Why Is My Mulch Turning White? (Fungi, Slime Mold, and Wet Piles)
Slime mold and saprophytic fungi
Artillery fungus and siding spores
Prevention: depth, drainage, and refresh
Tools to break up fungal mulch
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True Temper 16-Tine Bow Rake
White fungal mycelium on mulch is often harmless slime mold or artillery fungus — spreading the bed thin with a bow rake exposes it to sun and air so the colony dries out and stops spreading.
Truper Bedding / Manure Fork, 10-Tine
A fork lifts and fluffs packed, wet mulch where fungi thrive — breaking up the anaerobic layer is faster than raking alone when the white growth sits in a thick, soggy pile.
BioAdvanced Fungus Control for Lawns, Ready-to-Spray, 32 oz
If artillery fungus is spotting siding or cars with black spores, a targeted fungicide on the affected bed (after thinning) can knock back persistent colonies that keep reappearing in the same wet corner.
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Related reading
Sour smell instead of white growth? Why does mulch smell so bad. Depth math: mulch depth guide.