What is colonization?

Colonization is complete when no bare grain or substrate shows, but what "done" looks like depends on the species.

• Grain. A jar is fully colonized "when the grain is completely covered with mycelium and uniformly white" (GroCycle).
• Bulk blocks. GroCycle calls a king oyster block colonized "when dense white mycelium has covered the substrate" (GroCycle).
• Faint species. Lion's mane mycelium "is very fine," which makes it hard to tell when it's done (GroCycle). North Spore notes it looks different from "the dense white mats of mycelium characteristic of oysters", and that spawn broken up in shipping can look uncolonized (North Spore help center). Judge these by bare kernels, not brightness; our pink oyster grain spawn guide does the same.
• Shiitake. Shiitake blocks stay in incubation until 75% of the block "has turned brown and popcorned" (Cornell).

Colonization takes about 2–3 weeks for grain (GroCycle) and 10–20 days for oyster on sawdust. Shiitake on sawdust spends 42–84 days in incubation; after full colonization, another 4–5 weeks of that go to popcorning and browning (Cornell). GroCycle gives lion's mane two to three weeks (GroCycle). The incubation page lists more, with the conditions to hold.

More spawn, spawn mixed all the way through and steady warmth make colonization faster.

• Spawn rate. In a Penn State trial on an oyster species, spawning at 3.75% of wet substrate weight instead of 1.25% cut the time to production by a mean of 9.2 days (Penn State, via PubMed).
• Mixing. When a Fungi Ally crew skipped shaking half its bags, the through-spawned bags were fully colonized in 14 days. The top-spawned bags took 24 (Cornell).
• Shaking grain. Some growers shake jars about a third of the way colonized (GroCycle), the break and shake.
• Temperature. Cool rooms slow it: Cornell says incubation can run as low as 50°F (10°C) but takes longer (Cornell). GroCycle colonizes lion's mane in a dark, warm spot at 68–75°F (20–24°C) (GroCycle).

• Fruiting too early. Fresh air helps trigger fruiting, so keep blocks sealed until they're fully colonized (CO2 guide).
• Calling faint mycelium a stall. Lion's mane can look unfinished when it's ready.
• Missing contamination. Patches that outrun the mycelium, or green breaking through white, aren't colonization. See trichoderma and the contamination ID guide.

In Hypha, photograph a bag every few days and compare the photos side by side to see whether the bare patches are shrinking.