Slime mold is a brightly colored organism that spreads across wood mulches during periods when temperatures are warm and humidity is high. Most people report seeing patched or covered areas in mulched beds that appear spongy and sometimes cauliflower like. 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.
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 cauliflower-like blobs in the garden.