Shiitake do not need logs: Cornell says supplemented sawdust is what most specialty mushroom growers use as a fruiting substrate. That makes blocks the indoor route, and the timeline is far shorter than the 6 to 18 months logs need. Our sources, however, describe commercial block production and not retail kits, so this page is deliberately short and says where the evidence stops. For the main method, see our shiitake growing guide and the on-logs guide.
What a sawdust block is
A block is a bag of supplemented sawdust or wood pellets that has been colonized by shiitake mycelium. University of Illinois Extension describes the commercial version as grow bags with built-in micron filters that allow oxygen and carbon dioxide exchange, with the substrate pasteurized at high temperatures, typically under pressure, for several hours. We found no sourced description of a retail shiitake kit, so check what your supplier sends. Our grow kits guide covers kits in general.
Blocks compared with logs
| Hardwood logs | Sawdust blocks | |
|---|---|---|
| Substrate | Fresh-cut hardwood | Supplemented sawdust or wood pellets |
| Where | Outdoors, in a laying yard | Indoors |
| Incubation | 6–18 months | 4–5 weeks after full colonization |
| Lifespan | 3–4 years of flushes | Not stated in our sources |
The log figures come from Cornell. The block column is limited to what Cornell and Illinois say, and it is not a complete picture, because the time to reach full colonization is not given in our sources.
Incubation and the 55°F problem
Cornell describes the stage after full colonization: shiitakes get another four to five weeks of incubation, during which the block goes through “popcorning” and browning. Temperature matters here. If temperatures drop below 55°F after week 4 or 5, the blocks tend to fruit instead of completing popcorning and browning, and yields fall greatly. Keep the room above 55°F and do not store blocks somewhere cool during this stage.
| Stage | Days | Temperature | Notes |
|---|---|---|---|
| Incubation after full colonization | 28–35 days | Stay above 55°F | Cornell: 4–5 weeks of further incubation. Below 55°F after week 4 or 5, blocks fruit early and yields drop. |
| Logs, for comparison | Not stated | Not stated | 6–18 months to incubate (Cornell). |
Fruiting and harvest
Our sources do not describe how to fruit a sawdust block, how much humidity it needs or how many flushes it gives. What they do give is how shiitake behave once they fruit, and the harvest cues are shared with logs. Maryland Extension says to harvest when the caps are about two-thirds open, and that mushrooms may be stored in a cardboard box for up to a month at 36–41°F. Strain matters for temperature: Cornell groups strains into Wide Range, Warm Weather and Cold-Weather types. Our shiitake harvesting guide has the details.
Contamination
Competing fungi reduce shiitake flush size on logs, according to Cornell. Our contamination guide explains how to spot it. Oyster guidance from UF/IFAS puts blue, green, black or yellow spots as the warning signs on a colonized bag, and our oyster kit guide covers that for a different species.
What our sources do not tell you
We found nothing on retail shiitake kits: price, shelf life, how to open one, the humidity to fruit it or the number of flushes. We also found no time from inoculation to full colonization. If you want a firm timetable, ask your supplier. If you want a source-backed method today, the log route in our on-logs guide is the one our extension sources document in full.
Frequently asked questions
Can you grow shiitake without logs?
Yes. Cornell says supplemented sawdust or wood pellets is what most specialty mushroom growers use for a fruiting substrate. That describes commercial practice.
How long does a sawdust block take compared to a log?
Cornell gives logs 6 to 18 months to incubate. For sawdust blocks, it says that once full colonization is reached, shiitakes have another 4 to 5 weeks of incubation. Our sources do not give the full time to full colonization.
What temperature should sawdust blocks avoid?
Cornell says that if temperatures drop below 55°F after week 4 or 5, blocks tend to fruit instead of completing popcorning and browning, greatly reducing yields.
Do I need to do anything special before fruiting?
Our sources do not give a fruiting procedure for sawdust blocks, so follow the instructions from your supplier.
Sources
- Seven Stages of Cultivation, Cornell Small Farms
- Shiitake Mushroom Basics, Cornell Small Farms
- Block Farming, University of Illinois Extension