Slime Molds

Slime molds are the red-headed stepchildren of the garden world. Not a plant, not an animal, recent research has created more questions than answers about this garden visitor.


This species will appear in your garden. Slime molds do not hurt your crops. Instead, they make nutrients more readily available.

Slime molds help break down leaf litter and mulch (Kate Russell)

Slime molds often appear after it rains. They can be yellow, red, orange, blue, gray, black, clear, beige, or hot pink. They may be flat, lumpy, or a fat, rounded blob. Some slime molds look like thousands of tiny balls, while others look like thready networks. One group is called dog vomit slime mold.


Slime molds usually grow on rotting wood and mulch but can also occur on tree and shrub leaves, berries, succulents, and other plants. The presence of slime mold does not hurt living plant tissue since it doesn’t usually last for very long. At one stage, they look like somebody spilled something foamy on the ground (the infamous dog vomit slime mold). Slightly disturbing, these shiny, lumpy spills move of their own volition, yet they have no brains. At another stage, tiny, individual critters look more like flowering moss, with a small sphere waving around at the end of a stalk. Scientists affectionately refer to slime molds (myxomycetes) as myxos.

Dog vomit slime mold (Kate Russell)

​Slime mold taxonomy

Slime molds are members of the Protista kingdom. More than a billion years old, slime molds are probably life’s first attempt at joining individual cells into complex organisms.


There are two types of slime mold: acellular and cellular. Acellular slime molds have many nuclei (the part of a cell that holds DNA) but only one cell wall during the plasmodium stage. There are 1,000 known species of acellular slime molds. There are only 70 species of cellular slime molds. Each cellular slime mold is an individual cell.

Some slime molds create a fan shape as they seek nourishment (Kate Russell)

Slime mold lifecycle

All slime molds start as spores, but how they reach that point is pretty amazing. Cellular slime molds, as individual cells, emit a chemical that calls other cells to huddle up into a slug-like structure that eventually becomes a stalk rather than a simple mass called a plasmodium. These mindless stalks can spew ammonia to keep competitors away as they generate spores.


These parenting bodies discharge spores, usually into the wind or on a water spray (like fungi). The spores then germinate (like seeds) and then join with other germinated spores to form zygotes (like mammals). These single-celled zygotes feed on decaying wood, fungi, bacteria, and plant material, growing into a plasmodium. These plasmodia can reach several feet in diameter. The record-holding slime mold to date was nearly 60 square feet! They contain no neurons or central nervous system. But they have a surprising ability to solve problems.

There's a lot more going on than meets the eye when it comes to slime molds (Kate Russell)

Crazy experiments with slime molds

We, humans, think that we’re pretty smart. We attribute some level of intelligence to our pets and other favored species. As life forms become more foreign, we are less likely to consider intellect or self-awareness, but this might have to change in light of recent experiments:

• If you chop up a slime mold and spread its pieces out in a maze, the individual pieces will reunite and continue their food search.
• Slime molds will withdraw from dead-end spaces in mazes that contain no food.Slime molds leave behind a mucus trail as a spatial memory to remind themselves of where they have already been (and exhausted food sources).
• They will choose the healthiest foods when offered a selection. (How do they choose without a brain?)
• When provided with food in the same places as primary resources in cities, slime molds have recreated the railway and highway systems of those cities. (Engineers are now considering using this ability of slime molds to help design cities around geographic formations and other limiting factors.
• Experiments involving changing conditions from favorable to unfavorable on a timed schedule have demonstrated that slime molds also have an internal clock.

Slime molds can also be a thing of fleeting beauty (Kate Russell)

Slime molds will not hurt your garden unless they are both thick and persistent. Instead, they help break down dead complex structures into nutrients plants can use. Usually, they are only visible for a short time. If you use a powerful spray of water to eliminate a slime mold, you will spread spores in all directions. If it must go away, dig it up with a pitchfork or shovel and add it to the compost pile. Fixed copper treatments will also eliminate slime molds. But they will reappear in areas with plenty of shade, moisture, and organic material, no matter how often you try.