Not-exactly-dry rot


Sometime last summer, shortly after we’d moved in to the new house and settled our outdoor and garden things (and stuff that needed storing) into the shed, I noticed a fungus beginning to bloom from a crack in the floorboards. I kept meaning to take some photos and get an ID, but never did. This summer it returned, beginning from a slightly different spot in the boards than last year. I watched it grow with some interest, but it was only when it started to swallow the extension cord our lawnmower is plugged in to that I finally went and got my camera.

I sat down with my Lone Pine field guide to Mushrooms of Northeast North America, an excellent guide to fungi, well laid-out with good photos. Some 609 species are covered in the guide, and while this is only a sampling of the different species that occur in the region, the author does make a good effort to provide representation of all of the major groups, such that I can usually at least find a sister species that sets me on the right track, even if I might not find the actual species itself.

However, after several flip-throughs, I was drawing a blank. The only fungus that grew in sheets like this (a growth pattern for which species in the group are called “crust fungi”) that seemed to match was Phlebia radiata, but it wasn’t quite right, and images online didn’t match up. Other Google searches came up blank. Finally, a Facebook friend put me in touch with David Fischer of (he’s also a distinguished mycologist), who was able to put a name to my spreading fungus rather quickly.


It’s Serpula lacrymans, a species of fungus that contributes to dry rot. It is most often found affecting the interior of houses and other structures, and there are many photos online of the fungal growths. I did actually check out “dry rot” as a possibility while I was trying to come up with an ID, but the photos I looked at appeared completely different from the growth in our woodshed. It seems that substrate and location of the fruiting bodies will contribute to their shape and appearance.

The fungus will have a mycelium network (akin to the root system of trees) in the wooden floorboards of the shed; as with many fungi, fruiting bodies will only be put out from certain points of the mycelium. The fruiting bodies (I gather) can survive temperatures as low as 3°C (37°F), so will survive well into the fall here, but will die back from the winter. Indeed, this spring there was no sign of last year’s fungus, but a new one sprang up from the existing mycelium once the weather warmed up.

The fungus is a problem because the mycelium invades the wood and secretes and enzyme that begins to break it down. Though it does typically only invade damp wood, it doesn’t need much moisture in order to grow and survive – perhaps 30 to 40 percent moisture content in its host wood. The floorboards of the old woodshed undoubtedly have that; I don’t think they’re far separated from the ground, and while historically an interior wood stove might have kept the air inside dry, the building hasn’t seen such use in decades. The term “dry rot” doesn’t mean that no moisture is needed or involved, but rather that the fungus typically attacks the drier wood such as that used in construction, rather than the comparatively wet wood (with a relative moisture content of 100%) of newly- or recently-felled trees.


I have to admit that, despite knowing that the fungus is slowly eating away at the floorboards, I’m rather fascinated by it and tempted to let it be and watch it grow and change and take over the shed. Guess maybe I should let the landlord know…