Yellow Slime Mold

What you have seen is a very interesting organism called a “slime mold”. It is not a fungus but more like a protozoan and is a natural component of the mulch environment. Spores germinate into small (microscopic) organisms that move around, feeding on decomposing organic matter – the bark mulch. These growths suddenly show up after heavy rains or after watering plants in warm, muggy weather – even in the best of gardens! These fungi are not harmful to landscape plants & no known health hazards are associated with them unless they are eaten. Chemicals do not provide control. Instead, break up the spore masses by vigorously raking or hosing down with a stream of water. Slime molds dry out and turn brown in about 2 weeks and will disappear with hot, dry weather.

More reading on yellow slime mold:

Colorado State Cooperative Extension

Texas Cooperative Extension