In this article, we’ll break down when mycelium is fully colonized, how to spot the first signs of fruiting, and when to move your mushroom blocks from the incubator to the grow room.
Table of Contents:
As mycelium colonizes the substrate, the color changes from pale to bright, dense white. The block becomes firm to the touch, as the hyphae weave tightly together. This is your sign that colonization is complete.
💡Always wait until the block becomes fully white and solid — that’s when the mycelium is ready.
With time and experience, you’ll learn to distinguish a healthy colonized block from one that’s just covered with stroma (a sterile white mass).
📌 Read more about that here.
If the bag is fully white, feels dense, and white fluffy mycelium is now visible in the slots, you can move the block to the grow room even before pins appear.
Look closely at the slots: when tiny bumps — 📌 hyphal knots — start forming there, it means the mycelium is preparing to fruit.
In these photos, you can see healthy, fully colonized blocks.
As soon as primordia (pins-baby mushrooms) appear — even just 1–2 pins on 5–10% of the bags — it's time to move the whole batch into the grow room. These first pins are called signal primordia.
⚠️ Don’t wait for mass pinning! In the incubator, high CO₂ levels can suffocate pins within a couple of days, causing them to yellow, wilt, or die. Remove these dead pins to avoid contamination. In 4–5 days, healthy clusters will usually begin to grow from the same openings.
How fast mushrooms fruit depends on several things — including your grow room conditions and the strain you’re growing.
Warm-weather strains may take a bit longer to develop fruiting bodies at 20 degrees Celsius (68 degrees Fahrenheit) compared to cold-tolerant strains, which are in their optimal temperature range at 14–15 degrees Celsius (57–59 degrees Fahrenheit).
💡 In general, at 14–17 degrees Celsius (57–63 degrees Fahrenheit), fruiting takes about 5–6 days, while at 20–22 degrees Celsius (68–72 degrees Fahrenheit), it can happen in just 1–2 days.
On average, oyster mushrooms fruit 21–24 days after inoculation. But if it’s been over a month with no pins, you may need to reassess your conditions.
It depends on several factors:
Some strains colonize in just 9–10 days. Pins may appear by day 10–11, and fruiting finishes in 2–3 days.
Such is the summer strain of pulmonary oyster mushroom pph (Pleurotus pulmonarius).
📌 You can read about it and other strains in this article.
Other strains need 16–20 days to fully colonize.
💡 Always check the strain datasheet for the ideal timeline and growing conditions.
With the right ratio of essential nutrients and trace elements, mycelium colonizes the substrate quickly and produces primordia (pins) two or three days earlier than it would on a poorly balanced substrate.
▶️ Even when all other conditions are the same, a substrate made from sunflower husks usually pins a couple of days earlier than one made from straw or a straw-hay mix.
▶️ Cotton waste substrates may colonize more slowly than husk or straw, but when properly treated and well overgrown, they often reward you with excellent first-flush yields — up to 26–28%.
Also, if the raw material is properly treated (pasteurized, sterilized, etc.), the mycelium grows without wasting energy on fighting contaminants.
Use certified grain spawn or carefully cultured spawn. Otherwise, colonization may look fine but result in no mushrooms.
The typical spawn rate is 3–5% of the substrate weight.
▶️ Higher rates = more growth points = faster pinning.
💡 But: this doesn’t increase total yield — just shortens the timeline.
At our facility, we pasteurized 10–11 tons of substrate (barley and wheat straw + 4–5% alfalfa hay).
We used oat grain spawn at a 3% rate (360 grams per 12-kilogram block, or about 12.7 oz per 26.5 lb block).
Using less (e.g. 2.7%) slowed colonization by 1–2 days.
It’s not enough to simply wait the right number of days — you also need to monitor temperature, humidity, and carbon dioxide levels (at the end of incubation) in the incubator.
📌 Read more about incubation conditions here.
▶️ If the temperature drops below 14 degrees Celsius (57 degrees Fahrenheit), colonization slows dramatically — sometimes pins form only after 35–40 days.
▶️ Low humidity (<80%) dries out the slots and delays pinning.
Take a look at the photo: the substrate near the slot is dry, with no visible mycelium. Pins have started forming deeper under the plastic, where there’s still enough moisture.
To grow beautiful, heavy mushrooms, all climate conditions must be optimal at the same time.
Even if the temperature and humidity are perfect, a high level of CO₂ will still cause visible problems. And if CO₂ and humidity are fine but the temperature is too low, the shape of the mushrooms will also be affected.
Now imagine that one of the climate parameters shifts out of the ideal range — it could be temperature, humidity, or airflow.
So what can you do?
You have two options:
✅ First — bring that one parameter back to normal and keep all the others within their recommended range.
✅ Second — adjust the rest of the parameters to match the one that’s off.
This second option is often what we have to do — especially in winter.
💡 For example: if your boiler can’t keep the grow room at the optimal temperature during cold weather, don’t try to “compensate” by heating during the day and letting it cool at night. It’s much better to stabilize the room at a slightly lower temperature — even if it’s not ideal.
Mushrooms will grow more slowly, but they’ll need less fresh air, and the boiler will be able to maintain a constant temperature.
Also, remember to lower the humidity. When the temperature drops, the air (and mushrooms) can hold less moisture.
When all parameters are balanced relative to each other, mushrooms will grow with the right shape — even if conditions aren’t technically “perfect”.
📌 Read here about the optimal humidity level for the incubation room and how to control it.
Yes — slightly.
As the mycelium grows, it consumes the nutrients and releases CO₂ and water vapor.
▶️ That leads to a small weight loss: about 2–3% under normal humidity.
▶️ With low humidity, it can be as much as 10–15%.
At first, the bag smells like steamed plant material.
After 4–5 days of growth, a mild, sweet, milky smell appears.
Experienced growers can walk through the incubator and detect problem blocks by smell.
For example, if a block lacks perforations or has bacterial contamination, the smell turns sharp and straw-like.
We used to remove any bag with a foul odor and dump it in the compost pit.
By days 7–8, especially with husk-based blocks, the CO₂ levels were so high that it felt like “breathing under a blanket.” But in smaller incubators with staggered-age blocks, this isn’t usually noticeable.
Emoji guide: 📌 link | ✅ advice | ▶️ fact | 💡 important | ⚠️ warning
