrtle is too small and too smooth to collect enough chemicals to create soap.

Do all trees create soap?

Theoretically, all trees could create foam, but the best trees to find foam on are larger diameter trees with plenty of deep bark ridges. Large trees create a large surface area for the accumulation of soap ingredients. The rough, furrowed bark of pine trees helps to mix the chemicals with rainwater to create the soap. Large trees with smooth bark, such as Coast Live oaks, maples and Crape myrtles, rinse off the soap without creating any bubbles.

Do trees create “soap bubbles” every time it rains?

No, they don’t. The best time to see this process is after our hot, dry summer and during an extended period of rainfall. The rain we had December 9-12, 2022, was a perfect set-up for the creation of tree soap. Obviously, it had been several months without significant rain, which allowed for the build-up of chemicals on the tree trunk. The rain was sufficient enough over a couple of days to wash down the entire trunk of the pine and adequately mix to create the soap bubbles at the bottom.

Is this “soap” mixture harmful to my tree?

No, it is not. The chemicals and particulates accumulate on the outside of the trunk and do not enter the vascular system of the tree. Even if the “soap” gained access through a wound on the tree, the chemicals are not toxic enough to do any damage.

And studies have shown that annual nutrient returns to forest soils for elements such as potassium and sulfur are predominantly via throughfall and stem flow during the rainy season instead of the decomposition of leaf litter. So the appearance of foam at the base of your tree is a good thing!

However, if you see anything unusual appearing on or near your tree and you are unsure about its significance, do not hesitate to call our office and set up an appointment with one of our arborists to check the health of your trees.