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The Spawn Run


Place the bag gently where it gets little or no light, some ventilation, and where you can check it easily. You will want to watch the fine, white fibers of mycelium spread through the substrate, in the phase we call the spawn run. You can keep it in a lighted space — like your living space — in a paper bag or box to shade it. Keep the box top open for air, though. Don’t smother it in a tight space like a drawer. A temperature around 65°F is ideal, but it will do fine between 50°F and 80°F.
After about a week, examine the bag daily—the next stage happens suddenly! Look for spots where the cottony fibers thicken into solid, flat masses on the surface of the substrate. In about 10 –14 days they should start pinning: forming tiny mushroom pinheads. Ideally you will want to cut an opening in the bag just as the block starts pinning, as described in the next section.