slime mold on mulch (16269 bytes)

Slime Mold: That Stuff That Looks Like. . . Well, Dog Vomit

By Nana Mejia, Horticulture Agent, Colorado State University Cooperative Extension

You're out surveying your yard one morning and there it is -- a big, unsavory-looking splotch in your flower bed that looks for all the world as if Fifi threw up all those table scraps you gave her yesterday.

Forget the table scraps. It's probably slime mold, a brightly colored organism that spreads across wood mulches during periods when temperatures are warm and humidity is high.

Most people report seeing an area in mulched beds that appears as though someone has vomited. It really looks bad! Although this can be disturbing to most gardeners, it's no cause for alarm.

Slime molds in the genus Fuligo are organisms that can appear bright yellow to orange, fading to brown and tan as they dry. They pose no threat to plants, animals or children, but they look awful and might be distracting at a garden tour or barbecue.

slime mold up close (8519 bytes)

Slime molds can appear bright yellow to orange

You won't find any miracle cures for slime molds because chemicals do not kill nor eliminate it. In fact, chemicals can do more harm to the applicator and the environment!

The best approach to controlling these unique organisms is to try changing the environment in which they grow. Slime molds and other such organisms will not grow well in dry situations. Little can be done to reduce the amount of rainfall we get, but irrigation systems can be adjusted to keep the mulch from becoming excessively wet on the surface.

Another approach to controlling it is to rake and loosen the mulch chips to break it up. This will let air into the mulch so it can dry.

Wood chip mulches insulate soil from temperature fluctuations, protect trees from string trimmers and mowers and reduce problems of weeds in shrub beds. The slime molds that can grow in wood mulches are classed as 'beneficial' organisms and it's possible that they feed on harmful plant pathogenic fungi found in bark and wood chips, thus controlling the harmful fungi naturally. Therefore, the benefits of slime mold to tree and shrub health outweigh the aesthetic problem of vomit-like blobs in the garden.

Photographs courtesy of Duane Howell.

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Date last revised: 01/05/2010