Understanding Colonization and Contamination

Colonization is the longest silence in a grow, and the stage where most problems either appear or are prevented. Learning to read it is the single most valuable skill a grower develops.

Healthy mycelium, described

Healthy mycelium is white, and it looks like a dense mat of fine threads rather than a powder. It advances in an even front from the inoculation point and has a slightly furry, pulled-cotton texture at the leading edge.

Some species throw faint yellowish or brownish tints as they age, which is normal metabolic byproduct. Patches that are bright white but lumpy and powdery are usually not mycelium at all.

Reading the warning signs

Contamination announces itself in colour and smell. Green, black, pink, or bright orange growth is mould, without exception. Sour, sweet, or fermented smells mean bacteria. Wet, slimy grain means the substrate is breaking down.

Colour is the fastest signal. Mycelium has essentially one colour, and anything else is a problem.

• Green or black — Trichoderma or Aspergillus
• Pink or orange — bacterial or yeast contamination
• Sour smell — bacterial fermentation
• Wet, slimy grain — substrate breakdown

What to do when you find it

Act immediately and act locally. Do not open the container indoors. Seal it, carry it outside, and dispose of it. If the contamination is confined to one corner of a large bag and the rest is healthy, some growers cut the block apart — but for a beginner, discarding is almost always the better call.

Then find the cause. Contamination during colonization usually traces to incomplete sterilisation, wet substrate, or a lapse in sterile technique during inoculation.

Putting it into practice

Ideas are cheap; the sequence is what makes them work. The three habits below are the ones that separate growers who repeat their results from growers who keep starting over.

Common questions