How to Grow Shimeji Mushroom (Hypsizygus tessellatus)

• 1 lb dry rye berries (or wheat berries, millet, or oats)
• Filtered water for soaking
• Medium grow bag with 0.2-micron filter patch
• Pressure cooker

Scale-up: 3 lbs grain → 3 grow bags; 5 lbs grain → 5 grow bags.

Rinse the grain, then soak it submerged in water for 12–24 hours at room temperature. After soaking, drain the grain and simmer in a pot of water for 10–15 minutes until the kernels are cooked through but not splitting. Drain thoroughly and spread on a clean towel to surface-dry for 30–60 minutes — kernels should feel dry to the touch with no visible moisture on the surface, though still moist inside. Load into polypropylene grow bags, leaving 30–40% headspace, and seal the bags by folding and clamping or heat-sealing above the filter patch. Sterilize at 15 PSI for 90–120 minutes. Allow bags to cool completely to room temperature before inoculating — warm grain kills liquid culture.

Out-Grow also carries sterilized grain spawn bags ready to inoculate if you want to skip this step.

• Out-Grow Golden Brown Beech Hypsizygus tessellatus liquid culture syringe (or White Beech)
• 3–5 cc liquid culture per 1 lb grain bag
• 70% isopropyl alcohol for wiping injection port or needle
• Still-air box or flow hood

In a still-air box or under a flow hood, wipe the injection port or filter patch injection site with 70% isopropyl alcohol and allow it to dry for 30 seconds. Inject 3–5 cc of shimeji mushroom liquid culture per 1 lb grain bag through the self-healing injection port or directly through the filter patch with a sterile needle. Withdraw the needle quickly and wipe again with alcohol. Shake each bag to distribute the liquid culture evenly through the grain.

• Inoculated grain bags from Step 2
• Colonization space at 70–75°F

Place inoculated bags in a dark or low-light space at 70–75°F. Keep bags undisturbed for the first 5–7 days to allow mycelium to establish. After the first week, shake bags once to break up colonized grain and redistribute moisture and mycelium through uncolonized kernels. Shimeji mushroom (Hypsizygus tessellatus) is a slower colonizer than oysters — expect 25–45 days for full grain colonization. Healthy mycelium appears dense, bright white, and consolidated across all the grain. Discard any bag showing green, black, or yellow patches, or a sour odor.

• 4 lbs hardwood fuel pellets (oak or maple), expanded into sawdust with hot water
• ¾ lb wheat bran
• ¼ lb agricultural gypsum
• ~5½ cups water (added gradually)
• Large grow bags with 0.2-micron filter patch
• Pressure cooker

Scale-up: multiply all dry ingredients by 3 for 3 blocks; by 5 for 5 blocks. Water adjusts to field capacity — squeeze test applies at each scale.

Expand the hardwood fuel pellets by pouring hot water over them and stirring until fully broken down into fluffy sawdust. Allow to cool slightly, then combine with wheat bran and gypsum. Add water gradually, mixing thoroughly, until the substrate reaches field capacity — when you squeeze a handful firmly, only a few drops of water should fall. Load substrate into large grow bags, packing to about 5 lbs finished weight per bag. Fold and seal the tops above the filter patch. Sterilize at 15 PSI for 90–120 minutes.

Out-Grow carries wood-based mushroom substrate bags ready to inoculate if you want to skip this step.

• Fully colonized grain spawn bags from Step 3
• Cooled sterilized substrate bags from Step 4
• Still-air box or flow hood
• 70% isopropyl alcohol

Spawn rate: approximately 1 lb colonized grain spawn per 5 lb substrate block. For 3 blocks, use 3 lbs grain; for 5 blocks, use 5 lbs grain.

In a still-air box or under a flow hood, wipe down all external surfaces with 70% isopropyl alcohol. Break up the colonized grain fully inside the closed spawn bag before opening — squeeze and knead the bag until every kernel separates and flows freely. Open the substrate bag and the spawn bag in the still-air environment. Pour the broken grain spawn evenly across the top surface of the substrate, then fold the substrate bag closed and knead and mix from the outside until no isolated clumps of grain remain anywhere in the block. Seal the bag above the filter patch.

• Inoculated substrate bags from Step 5
• Space at 70–75°F, dark or low light

Place inoculated blocks in a 70–75°F space in darkness or very low light. Keep bags sealed — the filter patch handles gas exchange. Do not disturb bags during colonization. Hypsizygus tessellatus colonizes hardwood blocks slowly; expect 30–45 days for a fully colonized block. The block surface should become consolidated, firm, and uniformly white with a slight skin forming across the entire face. Any temperature below 65°F will significantly slow colonization; above 80°F risks contamination and poor mycelial quality.

• Fully colonized block from Step 6
• Fruiting chamber or grow tent held at 50–60°F
• Humidity source to maintain 98–100% RH
• Fresh-air exchange: 4–8 air exchanges per hour, CO₂ target 500–1,000 ppm
• Diffuse light: 400–600 lux on a timer (12 hours on/12 hours off)

Cut open the top of the bag or fold it down to expose the block surface. Move colonized blocks into a fruiting environment held at 50–60°F. Increase relative humidity to 98–100% using a humidifier, ultrasonic mister, or frequent misting. Begin fresh-air exchange at 4–8 exchanges per hour — shimeji mushroom (Hypsizygus tessellatus) is highly sensitive to elevated CO₂ (the gas produced by mycelium respiration) during pinning; keeping CO₂ below 1,000 ppm is critical for compact, properly formed clusters. Provide 400–600 lux of diffuse light on a 12/12 schedule. Pins (primordia) should appear within 7–12 days as dense clusters of tiny white-to-pale-brown buttons.

• Fruiting chamber at 55–65°F
• Relative humidity: 90–95% during development
• FAE: 4–8 exchanges per hour maintained throughout
• Diffuse light: 400–600 lux, 12 hours on / 12 hours off

Once pins are established, maintain temperature at 55–65°F and ease humidity slightly to 90–95% RH — high enough to prevent cap cracking, low enough to discourage bacterial issues. Continue FAE at 4–8 exchanges per hour throughout development. Clusters develop relatively slowly compared to oysters; allow 5–10 days from pinning to full development. Avoid directing fan airflow directly at exposed block surfaces, as shimeji mushroom clusters are sensitive to surface drying during development.

• Clean, sharp knife or scissors
• Clean surface for harvested clusters

Harvest shimeji mushroom (Hypsizygus tessellatus) clusters when caps are still convex to very slightly flattened and cluster structure is dense and firm. Do not wait for caps to fully open or flatten — over-mature clusters drop spores, develop tougher texture, and begin to show yellowing or browning at the cap edges. Cut each cluster cleanly at the base of the stems where they meet the block surface, using a knife or scissors. Avoid twisting or pulling clusters, which can disturb the remaining block surface. Remove any remaining stem stubs from the block after harvesting.

• Harvested block from Step 9
• Clean water for rehydration (dunk or misting)

After harvesting, fold the bag back over the block or cover the exposed surface to retain moisture. Allow the block to rest for 5–7 days in the fruiting environment before attempting a second flush. If the block has lost significant weight and feels light, submerge it in clean cold water for 2–4 hours to rehydrate, then drain and return to fruiting conditions. Repeat the temperature, humidity, and FAE conditions from Step 7–8. Shimeji mushroom blocks typically produce 2–3 flushes before yields decline significantly. Discard blocks that show persistent green mold, slimy or yellowing spots, or that fail to pin after a second conditioning period.

• 2 lbs hardwood fuel pellets (expanded), per bottle batch
• ⅓ lb wheat bran
• 2 tbsp gypsum
• ~2½ cups water (to field capacity)
• Wide-mouth polypropylene bottles with filter lids

Expand hardwood fuel pellets with hot water and mix in wheat bran and gypsum. Add water gradually, mixing until the substrate reaches field capacity — squeeze a handful and only a few drops should fall. Fill each bottle to about ¾ capacity, packing lightly. Cap with modified filter lids. Sterilize at 15 PSI for 60–90 minutes. Allow bottles to cool completely.

Follow the same liquid culture inoculation procedure as Method 1, Step 2, injecting 3–5 cc of shimeji mushroom liquid culture per bottle through the filter lid or a self-healing port. Swirl each bottle after inoculation to distribute the culture. Colonization in bottles follows the same parameters as Method 1, Step 6: 70–75°F, 30–45 days to full colonization.

• Fully colonized bottles from Step 2
• Sterile tool (bent wire or spoon) for scratching
• Cool water for surface watering
• Fruiting environment at 50–60°F, 98–100% RH, CO₂ below 1,000 ppm, 400–600 lux light

In a still-air environment, use a sterile bent wire or spoon to scratch the top ¼ inch of the colonized substrate surface in each bottle — this removes the dense surface layer of mycelium and signals the fungus to shift from vegetative growth to fruiting. Add a small amount of cool, clean water to each bottle top (about 2 tbsp), allow it to sit for 1–2 minutes, then pour off the excess. Cap loosely or with the filter lid to maintain humidity. Move bottles to a fruiting environment at 50–60°F with 98–100% RH and fresh-air exchange sufficient to keep CO₂ below 1,000 ppm. Provide 400–600 lux of diffuse light on a 12/12 timer. Pins should appear within 7–12 days.

Harvest shimeji mushroom clusters from bottles by cutting cleanly at the substrate surface with scissors or a knife, following the same visual harvest cue as Method 1, Step 9 — convex caps, firm stems, dense cluster structure. After first flush, scratch the surface again, re-water, and repeat the fruiting trigger for additional flushes.