Most mushroom growing problems come down to just a few things: patience, temperature, and cleanliness. Slow growth almost always means your kit is too cold — aim for 24–26°C. Weird colours are usually either harmless (cream patches, blue bruising) or a sign of contamination (green, black, pink, slimy, or bad-smelling). Small or sparse mushrooms are usually down to genetics, not anything you did wrong. This guide walks through the 8 most common problems beginners run into, what’s actually going on, and exactly what to do about it.
Growing mushrooms can feel a bit nerve-wracking the first time. You’ve set everything up, you’re checking your kit constantly, and you’re not totally sure if what you’re seeing is normal or a disaster waiting to happen.
Here’s the good news: almost every “problem” beginners worry about turns out to be either completely normal, or an easy fix once you know what’s going on. This guide goes through the most common issues one by one, explains what’s actually happening in plain English, and tells you exactly what to do.
1. Nothing’s Happening Yet
2. Growth Is Slow or Stalled
3. Water Drops Inside the Bag
4. Weird Colours Appearing
5. Blue Marks on the Mycelium
6. Mushrooms Growing Oddly
7. Tub Keeps Getting Contaminated
8. Mushrooms Are Small or Few
1. “Nothing’s Happening Yet” — The Waiting Game
I’ve started my kit but I can’t see anything growing
This is the most common thing new growers worry about — and it’s almost always nothing to worry about. Mycelium (the white, thread-like stuff that grows before mushrooms appear) doesn’t show up instantly. It needs time to “wake up” and start spreading.
✅ The Golden Rule
Don’t keep opening your kit to check on it. Every time you open it, you let in fresh air that could carry unwanted mould or bacteria. Just leave it somewhere warm and check once a day through the bag or container.
2. Growth Is Slow or Has Stalled
My mycelium started growing but it’s really slow, or it’s stopped
This one comes down to a single word: temperature. Mycelium is alive, and like most living things, it’s much more active when it’s warm. Cold = slow. Warm (but not too warm) = fast.
🔍 Most Likely Cause
Your kit is sitting somewhere too cold — maybe a cool room, a windowsill, or anywhere below about 20°C. Mycelium just doesn’t grow quickly in the cold.
✅ The Fix
Move your kit somewhere warmer — ideally 24–26°C. A warm shelf, on top of a fridge, or using a heat mat underneath the kit all work well.
⚠️ Don’t Go Too Hot
It’s tempting to think “warmer = faster, so let’s crank it up” — but don’t go above 27°C. Above that, mould and bacteria start growing faster too, and they can outcompete your mycelium. There’s a sweet spot, and 24–26°C is it.
3. Water Droplets Inside the Bag
There’s water building up on the inside of my grow bag
As mycelium grows, it actually produces a small amount of its own heat — like a tiny engine running. This makes the inside of your substrate slightly warmer than the room around it. When that warm, moist air hits the cooler plastic of the bag, it turns into water droplets — exactly like condensation on a cold drink can.
✅ This Is Normal And Healthy
A few small droplets here and there means your mycelium is alive and working hard. Nothing to do — just leave it alone.
⚠️ But Watch Out For This
If you see pools of water building up, or the substrate looks slimy or sludgy rather than just damp, that’s a different story — it could be a sign of contamination. Check the next section on weird colours and smells.
4. Weird Colours Appearing
My mycelium isn’t white anymore — should I be worried?
This depends entirely on which colour you’re seeing. Some colour changes are completely harmless. Others mean it’s game over for that kit. Here’s how to tell them apart.
| Colour You See | What’s Going On | Status |
|---|---|---|
| Creamy yellow | Mature mycelium releasing natural substances. More common if it’s been a bit too warm. | Usually fine |
| Blue / grey-blue patches | Bruising from being touched, moved, or knocked. Not contamination. | Normal |
| Green | Almost always Trichoderma — a fast-spreading green mould. | Contaminated |
| Black | A type of mould contamination, often spreads in patches. | Contaminated |
| Pink or red | A fast-spreading mould, sometimes called bread mould. | Contaminated |
| Slimy + bad smell | Bacterial contamination — usually from too much moisture. | Contaminated |
⚠️ If It’s Contaminated
Sadly, once mould or bacteria takes hold, there’s no saving that kit. The safest thing to do is seal it up and bin it (don’t open it indoors — you don’t want spores spreading around your house) and have a think about what might have let it in. The most common causes are too much moisture or letting unclean air in.
5. Blue Marks on the Mycelium
Part of my mycelium has gone blue — is this mould?
Almost certainly not. Blue or grey-blue patches on white mycelium are usually just bruising — the mycelium’s version of a bruise on your arm after bumping into something. It happens when the mycelium gets pressed, knocked, or moved around (for example, against the side of a jar or bag).
The good news is that bruised mycelium isn’t damaged in any serious way and will usually look normal again pretty quickly.
How to Check: The Cotton Bud Test
- Gently rub a clean cotton bud over the blue patch
- Look at the tip of the cotton bud
- Nothing transferred? It’s bruising — totally fine, leave it alone
- Colour transferred onto the bud? That’s mould, not bruising — see the section above on contamination
✅ Simple Fix
If it is just bruising, the best thing to do is simply handle and move your kit less. The mycelium will recover on its own.
🤔 Quick Recap: Bruising vs Contamination
Flat blue or grey-blue patches. Happens after the kit’s been touched or moved. Cotton bud test: nothing transfers. No action needed.
Green, black, pink, or fuzzy patches — often with a slimy texture or bad smell. Cotton bud test: colour transfers. Bin the kit.
6. Mushrooms Are Growing — But Behaving Oddly
My mushrooms aren’t growing all at the same time, or the substrate looks dry after picking
How your mushrooms grow and group together really comes down to genetics — and that’s completely out of your control. Some kits will produce all their mushrooms in one neat “wave” (called a flush), all roughly the same size and ready to pick together. Others will grow more randomly, with mushrooms popping up at different times.
What to Do in Each Case
- Growing all together (uniform flush): Wait until most of them look ready, then pick the whole batch at once. After that, get the substrate ready for the next flush.
- Growing randomly (sporadic): Just pick each mushroom as it becomes ready, rather than waiting for the others to catch up.
After Your First Flush: Rehydrating
Once you’ve picked your first batch of mushrooms, the substrate often looks a bit dry. This is totally normal — growing mushrooms uses up a lot of water. To get ready for the next flush, give the substrate a good soaking using a spray bottle or mister. Don’t be shy with it — really mist it well so the substrate can soak the moisture back up.
✅ Patience Pays Off
Most kits can produce 2–4 flushes total. Each one is usually a bit smaller than the last, but it’s well worth rehydrating and waiting for the extra flushes — you’re basically getting multiple harvests for free.
7. My Tub Keeps Getting Contaminated After Spawning
Every time I mix my grain spawn into the bulk substrate, the tub ends up contaminated
If contamination shows up right around the first flush — either just before or just after — the problem almost always traces back to one moment: when you mixed the grain spawn into the substrate (this step is called spawning). That’s the point where everything gets opened up and mixed by hand, which means it’s also the point where unwanted mould or bacteria has the best chance to sneak in.
Where Things Usually Go Wrong
🔍 Common Causes
A dirty work surface, dust or drafts in the room, dirty hands, or storing the tub somewhere with lots of airborne particles (like on the floor).
✅ How to Fix It
Clean your space properly, wear gloves, sanitise your hands, and store finished tubs up off the floor.
Your Spawning Checklist
- Pick a clean spot — a kitchen surface wiped down with disinfectant works well. Avoid anywhere with a draught (open windows, doors, fans)
- Wear gloves and clean your hands with isopropyl alcohol (also called rubbing alcohol) before you start
- Work quickly but carefully — the less time everything’s open to the air, the better
- Store the finished tub off the floor — ideally on a shelf, a few feet up. Most mould spores and dust float around near floor level, so storing tubs low means they sit in dirtier air
ℹ️ Why Height Matters
It sounds like a small detail, but it makes a real difference. Air near the floor carries more dust, fibres, and airborne spores than air a few feet up. Simply moving your tubs onto a shelf can noticeably cut down contamination rates.
8. My Mushrooms Are Small or There Aren’t Many of Them
I did everything right, but my mushrooms came out small or sparse
This is the one that surprises people most. If your mushrooms are small, thin, or there just aren’t many of them — it’s usually not because of anything you did. It’s down to genetics.
Think About It Like People
Within any group of people, you’ll find tall and short, big and small, strong and not-so-strong. That’s just natural variation caused by genetics — the biological “instructions” each person is born with. Fungi work exactly the same way. Some mycelium is naturally going to produce bigger, thicker, more abundant mushrooms than others — and it’s down to the genetic code inside it, not how well you looked after it.
Why Spores Are a Bit Like a Lottery
If you started your grow using a spore syringe, here’s what’s actually happening at a microscopic level: the spores “wake up” and grow tiny threads. Threads from different spores join together to form mycelium — and that new mycelium ends up with a random mix of genetics from its “parents.” It’s a bit like how siblings can look quite different from each other, even with the same parents.
This means there’s no way to guarantee in advance whether the mycelium that grows will have “great mushroom” genetics or “just okay” genetics. Most of the time it’ll be fine — but sometimes you’ll get a smaller harvest purely by chance.
🎲 Spore Syringe
Random genetic mix every time. Usually good results, but no guarantees — a bit of luck is involved.
🎯 Liquid Culture
Already-grown mycelium with genetics that have been specifically chosen for good size and yield. Far more predictable, consistent results.
✅ Want More Predictable Results?
If big, reliable harvests matter to you, starting with liquid culture instead of spores removes a lot of the guesswork — because the genetics have already been picked out for good growth, rather than being random.
Got Everything You Need to Get Started?
Tripping Store stocks spore syringes, grow bags, substrates, and heat mats — everything you need to get growing with confidence.
Frequently Asked Questions
Most people see the first signs of white, fuzzy growth (called colonisation) after about 5 days. But it’s completely normal for this to take up to 2–3 weeks, especially if you started with spores rather than liquid culture. If you’ve waited more than 3 weeks with no change at all, it’s worth checking your temperature — it’s probably too cold.
Aim for 24–26°C during the growing (colonisation) stage. This is the sweet spot where mycelium grows quickly without giving competing moulds and bacteria an advantage. Avoid going above 27°C — temperatures higher than that start to favour contamination over your mushroom mycelium.
Yes, a small amount of condensation is completely normal and is actually a good sign — it means your mycelium is alive and producing its own heat as it grows. Only worry if you see actual pools of water forming, or if the substrate looks slimy or sludgy rather than just slightly damp, as that can be a sign of contamination.
Use the cotton bud test. Gently rub a clean cotton bud over the discoloured area and check the tip. If nothing transfers onto the cotton bud, it’s just bruising — completely harmless and the mycelium will recover on its own. If colour does transfer onto the cotton bud, that’s mould, and the kit should be thrown away. Blue or grey-blue colours are almost always bruising; green, black, or pink are almost always contamination.
A creamy yellow colour appearing on mature, well-established mycelium is usually completely normal. It happens when the mycelium releases certain natural substances as it matures, and tends to be more common when temperatures have been a little on the warm side. If you’re seeing this a lot, try keeping things slightly cooler — but on its own, yellowing isn’t a sign of a problem.
Whether mushrooms grow all together in one neat batch (a flush) or pop up more randomly over time depends mainly on genetics — it’s not something you’re doing wrong. If they’re growing together, wait until most are ready and harvest the whole batch at once. If they’re growing sporadically, just pick each mushroom as it matures rather than waiting for the rest.
This points to contamination getting in during the spawning step — when you mix the colonised grain into the bulk substrate. This is the moment everything is opened up and handled, giving mould or bacteria the best chance to get in. Reduce the risk by working in a clean area with no draughts, wearing gloves, sanitising your hands with isopropyl alcohol, and storing finished tubs on a shelf rather than the floor, since floor-level air carries more airborne contaminants.
Mushroom size and yield are mostly down to genetics, not growing technique. Just like people vary naturally in height and build, different mycelium will naturally produce different sized mushrooms. If you grew from a spore syringe, the resulting mycelium has a random genetic mix, so results can vary. If consistent, larger harvests matter to you, using a liquid culture — where the genetics have already been selected for good growth — gives more predictable results than starting from spores.
