Mushrooms at the Base of My Tree — Is This Bad?

Fungi reproduce by sending up fruiting bodies — what we call mushrooms — when they have enough biomass to support reproduction. By the time you can see a mushroom, the underlying fungus has been colonizing the tree for years, sometimes a decade. The mushroom is the symptom; the rot is the disease.

The species of mushroom tells us a lot. Honey-colored Armillaria (also called shoestring root rot) is the most common in Spokane and one of the worst. It colonizes the structural roots and the root crown, decomposing the cambium and eventually killing the tree. White rot conks on the trunk (often Ganoderma or Phellinus) indicate active wood decay inside the trunk — the structural strength of the tree is being compromised in real time.

Not all mushrooms mean removal. Some fungi are saprophytic — they decompose dead wood and don't attack living tissue. A mushroom growing on an old stump, on a long-dead branch on the ground, or in the lawn 20 feet from the tree is probably just doing its job in the ecosystem. But mushrooms at the root flare, on the trunk, or in a tight cluster near the base are almost always tied to root or trunk decay.

The diagnostic test is the picture and the location. Photograph the mushrooms close up and from several angles, note the distance from the trunk and the exact attachment point, and call us. We can identify most species visually and tell you whether it's a structural concern or not. For high-stakes trees we sometimes send samples to a lab, but most calls are diagnosable on-site.

If we confirm active root or trunk decay, the conversation shifts to risk. Even a tree with active Armillaria can stand for years if the target is low (back of the property, no structures). Over a roof or driveway, the same tree is a removal within 6–24 months because failure can be sudden and catastrophic. Root-rot trees often look healthy until the day they fall.