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Black pearl king oyster mushroom Fruiting blocks!

You can purchase one from us here!


Blue Sky Fungi Black Pearl King Oyster fruiting blocks are made of fully colonized hardwood sawdust and small wood chips that are supplemented with wheat bran and gypsum.

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Special Note: Do not open your mushroom fruiting block until you have read through ALL these instructions and prepared all the necessary materials. The Black Pearl King Oyster mycelium (the fungi that forms the mushroom) is the white organism that is growing on the sawdust block. Before you begin, make sure that the mycelium block was not cracked or broken apart within the bag. If the block is cracked, place the sealed bag in a dark place and don’t move it around. Allow the mycelium to recover and regrow for a few days undisturbed. If it starts growing clusters of tiny mushrooms within the bag, it is ready.

ALWAYS!!! use non-chlorinated water to keep the mycelium moist. Well water is good, but if your tap water is chlorinated, you can use filtered water or leave an open container of water out overnight to dissipate out the chlorine naturally

Placement Indoors: Find a place inside that is of average room temperature, has indirect lighting (enough to read words on a page, but not in direct sunlight), and away from drafty air currents, fans,  heat sources, and materials that are porous like wood surfaces or carpets (spores drop from the mushroom). A more humid place like a basement is better than a really dry place. You will place a humidity tent (a plastic bag with air holes cut out of it) over and around the block to maintain a high humidity environment. We recommend you place the block on a plate or pan to catch the water that drips off the side of the humidity tent.

Use of a Humidity Tent: Sometimes a location will require the use of a humidity tent, which is basically an oversized plastic bag with many holes. The idea is to make an environment that holds humidity/moisture and will allow fresh air to enter (and CO2 to exit). You do not want the humidity tent to be touching the mushroom, but rather creating an environment around the mushroom. The humidity in the tent can be maintained with a spray bottle. Lift up the tent/bag and spray the fruiting block and the inside of the plastic bag so it appears moist and water droplets are visible, or you can just spray through the holes in the plastic bag.

Do this 2 to 3 times a day (or more if warm, dry conditions exist). Place a pie-pan or broiler pan under the fruiting block to collect the water.

black pearl king oyster (pleurotus ostreatus - hybrid)


Temperature: 50 to 75 degrees F        Humidity:  90 to 100 %

The Black Pearl Oyster mycelium will be the thick white growth that is growing on the sawdust block. If it starts growing clusters of tiny mushrooms within the bag, it is ready.

The block can be initiated without mushrooms forming.

Setting Up and Initiating Fruiting: Prepare the space you would like your Black Pearl Oyster to grow in. The block will remain in the plastic grow bag during the growth process and mushrooms will grow from the surface of the block out of a long slice in the side of the bag or out from the top surface of the block. To determine where to make the opening, look for clusters of little pin-shaped mushrooms growing on the surface of the sawdust block, these are the primordia of the mushrooms. If you see the clusters on the top surface, cut the entire top of the bag off with scissors or a razor blade, to about 2 inches from the top of the block. If you see the clusters forming on the sides, cut the plastic around them with a razor blade to expose them to fresh air. If no primordia clusters have formed, you can direct the mushroom growth out of the cut you make. Either cut the top off (as detailed above) or make a 3-inch-long, horizontal slice in the side of the plastic grow bag. If the primordia has grown large and deformed within the grow bag, you may open the bag to remove the mushroom, which will restart the growing cycle for a new mushroom. To do this, cut the top seal of the bag open with scissors so you can reach in with clean hands to pull off (or cut off) the mushroom mass. Then roll the bag shut to remove as much air space as possible and make a long slice in the side of the bag. Black Pearl Oyster mushrooms will grow out of the hole toward the fresh air and expand once outside the bag. Oyster mushrooms are phototropic (grow toward light), so you may want to adjust the orientation of the block so that the opening is pointing toward the light in the room.

When everything is set up, follow these steps:

  • Clean your hands and the scissors or razor blade.

  • Determine the site where you want the mushroom to grow and cut the plastic or cut the plastic around the already growing mushrooms.

  • Gently squeeze the excess air out of the bag and fold the top portion over. You can tape down the bag flap to keep it tight against the block, or you can turn the bag on its side to pinch down the plastic flap.

  • Place the humidity tent (plastic bag) over and around the entire mushroom block and the plate and/or support object under the block. You should spray the inside of the bag with a water mist from a spray bottle prior to covering the block with the humidity tent.

Daily Care: Now that your mushroom fruiting block is set up, you need to perform some daily care.

  • Maintain a high humidity environment within the humidity tent. There should be visible droplets of water on the inside of the humidity tent and on the grow block plastic. Do this with the spray bottle several times (2 to 4) per day. Also, mist the mushroom primordia and the exposed surface of the block.

  • Allow for good airflow. There should be enough holes in the humidity tent to allow fresh air exchange and maintain the humidity for several hours. The humidity tent can also be removed and replaced each time you mist to promote air exchange.

  • It is recommended to carefully remove the bag each time you spray the inside of the bag with the spray bottle, then carefully replace the humidity tent to create an open pocket around the growing mushroom. Try to avoid allowing the plastic humidity tent to touch the growing mushroom. (Remember to use non-chlorinated water or breathe off the chlorine first)

Growing: Black Pearl Oyster mushrooms should start to grow within 2 weeks after opening the bag and take about 1 week to grow. You may see other clusters of mushroom primordia forming under the plastic of other areas of the grow bag; you can cut away the plastic on those to allow them to grow. Continue to water the humidity tent while it has mushrooms growing but try to avoid getting a lot of water onto the underside of the developed mushroom caps. The cap of the Black Pearl Oyster will be an ashy gray color with black spots, while the stem should be white.

Harvesting: The mushrooms are ready to harvest when the cap is still curled downward. As the mushroom matures, the cap will flatten out and is dropping spores at that point. The quality of the mushroom will begin to degrade after the cap has flattened. You can harvest the mushroom by cutting it off at the base of the stem and flush with the surface of the block. Younger mushrooms are denser and will have a better shelf-life than an older, flat-capped mushroom. Always cook your mushrooms prior to eating.


Don’t get rid of the block. The Black Pearl Oyster will produce another flush of mushrooms, but you will need maintain the humidity in the tent to promote adequate growing conditions.

You can expect at least 2 flushes of mushrooms from these blocks. If the block seems very light a few days after you harvested the first mushrooms, soaking the block for an hour or two can stimulate more growth. If the bag is still intact and you cut the top off, add about a pint of water to the bag. About 1 week after the harvest, search the sides of the bag for primordia clusters forming within the still-intact plastic areas of the grow bag and cut the plastic around them. If no more mushrooms form, or you cannot provide adequate daily care, then you can try to place the block outside to grow in the spring or fall weather. Just make sure to keep it in a humid environment and out of direct sunlight. If to no avail, then the block will make excellent mulch or compost for your garden.

For a PDF copy of the Black Pearl King Oyster Fruiting Block Instructions, click here.

frequently asked questions

Mycelium require certain conditions to produce a mushroom. These conditions include specific temperature, humidity levels, CO2, and light. Many problems encountered with growing mushrooms are a result of an imbalance of these conditions. The solution is to manipulate the environment to be favorable for the mushroom to produce and survive. The following section will answer some frequently asked questions about growing Shiitake mushrooms from a Blue Sky Fungi fruiting block.

The block is not producing mushrooms and feels light and dry.

This is most likely a problem of humidity and available water. You should be misting the block and humidity tent at least once a day, but if your growing environment is too dry, you may need to hydrate it more than that. Always use a humidity tent for Black Pearl Oysters. Remember to always use non-chlorinated water! You can also soak the block in a bucket of water for an hour or two to stimulate more mushrooms to grow. Or if the top of the bag is removed and the bottom portion of the bag is still intact, add a pint of water to the bag.

I am hydrating the block daily but the mushrooms still won't grow.

This is might be a problem of temperature. Make sure it is not too cold or too hot where the block is placed. Also make sure that the block is not placed in direct sunlight.

There are a lot of clusters of tiny mushrooms forming under the plastic.

If the block is not opened and it is more then two months beyond the date on the bag, the mycelium will start forming mushroom primordia wherever it can. If you cut the plastic around all of the tiny mushrooms, the majority of the mycelium will be exposed to air. This will cause a lot of smaller mushrooms to form and the mycelium has a greater chance of drying out. It is better to select one or two areas to cut open and allow the mushrooms to grow out of those. The other small mushrooms will abort and the majority of the energy will be directed to the mushrooms near the cuts in the bag. Squeeze the air out of the rest of the bag and leave the cut portion exposed to the fresh air and pointing at the light in the room.

It looks like bacteria or mold is growing on the surface of the block.

Competitor organisms are everywhere and opportunistic. It is not uncommon that small blotches of bacteria or mold will grow on the surface. Bacteria and molds are generally shades of green, yellow, blue, spotty white, and black. Lion's Mane will look white. Use hydrogen peroxide or very dilute bleach dabbed gently on the infected areas. You can scrape off infected spots with a paper towel after treating them with peroxide. If the surface contamination cannot be overcome, it may be time to retire the block to the outdoors. You can set it outside in a shady spot and allow it to get wet. The outdoor conditions may be favorable for mushrooms to continue to grow.

Is it safe to eat the mushrooms if mold is growing on the block?

Short answer is: yes, if you are cooking the mushrooms. This is one of the many reasons why it is important to cook all mushrooms. Most of the time the infection is growing on the skin of the block and is benign to the mushroom. If the mold or bacteria has spread to the mushrooms, then probably not, but mushrooms in the wild generally will host a community of organisms. If you are in doubt, compost the mushrooms, clean the block, then try again.

What if the block breaks within the plastic bag?

This is no big deal as the mycelium will heal itself back together. However, if a significant crack in the block has resulted from transport or an accidental drop, allow the block a few days to recover and heal itself within the bag prior to opening.

What if I go away for a few days or weeks while I'm growing the mushrooms?

Harvest the mushrooms before you leave and let the block stay in a humid environment. This may have to be outside if the temperatures are not too cold or too hot. It is not advised to bring the block back inside for growing, as it may be a new home for bugs. And you don't want those could be your new house bugs.

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