Step 4: Watch Your Mushrooms Grow — What to Expect During Development

Once you have cut the bag, started misting, and placed your kit in a suitable location, the next stage is observation. Mushroom development happens faster than most people expect — some species go from the first visible pin to a harvestable cluster in under a week. Understanding what healthy growth looks like at each stage helps you know when everything is on track and when you might need to adjust your humidity, airflow, or temperature.

Days 1-3: Primordia Formation

In the first few days after cutting the bag, you may not see any visible change at the opening. Behind the scenes, the mycelium is sensing the shift in gas exchange, humidity, and light. It is beginning to form dense clusters of hyphal knots just beneath the surface — the earliest precursors to mushrooms. These structures are called primordia, and they represent the mycelium’s commitment to producing fruit bodies rather than continuing vegetative growth.

Some species form primordia faster than others. Oyster mushrooms are among the fastest — you may see tiny bumps or pin-like structures emerging from the cut edges within 3-5 days. Lion’s mane typically takes 5-10 days before visible primordia appear. If you do not see any development after 14 days, check your humidity levels and make sure the substrate has not dried out around the opening.

Days 3-7: Pinning

Primordia that receive consistent humidity and fresh air will develop into pins — tiny, recognizable baby mushrooms that emerge from the substrate surface. Oyster mushroom pins appear as small, rounded nubs that quickly develop into miniature versions of the mature mushroom. Lion’s mane pins look like small white fuzzy balls. Shiitake pins are tiny brown bumps with a distinct cap shape.

During the pinning stage, maintain your misting schedule carefully. Pins are the most sensitive stage of mushroom development — a single period of low humidity can cause an entire flush of pins to abort (dry up and stop growing). If you see pins that have darkened, shriveled, or stopped growing, it is almost always a humidity issue. Increase misting frequency and consider adding a humidity tent if you are not already using one.

Days 7-14: Rapid Growth

Once pins are established, mushroom growth accelerates dramatically. Most gourmet species double in size every 24-48 hours during this phase. An oyster mushroom cluster that was the size of a marble on Monday can be the size of a fist by Thursday and ready to harvest by Saturday. Lion’s mane fruit bodies expand from golf-ball size to softball size within days, developing their characteristic cascading spines as they mature.

During rapid growth, mushrooms are consuming large amounts of water from the substrate. Continue misting regularly and watch for any signs of drying at the cap edges. If mushroom caps appear cracked or leathery rather than smooth and moist, increase your misting frequency. This is also the stage where adequate fresh air exchange becomes most important — the growing mushrooms are producing significant CO2, and insufficient ventilation will cause elongated stems and undersized caps.

Troubleshooting Common Issues

Pins forming but aborting: Usually caused by a sudden drop in humidity. Increase misting or improve humidity retention with a tent. Long thin stems with small caps: Not enough fresh air. Fan more frequently after misting. Yellow or brown discoloration: Could be bacterial contamination from standing water — reduce direct misting on the substrate surface and improve air circulation. No pins after 14+ days: Check that the substrate at the opening is still moist. If it has dried out, mist heavily and consider making additional cuts. When your mushrooms look full-sized and healthy, it is time for the next step — Step 5: Using the Humidity Tent.