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    How to grow king oyster mushrooms

    Pleurotus eryngii

    King oyster fruits on supplemented hardwood sawdust at 54–65°F (12–18°C), with a first harvest up to about 5 weeks after spawning. Its thick stems come from letting CO2 build up while the pins form.

    By Derick · October 24, 2026

    King oyster mushrooms with thick white stems and small flat tan caps, growing from the open top of a grow bag
    Fruiting temperature
    54–65°F (12–18°C)
    Humidity
    95–100% RH to pin, then 85–88%
    Spawn to first harvest
    Up to about 5 weeks
    Grows on
    Hardwood sawdust with 10–15% bran

    Difficulty: Moderate. King oyster pins are sensitive to swings in humidity and temperature, which makes it a bit harder than other oysters (GroCycle); North Spore rates it intermediate (North Spore booklet).

    King oyster growing conditions at a glance

    StageTemperatureHumidityFresh air / CO2LightDays
    Bulk colonization70–75°F (21–24°C)Sealed bagNone; bag stays sealedDarkAbout 14 days, up to 21
    PinningAbout 59°F (15°C)95–100%Corner of the bag cut; CO2 stays high insideIndirect light, or 12 hours a dayPins 4–8 days after opening
    Fruiting54–65°F (12–18°C)85–88%Bag cut back once pins are about 2 in; under 2,000 ppmIndirect light, or 12 hours a day4–5 days after the cut; picked within about 14 days of opening
    Where these numbers come from
    • Colonization: GroCycle incubates bags in the dark at 70–75°F (21–24°C) for about two weeks, and up to three (GroCycle).
    • Pinning: GroCycle drops the chamber to about 59°F (15°C) at 95–100% RH once a corner is cut. A kit forms pins 4–8 days after it's opened (GroCycle). North Spore lists "high CO2, keep in bag" for the pin stage (North Spore booklet).
    • Fruiting: GroCycle holds 54–65°F (12–18°C) and 85–88%, and harvests 4–5 days after the bag is cut back (GroCycle). North Spore gives 50–65°F, 85–95% and under 2,000 ppm for growing mushrooms (North Spore booklet).
    • Light: North Spore's booklet suggests indirect light, or artificial light 12 hours a day, for all its species (North Spore booklet).
    • The timeline rests on GroCycle, a company that sells growing kits and courses, as in our grow timeline guide.

    What does king oyster grow on?

    • Supplemented hardwood sawdust

      The usual choice: hardwood sawdust with 10–15% wheat or rice bran, hydrated to about 60% (field capacity) and sterilized (GroCycle).

    • Straw, cottonseed hulls, coffee grounds

      King oyster grows on these too, but GroCycle expects better yields from supplemented sawdust (GroCycle).

    • Outdoor bed of wood chips and straw

      Possible in a shady spot, but it can take six months to a year to fruit, and the mushrooms come out with short stems and big, dark caps (GroCycle).

    How to grow king oyster, step by step

    1. Mix and sterilize the substrate

      Mix hardwood sawdust with 10% bran and add water until a squeeze gives only a drop or two. GroCycle sterilizes the bags for three hours at 15 PSI (GroCycle). See sterilization vs pasteurization.

    2. Spawn the bags

      Mix in grain spawn at 2–10% of the wet substrate weight once the bags are at room temperature. More spawn colonizes faster (GroCycle).

    3. Incubate until solid white

      Keep bags dark at 70–75°F (21–24°C). Colonization is done when dense white mycelium covers the substrate, usually in about two weeks (GroCycle).

    4. Cut a corner and let it pin in the bag

      Cut a corner or a small slit near the top, drop the chamber to about 59°F (15°C) and hold 95–100% RH. Pins form inside the bag (GroCycle), where North Spore keeps CO2 high (North Spore booklet). GroCycle skips a casing layer, which adds work and contamination risk. Done when pins are about 2 in (5 cm) tall.

    5. Cut the bag back and fruit

      Cut the bag off level with the substrate, or leave about 4 in of sidewall as North Spore does (North Spore booklet). Hold 54–65°F and 85–88% (GroCycle). Done when the caps are about to flatten.

    What's different about growing king oyster?

    High CO2 makes the thick stems

    King oyster is grown for its stem, and CO2 is how growers get it. GroCycle fruits it in large grow bags with space above the substrate to hold CO2 high, for thick stems and small caps (GroCycle). North Spore keeps pins in the bag, then allows up to 2,000 ppm while they grow (North Spore booklet). That is far above the 600–800 ppm our CO2 guide gives for other oysters. Cornell Small Farms and Fungi Ally put king oyster among the species that tolerate 1,000–1,300 ppm (Cornell Small Farms and Fungi Ally).

    Too much CO2 shrinks the cap

    A Korean bottle trial grew king oyster at 1,600, 2,400 and 3,200 ppm. Caps on thinned bottles averaged 52 mm across at 1,600 ppm and 32 mm at 3,200, where caps grew narrower than the stems and some were misshapen. 2,400 ppm gave the best yield and quality (Ryu et al., Journal of Mushroom Science and Production).

    Thinning for bigger mushrooms

    Korean farms often thin each bottle to its best one or two young mushrooms. In the same trial, bottles thinned to one mushroom at 2.3–3 cm grew stems about 24% longer than unthinned bottles, around 122 mm against 98 mm (Ryu et al.).

    When and how do you harvest king oyster?

    Pick king oysters before the caps flatten and drop spores. Twist each one off at the base (GroCycle). Well grown, the stem can reach 8 in (20 cm) long and 2 in (5 cm) across (GroCycle).

    Expect fewer flushes than other oysters. GroCycle says a block can give two to three flushes, one to two weeks apart (GroCycle); North Spore expects one or two (North Spore booklet). Smallhold says royal trumpets are "trickier to second fruit" because they grow from the top of the block (Smallhold). Our second-flush guide covers resting and soaking.

    For yield, the Korean trial got about 100 g of mushrooms from each bottle of 580 g of moist sawdust substrate (Ryu et al.).

    Common king oyster problems

    Pins stall or abort

    King oyster pins abort when humidity or temperature swings (GroCycle). Keep the bag on until pins are about 2 in, and see why pins stop growing.

    Won't pin

    North Spore puts a slow block in the refrigerator for about eight hours, still in its bag, then returns it to the chamber (North Spore booklet).

    Dark spots on the caps

    This is likely bacterial blotch from water sitting on the caps. Improve airflow and stop wetting the mushrooms (GroCycle, North Spore booklet). See bacterial contamination.

    Tiny or misshapen caps

    CO2 is too high: in the Korean trial, 3,200 ppm gave caps narrower than the stems, and some misshapen ones (Ryu et al.). Add fresh air once pins are up.

    Tracking a king oyster grow in Hypha

    Hypha tracks each king oyster block from inoculation to harvest. It sets reminders from typical timings, so adjust a block's reminders if your bags need the full three weeks. The photo journal keeps each grow's pictures with side-by-side comparisons, which shows how stems change as you adjust fresh air. You can compare each strain's success and contamination rates.

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    King oyster growing FAQ

    How long does king oyster take to grow?

    King oyster takes up to about 5 weeks from spawning a bag to the first harvest: about two to three weeks to colonize, then up to about two more to fruit (GroCycle).

    Can you grow king oyster indoors?

    Yes, king oyster grows well indoors. Grow bags are the most popular way, and large farms use bottles. Indoors you can hold the CO2 that makes thick stems; outdoors it grows short stems and big caps (GroCycle).

    What temperature does king oyster need?

    King oyster colonizes at 70–75°F (21–24°C), pins at about 59°F (15°C) and fruits at 54–65°F (12–18°C) (GroCycle).

    Is king oyster hard to grow?

    King oyster is moderately hard: harder than blue oyster because its pins abort if humidity or temperature swings. Start with a ready-to-fruit block, or grow other oysters first, as GroCycle suggests (GroCycle).

    Sources

    1. GroCycle (grocycle.com/how-to-grow-king-oyster-mushrooms)
    2. North Spore booklet (cdn.shopify.com/s/files/1/2418/8179/files/FruitingBlockBooklet…)
    3. Cornell Small Farms and Fungi Ally (projects.sare.org/media/pdf/S/p/e/Specialty_Mushroom_Farm_Book__…)
    4. Ryu et al., Journal of Mushroom Science and Production (koreascience.kr/article/JAKO200514364645795.pdf)
    5. Smallhold (smallhold.com/blogs/blog-4/second-flushes-composting-best-pr…)

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