Grow mushrooms the EZ way.

How To Grow King Oyster Mushrooms.

King Oyster mushrooms are one of my favorite mushrooms to grow at home, the fruiting bodies develop fast producing large thick stems all of which are great fun to watch develop day to day.

The best thing about growing King Oyster mushrooms is these mushrooms can be grown indoors using several different methods such as monotubs and jars.

When grown inside they produce thick stems due to the Co2 levels indoors which is ideal for what we want from this species.

King Oyster Mushrooms are fairly easy to grow at home, although the need for cold shocking, cold growing conditions and casing layers may make them harder than other oyster varieties.

It is important to ensure you don't over mist them as they are highly susceptible to blotch.

They also require a cold environment to grow so King Oysters project should be done during your winter time.

Unlike my post on King Oyster Mushroom growing profile, here, I will provide a step-by-step guide on how to grow king oyster mushrooms at home.

King Oysters At A Glance.

Best Substrates For King Oysters: Hardwood Sawdust (Oak, Aspen, Beech, HWFP), Coco Coir, Supplemented Straw.

Spawn Creation: Temperatures 20-22c, Time Approximately 10-25 days.

Incubation:  Temperatures 20-22c, Time Approximately 5-7 days. 

Fruit Development: Temperature 5-10c, Time Approximately 5-7 days

Full Grow Time: 6-8 weeks (this really depends on spawn quality and amount used).

Casing Layer Requirements: Smaller surface areas will require a casing layer, larger fruiting surfaces can get away without one.

How To Grow King Oyster Mushrooms At Home.

This post is going to assume you already have King Oyster Grain or Sawdust spawn, this can be purchased online or you can make it yourself by following my post “how to make grain spawn“. 

Step 1 – Gather Supplies.

King Oyster mushroom grain spawn. 

As discussed previously, here is a post on how to make grain. This can also be purchased as sawdust spawn from a reputable spawn provider which i would recommend if you are after quicker results.

Bulk substrate (read what is a bulk substrate).

King oyster mushrooms grow on and decompose hardwood in the wild so you can use: hardwood fuel pellets, hardwood sawdust, straw, and even flourish on coco coir.

Instant Pot.

I will be using my Instant Pot to pasteurize my bulk substrate using the hot water bath method, this is an optional item that makes the process easier, however, if you have a stove, large pan and a thermometer you can just use those instead.

Checkout how to pasteurize bulk substrate for a full breakdown of other techniques you can use.

Plastic Container.

This will be used for fruiting the King Oyster Mushrooms, try to get the biggest one possible so the mushrooms have plenty of nutrients to grow BIG. I am going to demonstrate two grows in this post, this will help to manage expectations on how much substrate is required for a good sized harvest. The container I will be using are one large (11L unmodified container), one small (5L unmodified container).

Alcohol, Rubber gloves, and Face Mask.

These will be used to minimize contaminants being entered into the spawn during the mixing process. Not absolutely necessary (you could wash your hands and container with soap) although good to use anyway.

Net Bags OR Pillow Case.

These will be used to keep the bulk substrate together during the pasteurization process.

Step 2 – Pasteurize The Bulk Substrate.

Weigh out enough bulk substrate to fill your plastic container leaving about a 1-inch gap at the top.

Container with bulk substrate.

Next, place the bulk substrate in a net bag.

Place the net bag into the Instant pot.

Substrate for King Oysters in Instant Pot

Fill the pot up with water until the substrate is completely submerged in water. 

Pasteurizing substrate instant pot

Using the sous vide setting, set a temperature to 168F (76c), set the timer for 2 hours, finally press start (if you are using a stove and thermometer then just heat the water to 160-168F degrees and maintain, then add you net bag).

One of the benefits of using an instant pot or a sous vide (checkout my discussion on both) is you can set the tempretures and forget about it until finished.

Setting temperature for instant pot

Come back regularly to check the internal temperature of the substrate using a thermometer if your using a stove.

When done, carefully remove the substrate net bag from the pot and allow it to cool and drain.

Step 3 – Spawn King Oyster Spawn To Bulk Substrate.

Put some rubber gloves and a face mask on. Wipe down your gloves with rubbing alcohol.

Next, wipe down the inside of your large container with alcohol and set that aside to dry.

Take the king oyster grain spawn jar, wrap it in an oven glove and bash it on a bike tyre or football or similar.

If you are using sawdust spawn crush it into pieces in the bag.

Next mix about 3 x 800ml jars grain spawn jars into the pasteurized substrate inside the 5L container you are going to be using.

Double the amount of spawn if you are using a larger 11L container.

Pat down the substrate lightly until it has an even surface on the top.

Finally, wipe any excess substrate off the edges of the container and put the lid on.

Step 4 – Incubate (Leave it alone).

Place the container somewhere it won't be disturbed like a cupboard with temperatures at 70-75F (21c – 23c).

Check the container every couple of days for any signs of contamination, if you see anything then get rid of it immediately.

Wait until the bulk substrate is 100% colonized (this is when white mycelium completely engulfs the bulk substrate) like this.

Step 5 – Fruiting King Oyster Mushrooms.

When you start to see small white knots appear on the surface this means your container is ready to fruit.

In the picture below I am actually a bit late, pinning has started around the edge of the box, no worries.

Mushroom Primodia

Depending on the size of the container it might be worth adding a casing layer (read about how to make a casing layer) to the top of the substrate to aid in the fruiting process.

If I am using a large container which holds around 11L of substrate, I won't bother with casing.

However if I am using a smaller 5L container I normally add a casing layer to avoid the substrate drying out and maintain hydration levels on the surface.

Cased Shoe Box Grow

To trigger King Oyster mushroom fruiting, place the growing vessel in temperatures of 2-5c for a day or two (I put my small container in the fridge), this should cause a “cold shock” which should trigger the initial fruiting process.

For larger containers I pop them in my garage or a room without the heating on for a couple of days. Normally a couple of cold nights will initiate pinning.

Fruiting King Oysters

Wait at least 7 days and you should start to see mushrooms forming.

Leave the lid on until you start seeing mushrooms forming from the substrate, I then pop the lid off and place it on top with a small gap until the mushrooms start getting larger.

King Oyster Primordial

Eventually I completely remove the lid.

Growing King Oyster Mushrooms

Once the King Oyster mushrooms have started to grow larger begin to mist them with water once a day. 

You just want little droplets left on the substrate, if the mushrooms already have droplets on them DO NOT MIST (see picture below).

Do not over mist King Oyster Mushrooms or you risk blotch infecting them. 

Once the mushrooms have began to enlarge they will quickly soak up lots of water including all those droplets.


Here I am going to compare the grow and harvest of the 5L container in comparison to the 11L container.

The small grow was fun but really didnt produce much of a worthy harvest, however the 11L container did really well and I had an easier time getting it to fruit.

5L Container Harvest.

Small amount of King Oyster Mushrooms

11L Container Harvest.

I took two flushes from this box, initially I went on holiday for 3 days and took what I could (too early really) then when I returned the small ones I left over blew up. 

Commercial farmers will often crop away smaller fruits to allow for a few large fruits so this is probably why my second flush was larger.

King Oyster mushrooms in bowl
Larger King Oyster Harvest
Large King Oyster Mushroom
King Oyster mushroom growing

How do I Harvest my Mushrooms?

You can either cut the stem at the very bottom with a sterilised knife or twist and pull the mushrooms of the substrate. Then store them inside a paper bag in the fridge (or something else which won't create condensation).

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