Mulch white mold
What Is White Mold on Mulch?
White or light-colored growth appearing on wood chip or bark mulch is often linked to a condition known as sour mulch, a problem that can arise from how wood by-products are stored before use.
Wood chips and bark nuggets have long been used as landscape mulches, with many contractors sourcing materials from sawmills, pulping operations, and other wood waste suppliers — all of which involve stockpiling before delivery.
How Sour Mulch Damages Plants
The effects of sour mulch on plants can appear rapidly and be severe. In one documented landscaper experience, plants began to wilt within half an hour of mulch application, and by the following day foliage of tulips, Phlox, Astilbe, and violets had turned white or light tan, as if bleach had been thrown over the plants.
Turf adjacent to the applied mulch was also affected, indicating that the damaging compounds can spread beyond the immediate mulch bed.
Why Stockpiled Wood Mulch Can Turn Problematic
Wood mulch storage techniques significantly affect product quality, and previously stockpiled wood by-products carry a significant, albeit rare, risk of developing toxic properties before they reach a landscape.
While organic mulches normally provide benefits such as stabilizing soil, moderating soil temperature, retarding weed development, and reducing evaporation of soil moisture, improper storage can turn these materials into a hazard rather than a help.
Calculating Mulch Needs Before You Buy
Ordering the right amount of mulch — not too much, not too little — reduces the need to stockpile excess material, which in turn lowers the risk of mulch sitting long enough to sour. Use the mulch calculator at / to estimate exactly how many cubic yards your beds require before placing an order.
Matching your purchase to your actual coverage needs is a straightforward way to keep mulch fresher and minimize the chance of applying a batch that has degraded during storage.
Key takeaways
- White discoloration on mulch can be a sign of sour mulch, which forms during improper stockpile storage and can rapidly damage or kill nearby plants.
- Ordering only the amount of mulch you need right away reduces excess storage time and lowers the risk of sour mulch reaching your landscape beds.
Related tools
Estimate materials with our mulch calculator on MulchCalcs.