What to Know About Slime Mold on Grass

Slime molds, also known as myxomycetes, are fascinating organisms that can sometimes appear in lawns and landscapes. Though slime molds thrive outdoors, they rarely pose a threat to grass health. Understanding their life cycle and ecological roles can help discern when treatment or removal may be warranted.

What Are Slime Molds?

Slime molds are not actually fungi or mold at all. They are protists – primitive organisms that have characteristics of animals, plants, and fungi. With over 900 identified species, myxomycetes have complex life cycles. They move and feed like animals when in active plasmodial or amoeboid stages. They also grow and form spore-producing fruiting bodies reminiscent of fungi.

In their plasmodial stage, slime molds ooze over surfaces engulfing food sources. Their bright colors come from pigments in their protoplasm. The “slime” moniker comes from their moist, mucoid appearance during motion. When ready to spore or environmental conditions turn harsh, they transform into fruiting structures.

Slime molds frequent damp shaded habitats worldwide. These primitive organisms play pivotal roles in decomposition and soil ecology. Though slime molds on lawns or landscape plants can appear worrisome, they typically do not harm live plants. Their presence often indicates organic mulches or soils rich in microbes, fungi and decomposition.

Life Stages of a Slime Mold

Slime molds have complex life cycles with up to 4 different body forms. The vegetative stages actively hunt bacteria, yeasts and fungi as food sources. When ready to reproduce, they form reproductive fruiting structures.

Plasmodial or Vegetative Stage

  • Slime molds spend the majority of their lives in the vegetative plasmodial stage.
  • The plasmodium oozes over surfaces engulfing food particles.
  • Plasmodia can be small, or grow to expansive nets covering several feet.
  • Vegetative slime molds move slowly, only a few inches per hour. They thrive in damp, shady areas.
  • Plasmodial slime molds are brightly colored, usually yellow, orange, or red.
  • Vegetative stages may persist for weeks or months before forming spores.

Amoeboid Stage

  • Some slime molds, like Physarum, have an amoeboid trophic stage.
  • Amoeboid cells hunt and ingest food individually.
  • They later aggregate to form a plasmodium.
  • Amoeboid slime molds multiply rapidly when food is abundant.

Fruiting Stage

  • When ready to reproduce, slime molds enter the fruiting stage and form sporangia.
  • Sporangia rise up on stalks or tree-like structures to better disperse spores.
  • Fruiting bodies may be minute, or reach sizes over several inches.
  • Shapes and colors are highly variable between slime mold species.
  • In dry weather, fruiting usually occurs after nighttime rains.

Spore Dispersal

  • Fruiting bodies produce haploid spores through meiosis.
  • Spores disperse via wind, rain-splash or insects.
  • Spores germinate under suitable conditions, releasing free-living amoeboid cells.
  • Amoeboid cells multiply and later mass together as plasmodia or slime.

The spores are the survival and propagation units. Plasmodia and fruiting bodies die off after spore release. The spores can lie dormant for years awaiting ideal germination conditions.

Are Slime Molds Harmful to Grass or Plants?

Slime molds thriving in lawns or gardens seldom harm established vegetation. As primitive organisms, they cannot infect live plant tissue or parasitize healthy plants and grass. However, conditions prompting their germination could stress sensitive plants.

Slime Molds Do Not Kill Grass

The moist thin layer of slime molds oozing over grass is harmless. Plasmodial slime molds simply engulf microbes, organic debris and dead plant material for food. Healthy grass tissue is unaffected. Starved of sunlight under the slime layer, grass blades may weaken and collapse. But the grass crown and roots remain safely intact underground, rapidly regrowing after the slime mold dies.

Potential Harm to Seedlings

Expanding slime molds may overtake small seedlings in greenhouses, nurseries or after direct seeding. The slime coating can cut off sunlight or physically uproot tiny fragile plants. But established plants and lawns can withstand temporary plasmodial slime layers without harm.

Environmental Factors Are the Primary Cause

While slime molds do not kill plants directly, their presence signifies environmental conditions that may detrimentally impact vegetation. Excess moisture permitting explosive slime mold growth deprives grass roots of oxygen. Nutrient deficiencies or imbalances promoting slime molds can stress sensitive plants. Removal of slime molds may be warranted, but correcting underlying conditions is key.

Why Do Slime Molds Populate Lawns and Landscapes?

Slime molds are not random invaders. Their life cycles require very specific habitat parameters. Their presence provides clues into landscape and soil health. Key factors prompting slime mold blooms in turfgrass include:

Moist Shady Conditions

  • Slime molds thrive in damp shady areas, under trees or dense canopies.
  • Irrigation spraying onto foliage prolongs moisture.
  • Poor drainage or compacted soils prevent drying.
  • Mulches or heavy thatch hold moisture near the soil surface.

High Organic Content

  • Slime molds feed on bacteria, fungi and decaying matter.
  • Compost, manure mulches and rich organic soils support their growth.
  • Excess Nitrogen fertilization increases microbial activity.

Low pH Acidic Soils

  • Slime molds favor acidic conditions below pH 6.5.
  • Acidic soils have less bacterial competition.
  • Acidic conditions increase solubility of nutrients from organic matter.

Oxygen Deprivation

  • Saturated soils are low in oxygen due to waterlogged conditions.
  • Compaction reduces soil air pockets.
  • Slime molds are tolerant of low oxygen, unlike grass roots.

Significance of Slime Mold Bloom in Landscapes

A slime mold outbreak often coincides with environmental stresses for turfgrass. While slime molds themselves are harmless, their presence warrants investigation into underlying causes.

High humidity, shade, and acidic soils favor slime molds over turfgrass.

Corrective actions may include:

  • Improving air circulation and light penetration through selective pruning.
  • Modifying irrigation to allow soils to dry between waterings.
  • Reducing nitrogen inputs and soil compaction.
  • Topdressing with lime or alkaline materials to raise pH.
  • Aerating soils to increase oxygen.

Slime molds indicate rich organic soils.


  • Reducing thick organic mulches providing food sources.
  • Allowing mulch to decompose before re-applying.
  • Testing and correcting potential nutrient excesses or deficiencies.

Explosive slime mold growth denotes imbalance.

  • A healthy diverse soil microbiome keeps slime molds in check.
  • An unstable soil food web allows rapid slime mold expansion.
  • Judicious fertilization and organic practices promote biological diversity and plant health.

Removal and Treatment of Slime Molds

Though generally harmless, slime molds may require removal for aesthetic reasons or to protect seedlings. Careful methods are needed to avoid harming beneficial soil life.

Manual Removal

Gently hose or wipe plasmodial slime molds off foliage or hardscapes. Take care to avoid spreading spores. For slimes on lawns mow and bag clippings immediately before spore formation.

Modifying Habitat

Improve drainage and light penetration. Allow soils to dry between irrigations. Discontinue high nitrogen fertilization and dense organic mulches promoting decay.

Chemical Treatment

Mild biodegradable detergents can dissolve slime membranes. Hydrogen peroxide rapidly eliminates slime molds. Avoid persistent chemicals lethal to vital soil biota. Always follow label safety directions.

Biological Control

Beneficial bacteria like Bacillus subtilis help break down slime mold tissues. Bulk populations of beneficial organisms via composts, compost teas, or inoculants. Ensure adequate soil oxygen levels for their activity.


In most cases, the presence of slime molds does not justify control efforts. They die back naturally in dry weather. Tolerating them avoids disrupting soil life. Focus instead on addressing underlying conditions promoting their survival.

When Should Slime Molds Cause Concern?

Most slime mold outbreaks quickly fade without intervention. However, some situations may warrant action to remove or reduce their populations:

Newly Seeded Lawns or Seedlings

Slime layers can smother and uproot tender young shoots. Gently wash slimes off seedling foliage. Allow soils to dry between irrigation cycles.

Prior to Important Events

Eliminate unsightly slimes marring lawns for special gatherings. Wash off with gentle detergents and resume normal irrigation schedules.

Recurring Expansive Growth

Extensive repeating slime mold outbreaks indicate soil imbalances. Improve drainage, aerate compacted areas and adjust organic inputs and fertilization.

Change in Ecosystem

A sudden slime mold bloom after site changes like grading or new plantings denotes a biological imbalance. Restore diverse soil life through applications of compost and compost tea.

Highly Manicured Areas

In ornamental gardens, patios or golf greens, slime molds may necessitate treatment. Use least toxic methods like hosing and beneficial organisms.

Coexistence with Slime Molds

Trying to permanently eliminate slime molds is neither feasible nor ecologically sound. Avoidance of harsh chemicals prevents damage to vital soil organisms that keep slime molds in check and cycles nutrients.

Slime molds naturally decline as conditions dry. Improving cultural practices to favor grass over slime molds restores biological balance. With informed adjustments, landscapes can support the natural biodiversity vital for plant and soil health. A live-and-let live approach allows peaceful coexistence with slime molds.

Frequently Asked Questions About Slime Molds on Lawns

Can slime molds kill my lawn or grass?

No, slime molds do not directly harm established lawns or turfgrass. Their presence indicates excess moisture or acidic conditions favoring slime molds over grass. Correct underlying environmental issues to restore vigor to the lawn.

Should I worry about slime molds taking over my lawn?

Most slime mold outbreaks are temporary and recede on their own. Recurring extensive blooms indicate biological imbalances correctable through cultural practices. Healthy soils with good drainage, oxygenation and pH support diverse soil life that keep slime molds in check.

How do I get rid of slime mold on my lawn?

Gently hose slime molds off grass blades, bag clippings after mowing, or use a soft brush. Avoid spreading spores. Correct conditions like poor drainage, low pH, compaction and excess nitrogen favoring slime molds. Apply lime, aerate, adjust watering and fertilization to favor grass growth over slime molds.

Is slime mold bad for my lawn?

Excessive slime mold growth is symptomatic of underlying issues rather than causing harm itself. Slime molds indicate poorly drained acidic soils with unbalanced nutrients andbiology. Correct these conditions through integrated best practices to improve turfgrass health and vigor.

Should I rake slime mold off my lawn?

Gently hosing or wiping slime molds off grass blades is preferable to raking. Raking risks spreading spores and damages grass blades under the slime layer. Mow and bag slime mold covered grass before spore formation. Proper conditions will allow grass to regrow after slime molds naturally die back.

How do I stop slime mold from coming back in my lawn?

The key is addressing the underlying factors promoting slime mold growth. Improve drainage, reduce compaction, adjust irrigation to allow drying. Raise pH above 6.5 with lime applications. Correct nutrient excesses/deficiencies and disproportionate organic matter levels favoring slime molds. Promote biological diversity through composts and compost tea applications.


Slime molds are fascinating primitive organisms, but their presence in lawns often sparks alarm. Although slime layers can detract from turfgrass aesthetic appeal, they do not directly harm established vegetation. Slime mold growth points to excesses of shade, moisture and acidity favoring their development over grass. With adjustments to cultural practices that improve sunlight, drainage, oxygenation and soil chemistry balanced turfgrass will regain dominance. An integrated approach promotes healthy biological diversity vital to resilient landscapes. A better understanding of conditions promoting slime molds allows them to be accepted as harmless transient inhabitants of the fascinating miniature world beneath our feet.