If your grow kit is not growing, the cause is almost always one of four things: it is too cold, it is not getting enough fresh air, the humidity is too low, or you simply need to wait longer. All four are fixable. The one problem that is not fixable is contamination, and knowing how to tell the difference between healthy white mycelium and a mould that means the kit has to go is the most important skill in this guide. Here is how to diagnose what is wrong and what to do about it.
In this article
- First, is it actually a problem?
- Quick diagnosis table
- Temperature
- Humidity and misting
- Fresh air exchange
- Contamination: how to recognise it
- When to bin a kit
- Frequently asked questions
First, is it actually a problem?
Before you change anything, check the calendar. The single most common false alarm is impatience. A kit can sit for one to two weeks looking like nothing is happening before the first pins appear. If you are only a few days in and the surface still looks like plain white mycelium, that is normal. Keep up the daily care and wait. If you are past two weeks with the right conditions and still nothing, then it is time to work through the causes below. For the full method, see our step-by-step grow kit guide.
Quick diagnosis table
| Symptom | Likely cause | Fix |
|---|---|---|
| No pins after 2 weeks | Too cold, or too little fresh air | Move somewhere warmer, fan the bag more often |
| Substrate drying out | Humidity too low | Mist the bag walls, not the substrate |
| Long thin stems, tiny caps | Not enough fresh air | Open and fan the bag more, twice daily |
| Pins forming then aborting | Humidity swings or dry air | Steadier misting, keep the bag closed between airings |
| Green, blue, grey, black or pink patches | Contamination | Do not eat. Bin the kit safely (see below) |
| Sour, rotten or ammonia smell | Bacterial contamination | Bin the kit |
Magic Mushroom Grow Kits
Temperature
Mushrooms are fussy about warmth. The sweet spot is 21 to 24 degrees Celsius. Below about 18 degrees, growth slows to a crawl and can stall completely, which is why kits placed on cold windowsills or in unheated rooms so often seem dead. The fix is simple: move the kit somewhere consistently warm, away from draughts and cold glass. Avoid the opposite mistake too, since heat above the high twenties stresses the kit and invites mould.
Humidity and misting
Mushrooms are mostly water and need a very humid microclimate to form. If the inside of the grow bag looks dry, mist the walls of the bag with fresh water, not the substrate itself, which should never be soaked. If pins keep forming and then shrivelling, the usual culprit is humidity that swings up and down, so aim for steady dampness rather than alternating soaking and drying.
Fresh air exchange
This is the step beginners most often skip, and it matters more than almost anything else. Mushrooms need the stale, carbon-dioxide-rich air swapped for fresh air to trigger and shape fruiting. Too little fresh air gives you long stringy stems with tiny caps, or no pins at all. Open the bag once or twice a day, fan it a few times, and close it again. This one habit fixes a surprising number of stalled kits.
Contamination: how to recognise it
Healthy mycelium is white, sometimes with a bluish bruise where it has been touched, which is normal. Contamination looks and smells wrong. Learn the warning signs:
Green or blue-green fuzzy or powdery patches are the most common contaminant, usually a mould called Trichoderma, and they spread fast. Black, grey, pink or yellow slimy or fuzzy growth is also contamination. A grey cobweb-like growth that spreads quickly across the surface is cobweb mould. Any sour, rotten, or ammonia-like smell points to bacterial contamination. Healthy kits smell earthy and pleasant, like fresh mushrooms.
Never eat mushrooms from a contaminated kit. If you see coloured mould or smell rot, do not harvest and do not consume anything from that kit, even parts that look clean. Contamination can make you seriously ill. When in doubt, throw it out.
Contamination almost always enters through dirty hands, dirty water or airborne dust. It is not usually something you can cure once it takes hold. To understand what healthy colonisation should look like in the first place, our mycelium explainer is worth a read.
When to bin a kit and start again
Bin the kit if you see any coloured mould, cobweb growth, or a foul smell. To dispose of it safely, seal the whole thing in a bag before it releases more spores, and put it in the outside bin. Wash your hands and the surface it stood on. It is disappointing, but a contaminated kit will never recover, and trying to save it risks spreading spores to a fresh one.
If the kit simply stalled without contamination, it has not failed, it just needs better conditions. Warm it up, air it more, keep the humidity steady, and give it time. A forgiving strain helps too, which is why the Golden Teacher grow kit is the recommended starting point.
Starting fresh?
Our grow kits arrive fully colonised and lab-checked, ready to fruit, with discreet EU delivery. Golden Teacher is the most forgiving place to begin again.
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Frequently asked questions
Why is my grow kit not pinning?
Usually too little fresh air, humidity that is too low, or a temperature that is too cold. Air the bag more often, mist the walls, move it somewhere warm, and give it time. Pins can take one to two weeks to appear.
How do I know if my grow kit is contaminated?
Look for green, blue, black, grey or pink mould, cobweb-like growth, or a sour or rotten smell. Healthy mycelium is white and smells earthy. Coloured mould or a bad smell means the kit is contaminated.
Can I still eat mushrooms from a contaminated kit?
No. Never consume anything from a kit showing mould or a foul smell, even the parts that look clean. Dispose of the whole kit safely.
My mushrooms have long thin stems and tiny caps. Why?
That is a classic sign of too little fresh air exchange. Open and fan the grow bag more often, twice a day, and the next flush should come out better formed.
Is a blue colour on the mycelium bad?
No. A bluish tinge where mycelium or a mushroom has been touched or bruised is normal and harmless. It is coloured, fuzzy or powdery mould that signals contamination, not bruising.
How long should I wait before deciding a kit has failed?
Give it at least two weeks of good conditions before worrying, and only give up entirely if you see contamination. A stalled but clean kit can still fruit once conditions improve.
