Mushroom Filtration Bed

A mushroom filtration bed is a layer of hardwood chips or straw seeded with the wine cap mushroom, a fungus that feeds on woody material. The fungus spreads a dense mat of fine white threads, called mycelium, through the chips. The bed is laid where water leaves a greywater bed, a septic field or a waste lagoon and runs downhill, so the flow passes through the mat - as one bed, a chain of them down a line of channels, or simply as heavily mulched planting. The mat is meant to strip out what the water carries, gut bacteria and heavy metals, and the mushrooms are an edible return from ground that had no other job.

The filtration is the weakest part of the record, and anyone building one should know it. No conservation standard covers the practice, and no extension source measures how much such a bed actually removes from water. What has been measured is the soil side: beds like these suppressed weeds by about 92 percent and made the ground close to 40 percent easier to dig. Deep woodchip does much of that on its own, by depth alone. So the bed is built on the expectation that its output is tested rather than trusted. One assumed to be cleaning something and never checked turns an unknown into a false assurance, which is worse than no bed at all.

Warmth and moisture are operating conditions, not refinements. A mat that dries out stops decomposing and stops doing anything else; a drought halted activity outright in one trial. The fungus also eats its substrate faster than plain mulch rots, settling a bed from about 15 to under 12 cm (6 to under 5 in) in three months, so it is a consumable on a two to three year cycle of fresh chips and spawn rather than a structure that stands. Budget it for the soil it builds, not for the crop. Fruiting starts two to six months after seeding in warm weather, but in one trial only two plots in eighty fruited at all.