How to Grow Oyster Mushrooms

What You Need

• 200–250 g dry rye berries per quart mason jar
• 2% gypsum by dry weight of grain (4–5 g per 200 g rye)
• Water to cover grain by 1 inch
• Large pot, colander, and clean baking pan

What To Do

Place the rye berries in a bucket, add water to cover by 1 inch, stir in the gypsum, and soak for 24 hours at room temperature.

After soaking, drain and transfer the grain to a pot with fresh water covering the grain by 1 inch.

Bring to a gentle boil on medium-high heat, reduce to a simmer, and cook for 10 minutes — the grains should swell and hydrate but still hold their shape, not turn mushy.

Drain in a colander, shaking well to remove surface water. Spread the drained grain on a clean baking pan and air dry at room temperature for approximately 1 hour.

The exterior surface should lose its visible shine while the interior stays moist — grains that roll freely and separate when shaken are ready, while grains that clump together are still too wet and risk anaerobic bacterial growth during sterilization.

→ Ready for Step 2 when grains roll freely without clumping and the exterior surface is no longer glistening but the interior is still moist.

What You Need

• Prepared rye berries from Step 1
• Quart mason jars with polyfill filter lids
• Aluminum foil
• Pressure cooker (15 PSI rated)

What To Do

Fill quart mason jars ½ to ¾ full with the dried grain — do not pack. Install the polyfill filter lids and cover each lid with aluminum foil to protect the filter during sterilization.

Place a trivet in the bottom of the pressure cooker, add water to just below the trivet, and load the jars.

Heat on high with the lid on until steam escapes steadily for 10 minutes, then add the rocker weight to bring the cooker to 15 PSI (121°C / 250°F). Sterilize for 2–2.5 hours at 15 PSI.

This temperature is required to kill bacterial endospores including Bacillus species — lower pressure will not reliably eliminate them. After the cycle, allow the cooker to depressurize naturally. Do not force-cool.

Leave jars inside until they reach room temperature, which takes a minimum of 8 hours — overnight is ideal. Inoculating grain above 30°C (86°F) will kill the liquid culture mycelium.

→ Ready for Step 3 when jars are at room temperature and the grain inside is no longer warm to the touch through the glass.

What You Need

• Cooled, sterilized grain jars from Step 2
• Liquid culture syringe (10 mL, P. ostreatus)
• Still Air Box (SAB)
• 70% isopropyl alcohol spray bottle
• Nitrile gloves

What To Do

Wipe the interior of the Still Air Box with a damp cloth, then spray thoroughly with 70% isopropyl alcohol and allow to air dry for 5 minutes.

Spray all items entering the box — jars, syringe — with 70% IPA and wipe down. Put on nitrile gloves and spray them with IPA immediately before inserting your hands through the arm holes.

All hand movements inside the box must be slow and deliberate to avoid creating air turbulence that carries contaminants.

Flame-heat the needle of the liquid culture syringe until it glows red, then allow it to cool for 5–10 seconds.

Inject 1–2 mL of liquid culture into each quart jar through the polyfill filter or injection port, then immediately reseal the injection site. One 10 mL syringe will inoculate 5–10 jars.

→ Ready for Step 4 when all jars are inoculated and sealed with no visible damage to the filter lids.

What You Need

• Inoculated grain jars from Step 3
• Dark room at 22–26°C (72–79°F)

What To Do

Place inoculated jars in a dark location at 22–26°C (72–79°F).

Avoid temperatures above 28°C (82°F), which favor competing bacteria. First visible mycelium growth appears within 3–7 days from liquid culture, and full colonization takes 10–14 days.

Spore syringes take longer — 14–21 days for full colonization.

Watch for bright white, dense, ropy mycelium radiating outward from the inoculation points and eventually covering all grain surfaces.

Any green, blue, black, yellow, or orange coloration means mold contamination, and any slimy gray or dark patches with a sweet-sour or foul odor mean bacterial contamination — contaminated jars must be sealed and discarded immediately without opening them indoors.

Once mycelium has visibly established, you can shake the jar once mid-colonization to redistribute mycelium and speed the final phase.

Grain spawn is ready when 100% of the grain surfaces are covered with solid white mycelium. If you are not ready to use the spawn immediately, refrigerate at 2–4°C (35–39°F) for up to 2–4 weeks.

→ Ready for Step 5 when all grain surfaces in the jar are covered with white mycelium and the jar interior appears solid white.

What You Need

• 5 kg (11 lb) dry wheat or oat straw
• String trimmer, lawn mower, or straw chopper
• Pillow cases or nylon mesh laundry bags
• Clean bucket or garbage can

What To Do

Chop straw to 3–5 inch (7.5–12.5 cm) pieces.

The easiest method is to place straw loosely in a clean garbage can, insert a string trimmer, and run it until the straw is uniformly chopped.

Alternatively, run the straw over with a lawn mower.

Smaller particle size eliminates large air gaps between straw pieces — gaps of 1–2 inches force mycelium to bridge long distances, slowing colonization and reducing final yield.

Stuff the chopped straw into pillow cases or nylon mesh laundry bags and secure them with zip ties or string.

Pre-soak the bagged straw in clean water for 12 hours to fully hydrate it before heat treatment.

→ Ready for Step 6 when all straw is uniformly chopped to 3–5 inches, bagged, and has soaked for a full 12 hours.

What You Need

• Pre-soaked straw bags from Step 5
• Large stock pot, turkey fryer, or insulated cooler
• Probe thermometer
• Bricks or weights to keep bags submerged

What To Do

Heat a large volume of water in your stock pot, turkey fryer, or insulated cooler to 160–165°F (71–74°C). Submerge the straw-filled bags completely and use bricks or weights to keep them under the waterline.

Monitor the water temperature continuously with a probe thermometer for the full 60-minute treatment. If the temperature drops below 160°F, increase heat and extend the time to compensate.

A peer-reviewed study by Grimm, Sonntag, and Rahmann (2024) found that hot water pasteurization produced fresh yields equivalent to full autoclave sterilization — this method works.

The critical threshold is 140°F (60°C). Temperatures below this point for any portion of the treatment are insufficient to kill Trichoderma spores and competing bacteria, which is the most common cause of contamination failure in straw-based oyster mushroom cultivation.

→ Ready for Step 7 when the straw has been held at 160–165°F for a full, uninterrupted 60 minutes.

What You Need

• Pasteurized straw bags from Step 6
• Probe thermometer

What To Do

Remove bags from the water and allow the straw to drain and cool to below 75°F (24°C) — this typically takes 8–20 hours depending on ambient temperature.

Straw that is still warm when spawn is added will kill the mycelium on contact.

Once cool, perform the squeeze test: grab a large handful of drained straw and squeeze as hard as possible.

No more than 1 drop of water should emerge. If water streams out, drain further.

The target moisture content is approximately 65%. Too wet creates anaerobic conditions that favor bacterial rot, while too dry prevents efficient colonization.

→ Ready for Step 8 when the straw is below 75°F and the squeeze test produces no more than 1 drop of water.

What You Need

• Cooled, drained straw from Step 7
• Fully colonized grain spawn from Step 4
• Kitchen scale
• Large clean tub wiped with 70% IPA
• Rubber or nitrile gloves

What To Do

Work indoors in a clean area with no foot traffic and close windows to reduce airflow.

Wipe your work surface and mixing tub with 70% isopropyl alcohol. Weigh the cooled, drained straw and calculate spawn at 10% of the wet straw weight — for example, 20 lb (9 kg) of wet straw requires 2 lb (0.9 kg) of grain spawn.

A 10% spawn rate is recommended for beginners because it colonizes faster and reduces the window for contamination, though published research has shown biological efficiencies of 97.5% at a 6% rate.

Empty the straw into the disinfected tub, break up and add the weighed grain spawn, and mix thoroughly with gloved hands until spawn is evenly distributed throughout the straw.

Alternatively, you can skip the bulk mix and layer spawn and straw directly into bags in Step 9 — 2–3 inches of straw, a thin layer of spawn, repeating until the bag is full.

→ Ready for Step 9 when spawn is uniformly distributed throughout the straw with no large clumps of unmixed grain visible.

What You Need

• Straw/spawn mix from Step 8
• Polyethylene grow bags (25–30 cm × 50–60 cm)
• Zip ties or string

What To Do

Pack the straw and spawn mixture tightly into the polyethylene bags.

Press and compact firmly as you fill — the finished bag should feel like a firm pillow, dense and with minimal air pockets. Seal the top of each bag with a zip tie or string pulled tight.

→ Ready for Step 10 when all bags are firmly packed with no large air pockets and the tops are sealed.

What You Need

• Sealed bags from Step 9
• Sharp hole-punching tool (arrow tip, thick skewer, or razor blade)

What To Do

Using a clean, sharp tool, punch air holes in a diamond pattern approximately 4–6 inches apart across the bag body.

Make cross-cuts approximately ½ inch (1.2 cm) across. Create 10–15 holes per bag, distributed evenly up and down the bag.

These holes serve two purposes: they allow air exchange during colonization to prevent CO2 buildup, and they become the pinning sites where mushrooms will emerge through the plastic during fruiting.

→ Ready for Step 11 when each bag has 10–15 evenly spaced cross-cut holes in a diamond pattern.

What You Need

• Inoculated bags from Step 10
• Clean, dark room at 75–77°F (24–25°C)
• Probe thermometer
• Hygrometer (80–90% ambient RH recommended)

What To Do

Place bags in a clean, dark room at 75–77°F (24–25°C) with at least 3–4 inches of space between each bag. Monitor internal bag temperature with a probe thermometer every 24 hours.

Internal temperatures typically peak on Days 3–5 post-inoculation due to mycelial metabolic heat — if the room is at 77°F and the mycelium adds 15°F of metabolic heat, internal temperature can reach 92°F.

Spawn dies at 100°F (38°C), and temperatures above 90°F stress mycelium and favor bacterial contamination. If internal temperatures approach 88°F, increase spacing, reduce room temperature, or add airflow around the bags.

Leave bags undisturbed except for temperature checks. Full colonization on wheat straw typically takes 14–21 days.

Watch for green or blue-green patches, which indicate Trichoderma mold — any bag showing green coloration must be sealed in a trash bag and removed from the growing area immediately without opening indoors.

Yellow or brown patchy areas with no mycelium suggest bacterial contamination, often caused by overheating during pasteurization or inoculating straw that was still too warm.

→ Ready for Step 12 when uniform bright white mycelium is visible through all bag walls, the bag feels consolidated and firm, and no uncolonized straw remains.

What You Need

• Clear plastic storage tote, 50–90 L (64 qt), with lid
• Power drill with ¼" (6–8 mm) drill bit
• Coarse perlite
• Hygrometer/thermometer combo unit
• LED or fluorescent light, 6,500K

What To Do

Mark holes in a 2-inch (5 cm) grid on all six surfaces of the tote — all four sides, the bottom, and the lid. Drill ¼" holes at every marked point, creating approximately 100–200 holes depending on your tote size.

Rinse coarse perlite thoroughly in a colander until the water runs clear, then drain and fill the bottom of the tote with 3–4 inches (7.5–10 cm) of moist perlite.

Elevate the finished chamber on small legs or feet — wooden blocks or jar lids work — to allow airflow through the bottom holes.

The wet perlite releases moisture through evaporation to maintain 85–95% relative humidity passively. CO2, being heavier than air, settles toward the bottom and exits through the lower holes while fresh air enters from the upper holes.

Position a 6,500K LED or fluorescent light to deliver 500–1,000 lux at bag level on a timer set for 10–12 hours on and 12–14 hours off.

→ Ready for Step 13 when the chamber has holes drilled on all six sides, 3–4 inches of rinsed moist perlite on the bottom, and the light and hygrometer are in place.

What You Need

• Fully colonized bags from Step 11
• Shotgun Fruiting Chamber from Step 12
• Refrigerator (for optional cold shock)

What To Do

For Pearl or Grey Oyster strains (P. ostreatus), apply a cold shock before introducing fruiting conditions: place the fully colonized bags in a refrigerator at 2–10°C (35–50°F) for 12–24 hours, then move them into the fruiting chamber.

This simulates a natural seasonal temperature drop and signals the mycelium to shift from vegetative growth to reproductive fruiting mode. Do not cold shock Pink Oyster or Golden Oyster strains, which require warm fruiting temperatures.

Set the fruiting chamber environment to: air temperature 59–70°F (15–21°C) with 65°F as the optimal target, relative humidity 85–95%, CO2 below 800 ppm, and 500–1,000 lux of 6,500K light for 10–12 hours per day. These parameters must be maintained consistently from this point through harvest.

→ Ready for Step 14 when bags are placed inside the fruiting chamber and the hygrometer confirms 85%+ RH and 59–70°F air temperature.

What You Need

• Spray bottle with clean water
• Fruiting chamber with bags from Step 13

What To Do

Mist the interior walls of the fruiting chamber — not directly onto the bags or mycelium — 2–3 times per day to maintain 85–95% relative humidity.

Direct water on developing pins causes aborted growth.

Fan the chamber by removing the lid and waving it vigorously 1–2 times per day to flush CO2-rich air and replace it with fresh air.

Primordia (pins) appear at the holes in the bag as tiny 1–2 mm white or gray knots, typically within 5–14 days after moving to fruiting conditions.

If no pins appear after 3 weeks, check CO2 levels (elevated CO2 is the most common cause), confirm humidity is at or above 85%, verify that colonization was truly 100% complete, and increase fanning frequency.

Once clusters are visible, check twice daily — growth accelerates exponentially in the final 48 hours before harvest.

→ Ready for Step 15 when mushroom clusters are growing visibly from the bag holes, caps are expanding, and edges are still curled inward.

What You Need

• Mature mushroom clusters from Step 14
• Paper bags or paper towel-lined containers for storage

What To Do

Harvest when caps are 2–5 inches (5–12.5 cm) in diameter, broadly rounded, and the cap edges are still slightly curled inward. Do not wait until cap edges flatten or turn upward — once that happens, spore drop has begun and quality and shelf life decline rapidly.

A light dusting of white or pale gray powder on surfaces beneath the caps means spore release is already underway, so harvest immediately if you see it.

Harvest entire clusters at once when at least 50% of mushrooms in the cluster have reached harvest size.

Twist and pull the cluster at the base where it attaches to the substrate rather than cutting, because residual stem tissue left on the bag surface can become a contamination entry point.

After harvest, remove all substrate stump remnants from the bag holes. Refrigerate harvested mushrooms immediately at 1–4°C (33–39°F) in a paper bag or paper towel-lined container — never in airtight plastic, which traps moisture and accelerates sliminess. Stored this way, they keep for 4–7 days.

→ Ready for Step 16 when all mature clusters have been harvested and stump remnants cleaned from the bag holes.

What You Need

• Harvested substrate blocks from Step 15
• Container large enough to fully submerge the block
• Cool water (room temperature or refrigerator temperature)
• Weight to hold block submerged

What To Do

After first harvest, allow the substrate block to rest at ambient room temperature — not in the fruiting chamber — for 5–7 days.

Then rehydrate by submerging the entire block in cool water for 6–12 hours, weighting it down to stay fully submerged. 

Use cool or refrigerator-temperature water only — hot water will kill the mycelium. Do not soak beyond 12 hours, as extended submersion increases bacterial contamination risk.

Remove from water, drain for 1–2 hours, and return to the fruiting chamber under the same conditions as before.

Second-flush pins typically appear within 3–7 days. Second-flush yield is typically 40–60% of the first flush.

Most substrate blocks produce 2–4 total flushes before exhaustion, with a total productive life of 8–16 weeks from first inoculation.

When a block produces no pins after 3 weeks in fruiting conditions, feels soft, and begins to discolor, it is spent and can be composted.

→ Block is exhausted when no pins appear after 3+ weeks despite correct fruiting conditions and the block has softened and discolored.