You get no single number here. The slime mold lifespan you watch in your mulch and the one printed in a herbarium record are two different things. That blob in your bed is the short part. Utah State University's Intermountain Herbarium reports that some spores sit dormant for 75 years. Wet them after all that time and they still grow.
"That is the same spot," my neighbor told me, thumb out toward the north-side bed. I scraped that patch clean in July. A week of rain later the yellow was back along the same drip line. Dried Physarum polycephalum can be brought back by wetting after drying up, which is why you will see this species called more or less immortal. Water alone does the job.
Three states set what any slime mold lifespan adds up to. The plasmodium is the active feeding stage, one creeping mass that holds many nuclei at once. Dry that mass out or starve it and you get a sclerotium, a hard survival structure. Spores are the third option, and you will never spot a single one in your wood chips.
Plasmodium
- What it is: The active feeding stage, a single spreading mass that carries many nuclei inside one body.
- How long it shows: This is the stage you see in your bed, and it ends fast once fruiting starts.
- What ends it: Drying out or running short of food pushes the mass into its survival form.
Sclerotium
- What it is: The hard survival structure the plasmodium forms, split into cells that hold 0 to 4 nuclei each.
- How long it lasts: The structure rides out a dry spell with no feeding and no movement you could spot.
- What ends it: Water. Wetting a dried mass can put the slime mold back into its feeding stage.
Spore
- What it is: The tough unit the fruiting body makes at the end of the cycle.
- How long it lasts: Dormancy can run 75 years in some species, and the spore still grows after that.
- What ends it: Moisture, which frees the tiny amoeboflagellate cells that start the whole cycle again.
Slime mold dormancy is not sleep the way you picture sleep. The sclerotium packs itself into small cells, each one holding 0 to 4 nuclei, and your bed shows nothing at all while that wait goes on. Spores do the same job in a tougher coat. Both wait on water rather than on your calendar, which is why an answer in days or weeks never quite fits the question you asked.
The full cycle runs in one direction. You start with amoeboflagellates, single cells small enough to swim, and those cells join up and grow into the plasmodium. That mass then puts up a fruiting body you can see without a lens, and the fruiting body makes the spores. The bright yellow you spot in a bed is the start of the fruiting stage, and you will watch the color turn tan or brown as the stage finishes.
Sclerotium revival explains why scraping your bed does so little. You lift out the visible mass, rain returns, and so does the color, often in the same shaded corner where your mulch holds moisture longest. Nothing has to travel in for that to happen. The dried material already sitting on your wood chips is enough.
Do not add these figures up into one number. The 75-year dormancy belongs to spores of certain species, and the wetting revival comes from lab work on one well studied species. In your own beds you should expect a short visible run, then a hard structure or spores you never see, then a return once damp weather comes back. Plan on repeat visits and check the shaded beds first.
Read the full article: Slime Mold: Not a Fungus, Not a Problem
