How to grow your King Oyster grow kit
This guide takes you step by step through your first – and every following – harvest. King oysters are thick, nutty and resemble porcini in texture.
Important: storage before you start
As long as your grow kit is unopened, store it in a cool, dry, frost-free place below 20 °C. Check the best-before date – the kit should be activated by then.
Step by step to your harvest
1. Set up the kit
Find the most humid spot you can – a bathroom or cellar usually works best. Ideal are 15–20 °C and around 90 % humidity.
2. Cut an opening
Cut an opening of about 5 cm above the white air filter.
3. The first mushrooms appear
As soon as small mushrooms of 4–5 cm appear on top of or at the side of the block, cut the foil all the way round with a sharp knife or scissors and carefully pull the upper half of the bag off. The top half of the block is now exposed; the bottom half stays protected by the foil.
Tip: no room with enough humidity? A large plastic bag or bin liner over the kit creates ideal conditions.
4. Growth phase
Your mushrooms are now growing – make sure the kit doesn't dry out. If the kit or the mushrooms feel dry, moisten them with fresh, cold tap water from a shower head. Less is more: avoid waterlogging around the block. Pour off any water that collects in the bag.
Please note: don't use a plant sprayer – germs can build up inside and harm the mycelium.
5. Harvest
King oysters are ready once they stop visibly growing and the cap edges of the largest mushrooms have almost fully opened. Always harvest the whole flush at once – smaller mushrooms stop growing once part of the harvest is removed. Then remove all stem remains from the block.
6. More flushes
Give your kit a rest of about 2–3 weeks in an airy spot and water it with the shower head every 2–3 days, without waterlogging. For the next flush, submerge the kit completely in fresh, cold tap water for 4–5 hours, then set it up again at 15–20 °C. One kit gives you 1–2 flushes.
And afterwards? A spent kit is far too good to throw away: remove the foil and add it to your compost or organic waste bin as a valuable organic fertiliser.
Ideal conditions for King Oysters
Fruiting initiation
- Temperature10–15 °C
- Humidity95–97 %
During fruiting
- Temperature15–21 °C
- Humidity85–90 %
- Fresh air (CO₂)< 1200 ppm
- Light500–1000 Lux, indirect
Values from the book “Faszination Pilzzucht” by Sebastian Reindl (Stocker Verlag) and from our own practice at our mushroom farm in Schleedorf, Austria.
Troubleshooting
Long stems, stunted caps
King oysters need little fresh air for thick stems – but with too little fresh air the caps become stunted. Air the room now and then or open the bag briefly.
Water standing in the bag
Pour off the water and water less. The block should be moist, not wet.
No growth, or only weak growth?
Have a look at our FAQ or get in touch via our contact form – ideally with a photo. We are happy to help.
Enjoying your King Oysters
You can recognise fresh king oysters by the squeeze test: the stem clearly resists pressure between two fingers. Sliced and seared, grilled or cut into “scallops” from the stem, they are a treat. More tips in How to grow king oyster mushrooms.
FAQ about the King Oyster grow kit
Why harvest the whole flush at once?
As soon as part of the mushrooms is removed, the smaller ones stop growing. So always harvest them all together.
How do I stop the kit drying out?
Moisten it regularly with a shower head or put a large plastic bag over it as a mini greenhouse.
Why aren't new mushrooms forming?
After each harvest the kit needs 2–3 weeks of rest and then a 4–5-hour water bath as a start signal.
How do I store the kit before starting?
Cool, dry and frost-free below 20 °C – and activate it before the best-before date.
How do I store harvested King Oysters?
They keep for several days in the fridge – longer than most other gourmet mushrooms.
Want more?
Reorder directly from us, discover more mushroom species or learn how to grow mushrooms yourself in one of our courses.
Questions? FAQ · Contact · All guides
