Understanding Contamination: The #1 Reason Grows Fail

Contamination is every grower’s worst nightmare — and whether you're just getting started or have dozens of harvests under your belt, it's the one factor that can ruin an entire batch overnight. But the good news? Contamination is almost always preventable.

What Is Contamination?

In mushroom cultivation, contamination refers to the unwanted growth of molds, bacteria, or yeast in your substrate, grain, or liquid cultures. These invaders compete with your mycelium for nutrients — and often win.

• Green mold (Trichoderma): Most common — fast-growing, bright green patches.
• Bacterial contamination: Wet spots, sour smells, slimy textures in grain.
• Yeast or pink mold: Discoloration, unusual smells, often appears in LC jars.

Even a tiny lapse in sterile technique — or low-quality materials — can invite contaminants into your grow. That’s why prevention is more important than treatment.

How to Prevent It

Contamination prevention starts long before you see white mycelium. It’s built into every step — from preparation to inoculation.

• Always sterilize tools and surfaces with 70% isopropyl alcohol.
• Use a still air box (SAB) or flow hood for inoculations.
• Use proper hydration: too wet = bacteria heaven.
• Only use clean, proven genetics and substrates.
• Store your grain and LC at appropriate temperatures (21–24°C).

In fact, when growers use our substrates and genetics, contamination rates are often zero. That’s because we prepare everything with lab-level sterility, pressure-sterilized and batch-tested before shipping.

Signs You've Got Contamination

• Bright green, pink, or black patches in the grain or bag.
• Strong unpleasant odors (sour, rot, or feet-like).
• Slow or stalled growth while other parts flourish.
• Overly wet or slimy substrate.

When in doubt, throw it out. Contamination spreads — and saving a bag almost never works.

Final Thoughts

Contamination can be intimidating — but it’s not mysterious. Most cases come down to one of three things: unclean tools, unclean air, or unclean ingredients. Eliminate those, and you’re already ahead of the game.