Shiitake popcorning: what the bumpy stage means
Popcorning is the bumpy, lumpy stage on a shiitake block before pins form. It is described as a normal stage. Follow your seller's steps for browning, chilling and soaking, and contact the seller if the block looks wrong.
What popcorning is
Popcorning is a stage on sawdust blocks of shiitake, before pins form, when the surface grows bumpy, nodular lumps. One food-forest writer describes it as bumpy, nodular "popcorn" structures that appear before pinning, especially on sawdust blocks.
North Spore's own FAQ does not cover popcorning. One customer review on North Spore's shiitake page mentions popcorning and pinning while waiting for the block to brown, and says support told them that was fine. That is one customer's account, not the seller's guidance, so contact your seller if the block looks wrong to you.
What North Spore says to do with a shiitake block
Shiitake is the odd one among common kits, because the block does not stay in its bag. These are the steps from North Spore's shiitake pages and booklet:
- Let the block brown in its bag. The booklet says this takes about 1 to 2 months.
- Refrigerate the block for at least 48 hours.
- Soak it for about 4 hours.
- Do not put it back in the bag.
North Spore's booklet says that once a shiitake block is in a fruiting chamber, fruiting takes about 1.5 to 2 weeks, and it lists 2 to 4 crops. Field & Forest says yield declines with each fruiting and to expect typically 1 to 3 fruitings. Both are seller claims.
Harvest and green mold
North Spore says to harvest shiitake just before the caps flatten and to trim the stems flush with the block. Grocycle describes the sign as edges curled under with about 80% of the gills exposed. Field & Forest says to store harvested mushrooms in the refrigerator.
If you see green mold, North Spore suggests spraying the affected areas with 3% hydrogen peroxide, while Field & Forest suggests bleach in the soak water. Follow your own seller's sheet. See mycelium vs mold for the colors to watch for, and the shiitake mushroom grow kits page to compare kits.
For the general method, see how to grow mushrooms at home.
Keep reading
- Mushroom grow kit troubleshooting: bumpy, dry or stalled kits
- Mycelium vs mold on a grow kit: what is normal and what is a problem
- Harvest timeline tracker: dates for the browning, chilling and fruiting stages
Back to How to grow mushrooms at home
Common questions
Is popcorning on a shiitake block normal?
It is described as a stage before pinning on sawdust blocks, with bumpy lumps forming on the surface. North Spore's FAQ does not cover it, so contact your seller with a photo if the block looks wrong to you.
Should I take a shiitake block out of the bag?
Yes, but only after it has browned and been chilled. North Spore says to refrigerate the block for at least 48 hours, soak it for about 4 hours, and not put it back in the bag.
How many harvests does a shiitake block give?
North Spore's booklet lists 2 to 4 crops for shiitake, and Field & Forest says 1 to 3 fruitings, with yield declining each time. Both are seller claims.
What if I see green on my shiitake block?
North Spore suggests spraying affected areas with 3% hydrogen peroxide. Field & Forest suggests 2 capfuls of bleach per gallon of soak water. Follow the sheet that came with your block.
Sources
- Organic Shiitake Mushroom Grow Kit Fruiting Block, North Spore. Checked November 11, 2026.
- Fruiting Block Kit Instruction Booklet (PDF), North Spore. Checked November 11, 2026.
- 3 pc. Organic Shiitake Fruiting Block Kit Bundle, North Spore. Checked November 11, 2026.
- Shiitake Ready-To-Fruit Blocks, instruction sheet, Field & Forest. Checked November 11, 2026.
- The Beginner's Guide to Harvesting Mushrooms, Grocycle. Checked November 11, 2026.
- Shiitake Mushrooms (Lentinula edodes), Gavin Mounsey. Checked November 11, 2026.
How this page is checked
Cedrick Reese wrote this page from North Spore's shiitake pages and booklet, Field & Forest's instruction sheet, Grocycle's harvest guide and one food-forest author's description of popcorning. No seller FAQ defines popcorning, so the definition rests on that one outside source and is labeled as such. We have not grown shiitake for this page, and the timings are the sellers' numbers.