NORTH SPORE Black King Mushroom Grow Kit Fruiting Block

In stock
Regular price $30.00


Mushroom Grow Kit Fruiting Block

Black kings (Pleurotus spp.) -- also called black pearl kings -- are some of the heartiest mushrooms that can be cultivated. They offer the heartiness of a king trumpet, but with the growth style of a blue oyster. This hybrid has a neutral and savory flavor that lends itself well to many different cuisines and recipes. 

Black kings are less finicky than king trumpets and grow very well indoors. When cultivated successfully, you can expect a large harvest of very meaty and delicious mushrooms. However, they prefer cooler temperatures and are prone to drying out or stopping their growth if humidity is not maintained when the mushrooms are still in their early stages.

Skill level


Grow location


Grow speed

2 to 3 weeks

Shelf life

6 months (refrigerated)

Flavor profile

Umami, meaty, earthy

Kit dimensions

6in H x 9in W x 6in D

Kit weight

5 lbs



Your black king fruiting block kit is an amended sawdust block that has been completely colonized by mycelium. Before opening your bag at all, you should observe your block closely through the plastic. You want to watch for the development of baby mushrooms (also called 'pins' or 'pinsets').

Once your block has developed pins, you want to cut around the circumference of the bag one to two inches above the block while leaving a two-inch section uncut. This should allow the bag to form a clamshell-type enclosure around the block. You should be able to both cover the block with the bag and pull it back to reveal the block to the open air.

Black kings needs proper humidity and ventilation to survive. They especially love colder locations. Place your sliced bag in the most humid part of your home and away from direct sunlight.

We suggest putting your bag in a BoomRoom or on a kitchen counter somewhat close to a sink. The top of the bag that can clamshell open or closed will act as a humidity tent for your block. Think of it like maintaining a terrarium. Keep in mind that mushrooms exhale CO2 and inhale oxygen. They will suffocate themselves if there isn’t adequate airflow!

Harvest your black king mushrooms when they resemble the one in the photograph on the front of your kit! Harvest before the caps flatten out and become concave. They grow quickly, so when you spot your first mushroom pins, keep a close eye on them. The warmer the environment, the faster they will grow. Black king mushrooms should be ready to harvest three to seven days after pin formation.

Second flushes are somewhat difficult with black kings, but give it a try! We recommend giving your block a one-week break between fruitings. Simply leave it alone on your kitchen counter, soak your block in cold water for 20 minutes after one week, drain any water that may have become caught in the bag, and then restart the process of spraying your blocks with water daily.

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Temp, Humidity & CO2 guide:

Fruiting temps

55-70 degrees F



CO2 Sensitivity

<800 ppm

  • Fruiting - The phase of growth in which visible mushrooms begin to appear.
  • CO2 sensitivity - When CO2 levels are too high, yields will decrease, stems will become long and stringy, caps will be small, and/or growth will halt.


If you don't plan to use immediately, you can refrigerate your block for up to 6 months.


Black kings have a neutral and savory flavor that lends itself well to many different cuisines and recipes. When thinly sliced, they will sear nicely in a pan. With some grated Parmesan cheese, extra virgin olive oil, and fresh thyme, they make a great topping for pasta dishes.


Spawn used in our fruiting blocks is grown on USDA certified organic grain and made with organic cultures from our own culture bank. Our fruiting blocks are handmade from a blend of locally sourced, all-natural, organic, and non-GMO woods and supplements from farms and forests in New England and North America.

Creating a humidity tent:

If your home is really dry you may want to make a humidity tent to place over your bag. Simply take a trash bag or other loosely fitting plastic bag, put PLENTY of 1/2 inch holes in it. (THIS IS IMPORTANT mushrooms exhale CO2 and inhale Oxygen. They will suffocate themselves if there isn’t adequate airflow! Oysters that look stringy or strange are usually growing that way because they need more air!) If you choose to use a humidity tent make sure to spray the inside of the tent once per day to maintain humidity. 

Cautions & considerations:

If you’re going to consume home-grown mushrooms, make sure to cook your fresh mushrooms thoroughly with heat. If it is your first time eating this species, it is best to start with a small amount to check for allergies, even if cooked.

Mushrooms grow spores as they develop. This is a natural means of reproduction. This is when people with allergies or compromised immune systems may want to consider putting fruiting mushroom kits outdoors or in a well-ventilated area. Spores in mushrooms sometimes cause respiratory irritation.

In rare cases, spores may also cause irritation for some non-allergic or non-immunocompromised mushroom growers. If you are one of them, it is recommended to reduce the overall spore load by harvesting mushrooms while they are still in their younger growth stages.


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