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King Oyster Mushroom Growing Profile

Introduction

As befitting their name, King Oyster Mushrooms are the largest of the Oyster family, with a single fruit weighing in well over 1 pound. With their brown, stout cap and thick white stem, these fungi can grow up to 8 inches long and 2 inches wide, and their distinctive shape has earned them the nicknames King Trumpet, French Horn, and Royal Trumpet.

While other Oyster mushroom species tend to grow in shelf-like formations with the fruit jutting out from the side, King Oyster Mushrooms are a “top-fruiting” species, with the cap flattening as it grows.

With a little care and the correct cultivation techniques, it is possible to grow King Oyster Mushrooms both indoors and outdoors, throughout the year. If you do decide to grow indoors, and if they are given too much fresh air and bright light, the stem will be too small and the cap too large, whereas high levels of CO2 during the cultivation period will ensure fat, juicy stems, and smaller caps. This is considered more desirable from a culinary point of view and perfect for growing indoors.

Their meaty fruit offers an appealing texture with a bold, nutty flavor that sweetens as it is cooked. Highly versatile, the strong texture will even hold together with a little barbequing!

Habitat of King Oyster Mushrooms

Native to southern Europe, the Mediterranean, and North Africa, King Oyster Mushrooms grow naturally amongst and upon the roots of hardwood trees, emerging from the surrounding soil.

Most members of the genus Pleurotus will act as saprotrophs, meaning that they digest and process the decaying organic matter, breaking up the deadwood and returning nutritious minerals to the ecosystem; however, King Oyster Mushrooms are also weak parasites, feeding off the still-living roots of herbaceous plants. They may be cultivated on organic waste matter too, as described below.

Spawning Details for King Oyster Mushrooms

King Oyster Mushrooms are vigorous growers, they can take 1 to 2 weeks to spawn and pin. Temperatures for spawning should be approximately 68-7F or 20-22C, and a spawn run takes between 10 to 14 days. Mix you’re spawn in with a cellulose rich substrate which has been sterilized or pasteurized.

When grown outdoors, King Oyster Mushrooms can be cultivated in raised beds, lined with cardboard, and filled with layers of spawn. Either hardwood sawdust, woodchip, or chopped cereal straw can be used. For a 1m square bed, 15cm deep, 1kg of sawdust spawn should be plenty.

Indoors, King Oyster Mushrooms can be cultivated on a wide range of organic matter: hay, straw, sawdust, spent coffee grounds. For beginners, one easy method is to use a monotub, as King Oyster Mushrooms flourish in high CO2 environments, something monotubs can easily create.

As with other Oyster Mushroom varieties, rye grain spawn is the best choice, although you can also use millet or wild birdseed. Grain spawn is made from sterilized grains that have been inoculated with live mycelium culture; this gives the growing fungi an added energy boost.

One slightly different approach with King Oyster Mushrooms is that the mushrooms can be spawned inside a spawn bag that does not have to be folded flat. This is because King Oyster Mushrooms are top-fruiting, and so we want space to be able to encourage the fruit to blossom at the top. Keeping the bag lightly sealed will retain the CO2 produced by the emerging fungi, which will, in turn, lead to thick, meaty stems and smaller caps over time, this is the desirable fruit for King Oyster Mushrooms. Only unseal the bag after pins have begun forming.

Pinning Conditions for King Oyster Mushrooms

King Oyster Mushrooms are usually quite aggressive when it comes to pinning. Due to this it is possible to keep your cultivation bag or container closed until pins, or primordia (baby mushrooms), have formed.  Decrease the temperature for the pinning stage to below 60F or 15C, with humidity around 80%. Increase the supply of fresh air (by opening the bag up occasionally) to allow development of pins.

As explained above, the increased CO2 levels will ensure a better growth of your King Oyster Mushrooms, and the high humidity will also encourage pin formation.

If you decide to use a cultivation bag, remove or open only the top of the bag. This will allow the top-fruiting mushrooms space to emerge, and the enclosed sides of the bag will help trap CO2, perfect for developing thicker fruiting stems with smaller caps.

A casing layer may also be used to encourage formation of King Oyster Mushrooms pins; however, this is completely optional. This layer is applied to the fully spawned surface of the mushrooms, increasing humidity, and therefore improving the yield and quality of the fruiting fungus.

However, using a casing layer does carry the risk of contamination. To avoid this risk, you can instead scratch the surface of your growing mushrooms. Without opening the bag (and therefore letting that precious CO2 escape!), lightly scratch against the surface of the substrate, creating grooves just right for the formation of pins.

If you do wish to use a casing layer, use a mixture of 50% coco-coir and 50% vermiculite, along with 1% hydrated lime, rehydrated with boiling water. Only use once fully cooled to room temperature.

Personally, I think people growing King Oyster mushrooms at home shouldn’t worry about casing the substrate. It creates an added factor to worry about which isn’t really necessary, work on creating a good pinning environment instead.

Fruiting Conditions for King Oyster Mushrooms

Fruiting conditions require temperatures between 59-64F or 15-18C, with humidity reduced to a minimum of 80% and maximum 90%.

King Oyster Mushrooms tend to create tastier fruits in high CO2 environments, which is great news for home cultivators. The time taken to fruit will depend on both temperature and humidity. 

The Best Substrate for growing King Oyster Mushrooms

King Oyster Mushrooms are found growing in the wild on dead and decaying hardwood, as well as living herbaceous plants. For cultivation purposes, they can be grown on several surfaces, including any material rich in cellulose, such as hay, sugar cane mulch, and corn cob, while pasteurized blocks of sawdust or straw bales are also good options, especially if you are hoping for multiple harvests.

However, sterilized hardwood substrate or a supplemented mix are guaranteed to produce much higher yields and better quality fruits.

When to harvest King Oyster Mushrooms?

Like many mushrooms, King Oysters are best harvested while still young for a better taste. However, if you are looking forward to having a thick, meaty stem to add great texture to your dish, then it is advisable to let the mushrooms grow a little longer. These stems are less fibrous than those of other mushrooms, which makes them more palatable.

To harvest, cut the mushroom at the base of the stem with a sharp knife. If you don’t want to eat your harvest yet, try and keep your King Oyster Mushrooms in a cluster. They will keep for up to 10 days in a fridge, and you can also use a dehydrator to preserve for 6 months.

Fruiting Containers for King Oyster Mushrooms

Grow bags are perhaps the easiest fruiting container for beginners, with the top left open to allow the fruits to grow. The humid microclimate created in the top of the bag is perfect for King Oyster Mushrooms as the constant humidity will lead to a reliable yield and the high CO2 levels will produce thick stems. 

King Oyster Mushrooms also grow reliable in monotubs and other basic containers wherein the humidity can be kept high. This is due to the fact that CO2 buildup is not a concern with King Oyster Mushrooms.

Finally, there is the rather interesting option of growing out of the top of jars or bottles – this will lead to cylindrical-shaped mushrooms with a very small cap.

Yield of King Oyster Mushrooms

King Oyster Mushrooms offer a yield of up to 1 to 2kg per square metre. Those mushrooms cultivated in high CO2 conditions will have long, thick stems and small caps; as the stem is the tastiest part of the King Oyster, it is therefore best to have as high a CO2 level as possible throughout the growing period.

What do King Oyster Mushrooms taste like?

Whilst having a pleasant nutty flavor, King Oyster Mushrooms are famed for their highly respected texture. With a soft, non-fibrous stem, they can either be prepared whole or cut into smaller slices to suit the dish. Sliced into steaks and allowed to slowly simmer in a casserole or stew is a mouth-watering way to bring out the meaty texture; marinating in butter and herbs, before wrapping in foil and roasting is another delicious recipe.

Other methods include frying and grilling, and they make a good substitute for any mild-flavored meats. Crumbled King Oyster Mushrooms are a particular delicacy, especially when added to soups.

Oyster mushrooms have some of the highest-fiber content of any fungus, with King Oysters also offering a good source of niacin (vitamin B3), riboflavin (vitamin B2, necessary for cell growth and function), and vitamin D (necessary for healthy bone density). They can also play a role in reducing cholesterol and are a good, low-calorie option for snacks.

Are King Oyster Mushrooms low fodmap?

Yes! All Oyster Mushrooms are considered a low fodmap food source.