How to Grow Black Pearl Oyster Mushrooms with a Grow Kit

Black Pearl Oyster mushrooms are a great choice for growers who want something a little different from the classic oyster varieties. They produce dense, meaty clusters with a rich, savory flavor and an attractive dark cap, making them especially rewarding to grow and cook with. This particular mushroom combines the clustered growth habit of an oyster mushroom with the thick stems and substantial texture associated with King Oyster mushrooms.

They prefer cooler fruiting conditions and do best when humidity and fresh air stay consistent. They’re a rewarding choice for experienced growers who want an impressive mushroom that is still straightforward to fruit at home.

Your Redwood Mushroom Supply block arrives fully colonized and ready to fruit. Black Pearl Oyster mushrooms are top-fruiting mushrooms. Keep the sides of the bag intact and fruit from the top of the block. They prefer cool conditions, high humidity, indirect light, and gentle steady fresh air.

Growing Guides, Ready-to-Fruit Blocks

How to get started

Open the Top of the Bag

Keep the block inside its original plastic grow bag. Black Pearl uses the plastic above the block as a humidity collar, so do not remove the bag and do not make a side X or slit.

Make sure to start with clean hands or wear clean gloves. Stand the block upright.
Use clean scissors to cut off the top of the bag ABOVE the filter patch.
Leave at least 6 inches of plastic above the substrate.

The remaining plastic acts as a humidity collar. It helps keep the air around the top of the block humid while the mushrooms begin to pin.

Control the Humidity and Watch for Pins

Black Pearl should fruit from the top of the block. Monitor for small pins pressing against the plastic at the top of the bag.

A. Growing in an Automated Mushroom Tent

Place the open block in the directly in the tent and wait until you see small white bumps, knobs, or young mushrooms pressing against the plastic near the top of the block. These are pins. Keeping the bag closed during this early stage helps the block hold humidity. Aim for 50–62°F and humidity level between 85–95%. Make sure to provide steady fresh-air exchange and avoid pointing a fan directly at the block.

B. Growing on the Countertop:

Place the opened block in a cool room (best temperature between 50-62°F) with indirect light and wait to see pinning. If your room is dry, loosely place a clean plastic bag over the entire kit as a humidity tent. Leave the bottom of the humidity tent loose, or add a few small holes so fresh air can enter. Mist the inside walls of the humidity tent as needed. Avoid soaking the developing mushrooms directly. Make sure the air around the block does not feel stale.

What Healthy Growth Looks Like

Pins should begin forming on the top surface of the block. Healthy Black Pearl mushrooms develop thick pale stems with gray to charcoal caps.

Pins may begin about 7–12 days after opening; full fruiting commonly takes about 10–20 days

If the mushrooms develop unusually long stems, check light and fresh-air exchange. If pins dry out or stop growing, humidity may be too low or airflow may be too drying.

When to Harvest

Harvest when the caps are nearly open and flat, but the outer edges are still slightly curled downward. Do not wait for the caps to become fully flat and heavily spore. Earlier harvest gives better texture and shelf life.

Grasp the cluster firmly at the base. Twist and pull the cluster away from the block, or cut it cleanly at the base with a clean knife.
Remove any leftover stem tissue from the top surface.

Second Flush

Black Pearl is best treated as a primarily first-flush variety. A second indoor flush is possible, but it is less reliable and should not be expected from every block.

After harvest:

Remove leftover mushroom tissue.
Keep the block cool and humid.
Maintain steady fresh air.
Watch for new pin formation.

If a second flush does not develop, you may try the optional Cold Shock method.

Cold-Shock Steps

1. Keep the block inside its grow bag so the refrigerator does not dry it out.
Place the block in the refrigerator at about 35–45°F for approximately 24 hours.
Do not freeze the block.
Return the block to its fruiting area.
Resume 50–62°F fruiting conditions, 85–95% humidity, indirect light, and steady fresh air.
Watch for pins over the following days.

King Trumpet Grow Kit

FAQs and Tips

What is the ideal condition for Black Pearl Oyster mushrooms?

Best temperature: 50–62°F
Humidity: 85–95%
Fresh air: Steady fresh-air exchange; avoid stagnant air and direct fan blast
Light: Indirect room light or low grow light
Fruiting style: Top-fruiting
Expected timing: Pins may begin about 7–12 days after opening; full fruiting commonly takes about 10–20 days
Difficulty: Beginner to intermediate

Should I cut the side of the bag?

No. Black Pearl Oysters are top-fruiting mushrooms. Cut the top of the bag and keep the sides intact.

Do Black Pearl Oysters need a cold shock?

Cold shock is optional, and is NOT part of the normal first-fruiting setup.

Consider it only when:

The block is fully colonized.
It has been in fruiting conditions for about 2 weeks without pinning.
Temperature, humidity, and fresh-air exchange are already in the correct range.
The block is not obviously dried out or contaminated.

Why use it? A short temperature drop can act as an environmental cue that helps a mature, stalled block restart pin formation.

Cold-Shock Steps

Keep the block inside its grow bag so the refrigerator does not dry it out.
Place the block in the refrigerator at about 35–45°F for approximately 24 hours.
Do not freeze the block.
Return the block to its fruiting area.
Resume 50–62°F fruiting conditions, 85–95% humidity, indirect light, and steady fresh air.
Watch for pins over the following days.

Cold shock will not correct chronically low humidity, stale air, excessive warmth, or a dried-out block. Fix those conditions first.

No pins after about 2 weeks

Confirm the temperature is cool enough, humidity is high, and air is not stagnant. If those conditions are correct and the block is fully colonized, use the optional cold-shock reset above.

Long stems with smaller caps

Increase fresh-air exchange and make sure the block receives indirect light. Do not point a fan directly at the mushrooms.

Pins dry out or stop growing

Increase humidity and reduce drying airflow.

Mushrooms or block surface look wet or slimy

Reduce misting and increase gentle fresh-air exchange.

Can I get a second flush?

Sometimes, but Black Pearl is primarily a first-flush variety. A second indoor flush is possible but less reliable than with standard oyster mushrooms.