It might seem like a topic just for beginners — but even experienced growers can find something new here.
Table of Contents:
Primordia are the very first visible stage of mushroom fruiting bodies.
Once the mycelium fully colonizes the substrate, it begins to condense near the cuts in the bag, forming a dense white mass that soon transforms into tiny mushroom formations — the primordia.
First, you'll notice a white ridge of hyphal tissue near the slots — a clear sign that pins will form in the next day or two.
Hyphal knots are compact formations of mycelium hyphae that later develop into primordia. They’re the first visible sign that the fruiting process is beginning.
They usually look like dense white tissue around the film cuts.
📸 On round holes, they’re easy to spot as distinct rings (photo on the left).. On other shapes, they may look like puffy white buildup around the edges.
✅ If you're using a single-zone system, you can start gradually adjusting the climate when hyphal knots appear.
✅ In a two-zone system, move the blocks when you see one or two pins on a few bags — these are called signal primordia.
At optimal temperatures, it takes 2 to 3 days for hyphal knots to turn into pins.
⚠️ If the grow room is cooler (below 17 °C / 63 °F), the process slows down — pins might take 5–6 days to appear.
In heat-loving strains like golden or pink oyster mushrooms, low temperatures may completely stall pin formation, even if hyphal knots are visible.
📌 Read about the optimal temperature in the incubator.
Different countries use different terms for each stage of fruiting body development, so let’s clarify the sequence:
▶️Early primordia look like tiny foam bubbles — some describe it as “semolina.”
Soon after, you’ll see small, white spheres — this is the pin stage.
A day later, pins develop a gray or gray-brown tint, depending on the strain.
📸 Below are four photos showing the same slot at different stages — from hyphal knots to a full fruiting cluster.
Mushroom pins are the early, visible beginnings of mushrooms.
🌍 Terms vary by region:
💡 In this article:
In many places, all early forms are simply called primordia. Once they grow bigger, the clump becomes a “cluster” or “druze.”
From the first white primordia to visible pins takes 24 to 36 hours, depending on conditions.
In single-zone systems (where you gradually reduce temperature), pins form faster.
Maintaining proper humidity is especially important during this phase.
📌 Read about the humidity in the incubator.
📸 Check out the four-stage photo comparison to see the progression.
hyphal knots
Primordium stage
📸 In the left photo, you can see the moment mushrooms start dividing — this is the right time to transfer the blocks.
⚠️ Wait too long (like in the next photo), and some pins may die from condensate buildup.
Whether condensate forms on the primordia depends on room conditions.
For example:
• fruiting room: 12–13 °C (54–55 °F), 87-89% humidity
• Incubator: 20–21 °C (68–70 °F), 79-80% humidity
• Humidity difference: 8–9%
💡 In this situation, cold air plus higher humidity = water droplets on the caps = suffocation.
📌 Color depends on the strain.
⚠️ Color should be even.
Any plaque, scales, or deformities mean something’s wrong — either poor incubation conditions or sudden climate changes when moving blocks.
Timing depends on two things:
1. Incubation Conditions
2. Mycelium Growth Factors
📌For details, read this article: When is mycelium ready to fruit?
Emoji guide: 📌 link | ✅ advice | ▶️ fact | 💡 important | ⚠️ warning
