A yellow, foam-like growth has suddenly appeared in my mulched perennial bed. What is it and will it harm my plants?
The growth in your perennial bed is probably a slime mold. Slime molds are types of fungi. Slime molds feed on bacteria and other organisms in the mulch. They do not harm plants.
Slime molds are usually a temporary nuisance. Within a few days, slime molds typically dry up and turn into white, powdery masses. Most individuals simply let the slime molds dry up and fade away. However, the slime molds can be scooped up and discarded if you find them objectionable.