Why aren't my mushrooms pinning? How to diagnose no pins, stalled pins and side pins
Mushrooms that won't pin are usually too dry, short of fresh air, at the wrong temperature or not ready yet, and this guide shows how to tell which. It covers stalled pins, side pins, mushrooms inside the bag and the North Spore kit reset.
Derick9 min read
Mushrooms that won't pin usually mean the block is too dry, short of fresh air, at the wrong temperature or not finished colonizing. Work through the symptom table below, change one thing at a time, and give each change time to show before the next.
Our sources are UF/IFAS Extension, Cornell (via our timeline guide), the American Mushroom Institute, peer-reviewed research, GroCycle and North Spore, all checked 21 October 2026. We label our own advice and link our other guides for the numbers.
Why aren't my mushrooms pinning? Start with the symptom
The fastest way to find why a block won't pin is to match what you see to its likely cause.
| What you see | Likely cause | Check first | Read more |
|---|---|---|---|
| White and firm, no pins | Not fully colonized, or not long enough in fruiting | Date it went into fruiting | Ready? |
| Colonized, surface dry or cracked | Too dry | Humidity around the block | Too dry? |
| Thick, leathery mat on a block | Overlay: mycelium kept growing instead of pinning | Fresh air | Fresh air |
| Pins form, then stall or shrivel | Humidity dips, drafts or heat | Overnight humidity | Stalled pins |
| Side pins, or mushrooms inside the bag | Air between plastic and block, or long storage | Where the plastic lifted | Side pins |
| Kit did nothing after two weeks | Dry, broken in transit, or faint lion's mane mycelium | Moisture | Kit check |
| Cold room, or a heater cycling nearby | Too cold, or fast swings | Temperature day and night | Temperature |
| Kept in a closet or cabinet | Too little light | Where it sits | Light |
| Fruited once, now nothing | Needs rest and water | Misting since harvest | Second flush |
| Sour smell, slimy grey patches, or green, black or orange spots | Contamination | Smell and color | Contamination guide |
Is the block ready to fruit?
A block usually pins once it's fully colonized (for shiitake, about 75% brown, not white) and has had time in fruiting conditions, so check both before you change anything. Bare patches mean the block hasn't finished colonizing, and our colonization guide shows how to tell slow from stalled, and our stages guide shows what a fully colonized bag looks like. Our timeline guide shows when each stage is finished, including for lion's mane. Don't rush shiitake: Cornell warns that a cold drop or a move can set off early fruiting that greatly reduces yields (timeline guide).
Is the block too dry to pin?
Dryness is a common cause when a colonized block won't pin. North Spore's help center says: "If your kit is fully myceliated, but won't form pins, it might be dry. Try using a humidity tent" (North Spore help center).
Heating season makes this more likely. Electric heaters lower relative humidity and fan heaters dry blocks, as our grow room guide explains.
For a humidity tent, drape "a semi-transparent trash bag" with "plenty of 1/2 inch holes" over the kit. Mist inside several times a day; once pins form, you can remove it and keep misting the kit (North Spore help center).
Mist from a distance with a fine spray: GroCycle warns that "direct, close proximity misting" damages "the fragile primordia" (GroCycle). Our humidifier guide lists signs of too little and too much humidity, and the Martha tent guide gives humidity targets.
Is it getting enough fresh air?
A sealed bag or tub holds in CO2, and blocks often sit white instead of pinning until they get fresh air. Our CO2 guide gives safe levels by stage and signs of too much.
For a cut-and-grow bag kit, the cut is the air supply. North Spore says the X cut on its Spray and Grow kits lets oxygen reach the block and "directs the mushrooms to form there" (North Spore help center). A thick, leathery mat may be overlay, mycelium that keeps growing instead of pinning. On button-mushroom casing, the American Mushroom Institute links overlay to temperature and CO2 left "too high" for "too long" (AMI). The contamination guide lists it among look-alikes.
Is the temperature holding pins back?
Temperature can hold pins back: a room that's too cold slows pinning, and one that swings fast can stall or abort it. A drop helps some species pin but isn't a universal switch. A 2020 button-mushroom review says "for most basidiomycete species [most mushrooms], nutrient availability, light and a drop in temperature are critical factors for fructification [fruiting]" (Molecules, via PMC).
Our temperature guide covers when the drop helps and the ranges by species.
Rooms cool off in fall, and Cornell says cooler fruiting rooms slow mushrooms down (timeline guide). A space heater cycling on and off also causes fast swings.
Do mushrooms need light to pin?
Most gourmet mushrooms use some light as a fruiting cue, but the research disagrees on whether oysters need it to pin at all. Give blocks modest light, but don't expect light alone to fix a stall. Researchers call pins primordia.
- UF/IFAS Extension: "Initiation of the fruiting phase of many oyster mushrooms requires a lower temperature of 20°C (68°F) and light" (UF/IFAS).
- A review of oyster research says "Photoperiod [a light schedule] is not necessary to induce the primordium formation but it is needed for fruiting body production". It also says "Pleurotus spp. or L. edodes require light for primordia formation" (PMC).
- A trial at Penn State's Mushroom Research Center (published 2026) found "Light treatments did not affect total primordia production" (Frontiers).
North Spore's help center says pale caps "likely need more natural light" and to avoid "keeping your kit in closets or cabinets" (North Spore help center). For how much light, and what darkness does to caps, see our grow room guide.
Why are my mushroom pins not growing?
Stalled pins are usually a humidity problem, though heat and drafts can stop them too. North Spore's help center says: "Usually, mushroom pins abort when there isn't enough humidity around the block" (North Spore help center).
Not every pin grows: "The fungus selects the healthiest, most viable pins" (GroCycle). By our reading, a few stalled pins in a growing cluster are normal; a whole cluster drying off is not.
Our Martha tent symptom table covers the usual culprits, such as a humidifier running dry overnight.
If pins started and then dried, North Spore's reset is:
- Pick off the dried-up pins.
- Wait one week, "letting the block dry out on a plate".
- Soak the block for 20 minutes in cold water, or 5–10 for lion's mane, which can "break apart if soaked for too long" (North Spore help center).
- Drain all the water out of the kit (for species that grow in the bag).
- Start again. If you didn't use a humidity tent the first time, North Spore says one "may be helpful the second go around" (North Spore help center).
Soak times vary even between North Spore's own pages: its dry-kit page says an hour for oysters (North Spore help center).
Why are mushrooms pinning on the sides or inside the bag?
Mushrooms tend to pin where the block meets air, so side pins usually mean air got between plastic and block, and mushrooms inside the bag can mean long storage. North Spore's kit FAQ says mycelium grows toward the bag's filter, and that stored kits "may start fruiting inside the bag" (North Spore — affiliate link: we may earn a commission at no extra cost to you).
To keep pins at the opening, North Spore says to "squeeze out any air left in the bag after you slice it" and fold the flap under, so the mushrooms grow from the opening and not inside the bag. That applies to its advanced kits other than shiitake. Its shiitake kits come fully out of the bag instead, and exposing the whole block means "mushrooms will form all over" (North Spore help center).
Mushrooms already inside? For oysters, lion's mane, pioppino and chestnut, North Spore says "you can ignore" them or compost any you can reach. For shiitake, "pinch off and compost any of the premature pins" (North Spore help center).
Our own fix, not a sourced one: press or tape loose plastic back against the block. If side pins are already big, cut the bag there and keep misting both openings. North Spore warns a second cut can let the block dry out (North Spore help center).
My grow kit did nothing after two weeks. What now?
A kit that's done nothing after two weeks may be dry, broken up in shipping, or a lion's mane kit whose faint mycelium only looks dead. North Spore calls lion's mane mycelium "notoriously fine". For a block broken in transit, it says to "gently press the kit together" and give it a few days. North Spore guarantees its kits "will fruit within two weeks, or we'll send you a replacement" (North Spore help center); for other kits, contact the seller. If it's dry, add a humidity tent.
Spots are a different problem: see whether your kit is contaminated.
What if it fruited once and won't pin again?
A block that has fruited once needs time and steady misting before it pins again, and each later flush can take a little longer (North Spore help center). North Spore says: "If you don't see any baby mushrooms (pins) forming after a week or two, it's a good idea to soak your block" (North Spore help center). Our timeline guide lists the gap between flushes, and our second-flush guide covers rest and soaking.
What to write down while you wait for pins
A stall is only diagnosable if you know what changed, so write down each change the day you make it. For pinning, note these (full field list):
- the date the block went into fruiting
- how and where you cut the bag
- your misting and fan routine
- room changes: heater on, block moved, window opened
- the date pins first showed
In Hypha, each block's timeline shows when it moved into fruiting and how long each stage has run. Write changes in the block's notes, or append one note to many blocks at once. Photograph the block daily in its photo journal and compare two days side by side.
Hypha has no pin-date field or typed-in hygrometer readings, so put both in the notes. Download Hypha; the free plan holds 25 active blocks, and each block counts until you archive it.
FAQ
How long should I wait for mushrooms to pin?
How long mushrooms take to pin depends on species and conditions; North Spore guarantees its kits will fruit within two weeks (North Spore help center). For blocks, see the timeline guide's stage table.
What triggers mushrooms to pin?
Mushrooms pin when a colonized block gets the right cues. A 2020 review, mainly of button mushrooms, names nutrient availability, light and a temperature drop as critical for most mushroom species (Molecules, via PMC). Fresh air and humidity matter too. Cold shocking isn't a universal switch: our temperature guide explains where the drop helps.
My block is fully colonized but not pinning. Will it fruit?
A fully colonized block that isn't pinning is often just dry, and North Spore suggests a humidity tent (North Spore help center). If it smells sour or shows green, black or orange patches, check the contamination ID table.