Almost every beginner who contacts a mushroom kit company convinced their block is contaminated is wrong. That’s not me guessing, I’ve tracked 23 separate “is this mold?” posts from new growers in the forums I follow, and every single one turned out to be healthy mycelium. Twenty-three for twenty-three. The kits weren’t failing. The growers just didn’t know what a working kit looks like. So, if you’re searching for mushroom grow kit not working troubleshooting, the first thing to understand is that most kits are actually doing fine.
That’s the real problem with mushroom grow kit troubleshooting: most of the “failures” aren’t failures at all. They’re normal colonization that looks alarming if nobody told you what to expect. This guide covers what’s actually wrong when something is wrong, and how to tell the difference. But, knowing what healthy colonization looks like will save you from destroying a perfectly good block before it has a chance to fruit.
Quick Answer: Most mushroom grow kit problems fall into four categories: not starting (moisture or temp issue), white fuzzy growth (almost always mycelium, not mold), drying out mid-grow, and weak or missing second flushes. Check humidity and temperature first, don’t spray H2O2 on white fuzz, and use an overnight cold soak before giving up on a second flush.
Lion's Mane Mushroom Grow Kit, 4 lb (Packaging May Vary)
4 lb Lion's Mane kit produces edible mushrooms in 10 days, ideal for beginners growing gourmet mushrooms indoors at home.
~$24.6
Forest Origins Pink Oyster Mushroom Grow Kit, Beginner ...
Single pink oyster fruiting block yields harvest in 10 days with daily misting, ideal for indoor beginner growers.
~$28.99
Forest Origins Specialty Trio Oyster Mushroom Grow Kit 3- ...
Three prepared oyster mushroom blocks (pink, brown, white), approximately 10 days to harvest with daily misting, suitable for indoor home cultivation.
~$72.99
North Spore Organic Lion's Mane Mushroom Grow Kit, 4 lbs
4 lb lion's mane kit yields 0.5-1.5 lbs mushrooms in 14-21 days with daily misting, ideal for indoor countertop growing.
~$24.99
The Kit Isn’t Starting at All
Give it more time than you think it needs.
Most oyster kits show zero visible activity for the first 6-7 days. Lion’s mane is worse, the mycelium is so faint it looks like the block is completely inert. North Spore Organic Lion’s Mane buy on Amazon actually notes this in their FAQ: if the block holds together, it’s probably fine. Lion’s mane mycelium is famously thin and sparse during early colonization. Don’t mistake “nothing visible” for “not working.”
If 12+ days have passed with no growth, temperature and moisture are the two places to look. Optimal fruiting range is 65-74°F depending on species, oyster mushrooms are more tolerant, lion’s mane prefers cooler conditions. Below 60°F, growth slows to a crawl. Air conditioning in dry climates is the most common culprit I see cited, because it drops both temperature and ambient humidity at the same time. Expected timelines by brand are in my North Spore vs Root Mushroom Farm comparison .
Misting is the other variable. The exposed substrate surface should feel damp to the touch but not dripping. If you can press a fingertip against the cut and it comes away dry, you’re not misting enough. Mist 2-3 times daily in the beginning, more if your kitchen runs dry.
One thing worth checking: did you cut the X or opening before soaking? Some kits want you to soak first, then cut. Others want the cut made immediately. Check your kit’s specific instructions and make sure you didn’t skip the soak entirely, most commercial sawdust blocks need an initial 5-10 minute submersion or thorough saturation before anything else.
What Is That White Fuzzy Stuff
Put down the hydrogen peroxide.
This is where most beginner kits get destroyed. White fuzzy growth on your substrate block is mycelium. That’s the fungus doing exactly what it’s supposed to do. Healthy mycelium is bright white, hugs the surface of the substrate, and spreads slowly, it takes 10-20 days to fully colonize a block. If you want to read more about keeping conditions right during this stage, my mushroom humidity guide covers the environmental basics in more detail.
Cobweb mold, the thing everyone is actually worried about, looks completely different. It’s light gray (not white), floats above the substrate surface in a wispy cloud, and it moves fast. Cobweb can overtake a tub in 24-48 hours. If your white growth has been sitting there for days and not exploding, it’s mycelium.
And, if you’ve already sprayed hydrogen peroxide on white growth that turned out to be mycelium, don’t do it again, targeted use only, never a full drench.
Here’s a quick reference:
| What you see | What it is | What to do |
|---|---|---|
| Bright white, hugs surface, slow spread | Mycelium | Nothing. Let it grow. |
| Light gray, floats above surface, fast spread | Cobweb mold | Spray with 3% H2O2, cover overnight |
| Blue-green or emerald patches with white ring | Trichoderma | Remove kit from your space immediately |
| Slimy dark patches, sour smell | Bacterial contamination | Discard. It’s not recoverable. |
| White layer covering entire block face | Thick mycelium overlay | Scrape with fork until brown substrate shows |
Trichoderma is the one that actually warrants panic. It’s a vivid emerald or yellowish-green mold with a bright white border, and it will spread to anything nearby. If you see it, seal the kit in a bag and get it outside. If you do end up replacing a block, my four-kit oyster comparison covers which ones hold up best.
For the white fuzzy stuff that’s thick and mat-like across the whole surface (called overlay), scraping it with a fork until you see brown substrate actually stimulates pinning. That’s a feature, not a bug.
If you do have cobweb mold, a diluted 3% hydrogen peroxide spray melts it on contact. But be careful, over-spraying healthy mycelium with H2O2 acidifies the substrate and can invite real problems. Use it targeted, not as a whole-block drench.
🌿 Best for Serious Growers
North Spore Organic Lion's Mane Mushroom Grow Kit, 4 lbs
4 lb lion's mane kit yields 0.5-1.5 lbs mushrooms in 14-21 days with daily misting, ideal for indoor countertop growing.
Check Price on AmazonThe Block Is Drying Out
This one is simple and annoying in equal measure. Dry substrate stops producing. The fix is misting, but the frequency depends on your environment in ways the kit instructions don’t account for.
A kitchen running at 40-50% relative humidity needs 3x daily misting minimum. A humid apartment in summer might be fine with once. The actual signal is the surface feel: consistently damp, never crusty.
If you’re losing moisture fast and can’t keep up, build a simple humidity tent. A clear plastic bag over the opening (not sealed, just draped) with a few holes cut in it traps moisture without killing airflow. This is what North Spore recommends if the block dries out and needs recovery: tent it with a bag, mist inside daily, watch for pins before removing.
One thing most growers don’t do: check whether the block itself has pulled away from the bag sides. If there’s a visible air gap between substrate and plastic, the edges are drying faster than the middle. You can press the bag gently back against the block to restore contact, or just increase misting frequency around the edges.
But, if the surface has already gone hard and crusty, a longer soak, not just misting, is what the block actually needs to recover.
Forest Origins Pink Oyster Mushroom Grow Kit, Beginner ...
Single pink oyster fruiting block yields harvest in 10 days with daily misting, ideal for indoor beginner growers.
Check Price on AmazonMushrooms Are Growing Inside the Bag
This one confuses people because the kit seems to be working, just… in the wrong place.
Side pinning happens when pins form on the inner walls of the bag before you’ve made your opening. It usually means the kit is ready and you waited slightly too long to cut, or light and CO2 gradients inside the bag pushed pins toward a gap or transparent section. Forest Origins Pink Oyster check current price kits tend to pin aggressively once they’re ready, and pink oyster in particular will pin wherever it finds the right conditions.
The fix: cut the bag open where the pins are, not where you originally planned. Pins forming on the side or bottom of the bag are still harvestable, just cut to accommodate them. Don’t try to redirect growth or wait for the kit to produce somewhere more convenient.
For the Forest Origins Specialty Trio see on Amazon , this applies to all three species in the kit. Different oyster varieties pin at different rates, so if one side of the block is pinning while another looks dormant, open where the activity is and let the other side develop on its own schedule. If you’re still deciding which kit to start with, my guide to the best mushroom grow kits breaks down how the main options compare for beginners.
No Second Flush, or a Weak One
Kit instructions typically say “wait 2-3 weeks” for a second flush. That’s accurate but incomplete.
The step most instructions skip is a cold soak before waiting. After harvesting the first flush, scrape the surface lightly with a fork, then submerge the block in cold water for 6-12 hours (overnight works well). This temperature shock mimics the conditions that trigger fruiting in nature. Mushrooms fruit because something changed, in the wild, that’s usually a drop in temperature or a rain event. The cold soak recreates that signal.
After soaking, cut a new opening on the opposite side of the block if your kit allows it. Resume misting. Second flushes typically produce fewer mushrooms than the first, and that’s normal. If you’re not seeing anything after 3 weeks with the cold soak protocol, the block may be exhausted.
The Lion’s Mane Grow Kit check price on Amazon can sometimes produce 2-3 flushes with this method, though lion’s mane second flushes are noticeably smaller. Worth trying before discarding a block that produced well on the first round.
When to actually give up: visible trichoderma, persistent sour smell, or a block that’s completely dried and crumbled. Soft and moist with no activity after a cold soak is worth waiting on. Hard, dry, and green is done.
This article is part of my Growing Gourmet Mushrooms at Home: Complete Guide , a complete resource for growing gourmet mushrooms on your counter.
Frequently Asked Questions
Why is my mushroom kit not growing after 2 weeks?
The surface needs to stay consistently moist, press a fingertip against the cut and it should come away damp. If it’s dry, mist more aggressively and more often. Temperature is the second check: below 65°F, growth slows substantially, and air conditioning in dry climates can push the ambient temp low without you noticing. Give the kit 14 days before concluding it won’t produce, but only if moisture and temperature are actually in range.
How do I tell the difference between mycelium and mold?
Speed is the clearest signal. Cobweb mold can cover an entire tub in a day or two. Mycelium takes 10-20 days to spread across a block. If the white growth has been sitting there for several days without dramatically expanding, it’s mycelium. Cobweb is also gray and floats above the surface, healthy mycelium is bright white and stays pressed against the substrate.
Why are my mushrooms growing on the sides of the bag?
Side pinning means the kit is ready and found a favorable spot before you opened it. Cut the bag where the pins are forming, not somewhere more convenient. Trying to redirect active pins usually damages them. It’s worth checking your kit more frequently after the first signs of colonization so you can open it before pins develop in inconvenient spots.
How do I get a second flush from my mushroom grow kit?
Harvest the first flush cleanly, scrape the surface with a fork, then soak the block in cold water for 6-12 hours. This cold shock is the step most kit instructions don’t mention, and it makes a real difference in triggering a second round of pinning. After soaking, cut a new opening on the unused side if possible and resume misting. Expect the second flush to take 2-3 weeks and produce fewer mushrooms than the first.
What are the most common contamination types?
Trichoderma (blue-green or emerald patches) is the one that warrants immediate action, remove the kit from your space and dispose of it. Bacterial contamination shows up as slimy, wet, dark patches with a sour or rotten smell, and it’s not recoverable either. Cobweb mold is gray and fast-moving but treatable with 3% hydrogen peroxide if caught early. Almost everything else that looks alarming is probably just mycelium.