How to Grow Shiitake Mushrooms with a Grow Kit

Enjoy rich, umami-packed shiitake mushrooms grown right at home with this easy-to-use Ready-to-Fruit Kit from Redwood Mushroom Supply. Each block arrives fully colonized and prepared to produce dense, flavorful mushrooms—no special lighting, lab work, or prior experience required.

Shiitake fruiting works differently than oyster mushrooms and Lion’s Mane. Shiitake blocks often arrive brown, bumpy, or covered with white “popcorn-like” growth. You may even see small mushrooms already forming inside the bag. This is normal and usually means the block is mature and ready to fruit.

Unlike oyster blocks, shiitake should not be fruited by cutting a small slit in the original plastic bag. For best results, remove the plastic completely and give the block high humidity with gentle fresh air.

How to get started

Remove the Plastic Grow Bag

Carefully cut away and remove the original plastic grow bag completely. Shiitake should fruit as a bare block, not through a slit in the bag.

Place the bare block upright on a clean plate, tray, or shallow dish.

If small mushrooms are already growing inside the bag, this is normal for a mature shiitake block. Remove any mushrooms that look overgrown, damaged, slimy, or trapped against the plastic. Healthy-looking mushrooms can be harvested.

Control the Humidity

A. Growing in an Automated Mushroom Tent

If you are growing inside an automated mushroom grow tent with a humidifier and fan, place the bare block on a clean tray or rack.

Maintain high humidity, ideally 85–95%, with gentle fresh air. Avoid direct fan blast and avoid heavy direct misting on pins or mushrooms. Do not cut slits in the grow bag and do not leave the block sealed in plastic. Shiitake should fruit as a bare block.

B. Growing on the Countertop: Create a Humidity Tent

If you are growing on a countertop, loosely place a clean plastic bag over the shiitake block to create a simple humidity tent. The bag should be large enough that it does not press tightly against the block or mushrooms.

Fill the included sprayer with filtered or distilled water and mist the inside walls of the plastic humidity tent 1–2 times per day. The goal is to keep the air around the block humid, not to soak the block directly.

Leave the bottom of the bag loose or cut several small holes so fresh air can enter. If the inside of the bag looks overly wet or stale, briefly lift it once or twice per day to refresh the air. Keep up this routine, and you will begin to see large lumps forming on the surface where mushrooms will appear.

Watch for Healthy Growth

Shiitake mushrooms can take longer to develop than faster-growing mushrooms like lion's mane and oysters. You may already see popcorn-like bumps, small pins, or premature mushrooms when the kit arrives.

Normal shiitake growth may look brown, bumpy, lumpy, or uneven. This does not mean the block is low quality. Browning and popcorning are part of the shiitake fruiting process.

Keep the block in indirect light with high humidity and gentle fresh air. Avoid direct sun, heaters, vents, or strong fan blast.

Harvest Your Mushrooms

A shiitake mushroom is ready to harvest when the cap looks like a wide umbrella that hasn’t fully opened. Imagine it like a beach umbrella that’s just beginning to stretch out—the edges of the cap should still curve downward slightly, not lay flat like a dinner plate. If the cap opens all the way and flattens out, it’s past peak—still usable, but the texture and shelf life won’t be as good.

After harvest, let the block rest before trying for another flush. For a second flush, let the bare block rest for 7–14 days, soak it in cold water for 4–6 hours, drain well, then return it to your countertop humidity tent or automated grow tent. Second flushes are usually smaller than the first.

Second Flush - Cold Soak

After your first harvest, your shiitake block may produce another flush.

Remove leftover stems and mushroom tissue from the block.
Let the block rest for 7–14 days in a cool, clean area.
If the block feels light or dry, soak the bare block in cold water for 4–6 hours.
Drain well.
Return the block to your countertop humidity tent or automated grow tent.
New pins may form within 7–14 days, depending on block condition and environment.

Second flushes are usually smaller than the first flush.

Shiitake Mushroom Grow Kit

FAQs and Tips

What is the ideal condition for Shiitake mushrooms?

Best temperature: 60-70°F
Humidity: High; 85-95% is ideal in a grow tent
Fresh air: Gentle, steady fresh air
Opening style: Remove block completely from the original plastic grow bag
Expected timing: Pins may already be present. New mushrooms often develop within 1-2 weeks.

Why is my shiitake block brown, bumpy, or covered with popcorn-like growth?

This is normal for shiitake. Shiitake blocks go through a browning and popcorning stage before producing mushrooms. White popcorn-like bumps, brown surface texture, and uneven growth are usually signs that the block is mature and ready to fruit.

There are mushrooms already growing inside the bag. Is that bad?

Not necessarily. Premature mushrooms are common on mature shiitake blocks. Remove mushrooms that look overgrown, damaged, slimy, or trapped against the plastic. Healthy-looking mushrooms can be harvested. Then remove the plastic and begin fruiting the block.

How long does it take for Shiitake mushrooms to grow?

Shiitake mushrooms can vary by block maturity and growing conditions. Some mature blocks may already have pins or small mushrooms when they arrive. New mushrooms often develop within 2–3 weeks after fruiting conditions begin. Keep the block humid, provide gentle fresh air, and avoid direct sun or heavy direct misting.
Ideal conditions are 60–70°F (16–21°C) with high humidity (85–95%).

Why are my shiitake mushrooms not forming or growing slowly?

Slow or uneven growth is usually related to humidity, airflow, temperature, or block maturity. Increase humidity around the block by misting the inside walls of the humidity tent. Shiitake prefers steady moisture on the surface and consistent fresh air exchange, ensure air circulation is gentle — not stagnant, but not drafty

Avoid soaking the block directly or spraying young pins heavily. If no mushrooms form after 1–2 weeks, let the block rest, then cold soak the bare block for 4–6 hours, drain well, and make sure the block has had enough resting time after soaking (usually 2–3 days) before expecting pins to appear.

In drier climates, you may need to use a larger bag with holes poked in it, or another fruiting chamber to create the ideal climate.

Can I get more than one harvest from my shiitake kit?

Yes — shiitake kits can produce 2-3 flushes with proper care. After harvesting, let the block rest for 7-14 days, soak it in cold water for 4–6 hours, drain well, then return it to your countertop humidity tent or automated grow tent.

Each flush may yield fewer mushrooms, but the quality remains excellent. Keep your block in a humid environment between flushes to prevent drying out.