Organic King Oyster/Eryngii Mushroom Fruiting Block
Harvest your own king oyster mushrooms, also known as king trumpet, royal trumpet, or Pleurotus eryngii. This variety is prized for its thick stem, firm flesh, and dense texture — close to certain wild mushrooms like porcini.
- Variety: King Oyster, Pleurotus eryngii, king trumpet, royal trumpet
- Yield: between 0.75 and 1 kg (approx. 1.7–2.2 lb) of fresh mushrooms over 2 harvests, sometimes 3 in very good conditions
- Composition: wood sawdust, cereals including alfalfa, king oyster mycelium, lime
- Net weight: approx. 4.8 kg (about 10.6 lb)
- Dimensions: approx. 25 x 20 x 20 cm (about 10 x 8 x 8 in)
- Uses: cooking, pan-frying, grilling, risotto, stir-fry, preserving, or culinary processing
- Origin: Belgium ( La Mycosphère)
Download our instruction manual
Note: yield figures are estimates based on our production experience. They are not guaranteed, as productivity depends heavily on growing conditions: temperature, humidity, ventilation, light, and the grower's experience.
🍄 The variety: King Oyster
The king oyster is a more delicate mushroom to grow than classic oyster mushrooms, but it offers exceptional culinary quality. It generally produces less volume than a gray oyster, but its mushrooms are denser, firmer, and keep better.
Its standout feature is its wide, meaty stem, which is the most sought-after part of the mushroom. Its texture is firm, tender once cooked, with a mild, slightly nutty, umami flavor. It lends itself very well to pan-frying, grilling, thick vegetarian "scallop"-style slices, stir-fries, and slow-cooked dishes.
To grow beautiful king oysters, conditions need to be cooler and more stable than for oyster mushrooms. Fruiting is often slower, but the result is especially rewarding in the kitchen.
Our quality commitment
We produce our mycelium under laboratory conditions, ensuring varietal purity and optimal quality.
We produce our mycelium in a 100% organic way, and all our products are certified "BE-BIO-01, Agriculture Belgium" by CERTISYS.
📦 Using the fruiting block
Keep the block in the refrigerator if you can't use it right away, ideally for a maximum of 2 weeks. King oyster prefers cool conditions, so it's easier to grow in autumn, winter, or spring. In summer, choose the coolest spot possible.
For this variety, we recommend top fruiting — that is, with an opening on the top of the block. This method encourages vertical growth and the development of the thicker stems typical of king oyster.
- Stand the block upright in a bright room, but out of direct sunlight.
- Open the top of the bag above the substrate, without removing the plastic completely.
- Fold the edges of the bag slightly outward to create a clean opening on top.
- Keep the plastic around the block: it helps maintain humidity and limits drying of the substrate.
- Keep the surface of the substrate slightly moist until the young mushrooms appear.
- While the primordia are appearing, maintain high humidity, ideally around 90 to 95%.
- Once the mushrooms start to grow, reduce the humidity slightly, to around 85 to 90%, to avoid excess water on the mushrooms.
- Ventilate regularly, but without direct drafts: king oyster needs fresh air while keeping a humid, stable atmosphere.
Avoid wetting the young mushrooms directly. It's better to humidify the air around the block or the walls of a small growing chamber than to spray directly onto the primordia.
Use our minispray or our professional foggers to maintain enough humidity around the block.
⚙️ Growing parameters
| Fruiting temperature | 12–18°C (54–64°F). Ideal: 14–16°C (57–61°F) |
| Relative humidity | 90–95% at the start, then 85–90% during growth |
| Primordia appearance | About 7 to 14 days after opening, depending on conditions |
| Time to harvest | About 7 to 14 days after the young mushrooms appear |
| Ventilation / CO₂ | Moderate ventilation. Avoid stagnant air, but also dry drafts. |
| Light | Indirect light, about 500 to 1500 lux |
| Number of harvests | Usually 2 harvests, sometimes 3 in very good conditions |
Good to know: king oyster is very sensitive to growing conditions. A temperature that's too high or a lack of ventilation can produce thinner mushrooms with more developed caps and a less typical shape. Conversely, cool, humid, stable conditions favor thicker stems and better culinary quality.
🌱 Where to grow it
Grow your block indoors: a cool kitchen, cellar, garage, laundry room, or a lightly heated space. King oysters need a little light to form well, but you should avoid direct sunlight, radiators, and dry drafts.
The goal is to maintain a humid atmosphere around the block without soaking the mushrooms. A small grow greenhouse, a grow box, or a fruiting chamber can help keep humidity more stable.
🔄 Harvesting
Harvest king oysters when the stems are well developed, firm, and meaty, and the caps are still slightly domed. Avoid waiting until the caps flatten completely or curl up sharply: the texture then becomes less refined and storage life decreases.
To harvest, gently grasp the mushroom at the base and twist it off. You can also cut it cleanly at the base with a clean knife. Remove any leftover stems or old mushrooms to prepare for the next harvest.
The first harvest is usually the most abundant and the highest quality. The second harvest is often smaller but can still produce fine mushrooms if the block stays well hydrated.
📦 Storage
King oysters generally keep better than classic oyster mushrooms thanks to their dense flesh. Place them in a paper bag in the refrigerator and ideally use them within 7 to 14 days of harvest.
For longer storage, you can freeze them after cooking, dry them, or preserve them in jars according to your usual recipes.
Legal notice for Belgium: "Organic growing substrate: pasteurized and inoculated mushroom-farm substrate" (Derogation No. EM470.J). Do not consume the substrate.
🍳 Cooking tips
The king oyster is cooked whole: the stem is even the most sought-after part. Its dense texture lets you cut it into thick slices, lengthwise strips, or rounds.
For a simple preparation: slice the stems, sauté them over medium-high heat with a little oil or butter, then add salt, pepper, garlic, soy sauce, parsley, or fresh herbs at the end of cooking. Well seared, king oyster develops a firm, tender, and very flavorful texture.
💡 Tips for later harvests
After the first harvest, let the block rest for a few days while keeping humidity up. To encourage a second harvest, you can:
- Rehydrate the block by soaking it overnight in clean water, then drain it well before returning it to cultivation
- Apply a light cold shock by placing the block in a cool spot overnight — in the refrigerator or a cold room
- Check that the surface of the substrate hasn't dried out
- Maintain high humidity, without wetting the young mushrooms directly
A side opening, as used for oyster mushrooms, is possible but isn't our recommended method for king oyster. It can give mushrooms closer to a classic oyster, with more developed caps and less thick stems.
Legal notice for Belgium: "Organic growing substrate: pasteurized and inoculated mushroom-farm substrate" (Derogation No. EM470.J). Do not consume the substrate.
Frequently Asked Questions
