Welcome to your King Oyster mushroom instructions - we're super excited to get you going.
You can get growing within three days of receipt, however, if you're not wanting to grow immediately you can put your kit in your fridge for up to one month, your mushroom may begin to grow even when chilled so get started asap.
Equipment needed: A water mister.
King Oyster mushrooms are top fruited.
Before Opening Your King Oyster kit, it’s important to check for good primordia growth – these are the tiny first stages of mushrooms that will develop into full-sized mushrooms once the kit is opened.
You can see the ‘Primordial’ bobbling on the surface.
This is what where your King Oyster Mushrooms will grow from, and important to establish these before you open your kit.
Your kit may need a few days to establish this growth before it’s ready.
On your King Oyster kit, the growth begins from the top of the block; once the primordia reach about 1–2 cm in height, your kit is ready to open and you can move on to the detailed instructions that follow.
How to get it started:
With clean scissors cut the very top off the grow bag leaving 10cm of bag above the top line of the substrate.
Mist the top surface of the substrate and loosely clip the opening together with a paper clip or peg. This will help prevent the top of the substrate from drying out whilst your mushrooms prepare to grow.
Mist inside your kit twice a day (up peg the top to mist) try not to let the substrate dry out.
Don’t worry if water begins to pool in places, on the top if your substrate, pour away the standing water if it begins to smother the top of your substrate.
Ideal growing temperature parameters are 17-22 degrees. Lower temperatures can lead to slower growth and higher temps can lead to the substrate and mushrooms drying out quicker.
As your King Oyster mushrooms grow larger in size, they may push against the sides, you can fold down the opening of the bag to release the mushrooms, letting them grow more freely.
When fully grown, you can harvest your mushrooms from the top of the kit as they mature, when the caps turn up and the mushrooms slow in growth. Do this with a sharp knife by slicing close to the base.
You may see some small mushrooms forming around the side of your kit. Once the top mushrooms have reached maturity and have been harvested, you can trim the grow bag to release the side forming mushrooms. They have grown here because of the humidity at the side of the kit.
It may be difficult to get a second harvest from a King Oyster grow kit. You may find sign of mould begin to form on your substrate block before any new mushrooms begin to establish. How ever we encourage you to try.
To do this you can close the top of the kit up and turn the substrate block upside down. Open the bottom of the kit - this is so you can attempt to grow a new flush of mushrooms from the base of the kit. Submerge the kit in clean cold water for 24 hours. The new surface should now be misted twice per day during the growing stage and until the new fruiting bodies fully mature.
Your substrate block should continue to smell fresh and healthy and looking well, with lots of healthy white mycelium growth all over.
When you have finished growing: Remove your substrate from the plastic bag - you can recycle the plastic at any large supermarket facility.
Your fruiting block should be left to dry out then disposed of into your household waste. We do not recommend composting or putting substrates into your garden, compost or food waste.
You can read more about this HERE.
- x -
Congratulations and we hope you enjoy your grow. If you have any questions or curiosities please do emails us at enquiries@caleybrothers.co.uk and we'll get back to you with 48 hours.
Otherwise, do feel free to take a look at other mushrooms you might enjoy growing and eating, we have a variety of options - all delicious and all just as easy to grow.
Where to next?
→ Get our book - Project Mushroom
→Join us online at one of our workshops this autumn
→ Follow us on Substack for new posts twice a month
Happy growing x
Ⓒ Caley Brothers 2026
