How to grow reishi mushrooms
Ganoderma lucidum
Reishi fruits on hardwood sawdust or logs at 65–80°F (18–27°C), with antlers about 7–12 weeks after spawning and conks in about 4–6 months. CO2 decides which shape you get.
By Derick · October 24, 2026
- Fruiting temperature
- 65–80°F (18–27°C)
- Humidity
- 95–100% RH for antlers, 85–95% for conks
- Spawn to first harvest
- About 7–12 weeks (antlers); 4–6 months (conks)
- Grows on
- Hardwood sawdust with bran, or hardwood logs
Difficulty: Moderate. Reishi antlers grow in a closed bag with almost no care, but conks need months in open air, where the slow block is more exposed to contamination (North Spore booklet).
Reishi growing conditions at a glance
| Stage | Temperature | Humidity | Fresh air / CO2 | Light | Days |
|---|---|---|---|---|---|
| Bulk colonization | About 77°F (25°C) | Sealed bag | None; bag stays closed | Dark | About 20–25 |
| Antler growth (bag closed) | 65–80°F (18–27°C) | 95–100% RH | CO2 20,000–40,000 ppm | Ambient light | About 28–60 |
| Conk growth (bag open) | 65–80°F (18–27°C) | 85–95% RH | CO2 under 2,000 ppm | About 800 lux | About 60–90 |
Where these numbers come from
- Colonization: Oregon State Extension gives blocks about 20 days to colonize (Oregon State Extension). A 2025 lab study colonized bags in the dark at 77°F (25°C) in 25 days (Journal of Fungi). India's ICAR mushroom centre runs warmer, at 28°C (82°F) or more, also in about 25 days (ICAR).
- Temperature, humidity and CO2: North Spore lists 65–80°F, 95–100% for antlers and 85–95% for the fruitbody, and CO2 of 20,000–40,000 ppm for antlers and under 2,000 ppm for conks (North Spore booklet).
- Days: North Spore allows 1–2 months for antlers, plus 2 months for a conk. Oregon State sees antlers in about 28 days, and conks over 75–90 days on blocks planted outdoors.
- Light: North Spore keeps the closed bag in ambient light. ICAR uses 800 lux once the bag is cut open to start pins.
The fruiting temperature, humidity and CO2 ranges rest on North Spore alone, a company that sells spawn and grow kits. The studies above support the direction of the CO2 effect, not North Spore's exact numbers.
What does reishi grow on?
Supplemented hardwood sawdust
Oregon State's blocks are 5 lb of hardwood sawdust and bran, sterilized and spawned with grain. ICAR adds 20% wheat bran and wets the mix to 65% moisture (ICAR).
Hardwood logs
Oregon State uses oak or maple, 2–4 ft long and 4–7 in across, inoculated within 30 days of felling. The spawn run takes nine months or more, and a log fruits for about one year per inch of diameter (Oregon State Extension).
Blocks buried outdoors
Once antlers reach 1–3 in, Oregon State takes blocks out of their bags and plants them under shade, where a conk forms over 75–90 days.
How to grow reishi, step by step
Colonize grain spawn
Grain takes 2–3 weeks and is ready when it's uniformly white (GroCycle). See grain spawn.
Colonize in the dark
Keep the sealed bag dark for about 20–25 days. Colonization is done when the bag is white all over.
Grow antlers in the closed bag
Don't open the bag: reishi needs its humidity and CO2 to form antlers. Put it in ambient light and turn it now and then (North Spore booklet). Antlers are done when they reach the size you want.
Open the bag for conks
For conks, North Spore opens the top of the bag once antlers are over 4 in tall and moves the block into a fruiting chamber at 85–95% and under 2,000 ppm. A conk is done when its white edge has turned red.
Harvest and dry
Twist or cut at the base; reishi is corky and tough (Oregon State Extension). Trim off substrate and dry it in open air or at low heat.
What's different about growing reishi?
CO2 decides antlers or conks
Reishi grows finger-like antlers in high CO2 and a shelf, or conk, in fresh air (Oregon State Extension). The thresholds vary by source:
- North Spore grows antlers at 20,000–40,000 ppm and conks under 2,000 ppm.
- In a 2025 study, reishi at 3,000 ppm grew antler-shaped bodies that couldn't form a normal cap; the control room was at 400 ppm (Journal of Fungi).
- A 1975 study found 1,000 ppm already favored stem growth over the cap, and capless fruit bodies formed a cap once CO2 fell (Lu and Chang).
So the bag is the control: closed for antlers, opened for conks. Our CO2 guide covers measuring it.
Slow by design
Reishi is slower to mature than shiitake, oyster or lion's mane on any substrate (Oregon State Extension). Log spawn runs take nine to 18 months. Plan in months, and expect long stretches where nothing seems to change.
When and how do you harvest reishi?
Pick reishi antlers by twisting them off at the base, then trim the substrate and air-dry them (North Spore booklet). A conk is ready when its margin turns from white to red (Oregon State Extension). ICAR waits until the cap is fully reddish brown and shedding spores, and dries it below 50°C (122°F) (ICAR).
Flush counts vary. North Spore expects one crop from its bagged block. Oregon State gets two flushes a season from logs and planted blocks. ICAR gets 2–3 flushes in about four months, totaling 25% biological efficiency: 250 g of fresh reishi per kg of dry substrate. ICAR notes reishi is bitter and corky hard, so it isn't eaten as a food mushroom.
Common reishi problems
Antlers keep growing but never cap
CO2 is too high for a cap. Open the top of the bag and give it fresh air exchange; a capless fruit body can still form a cap once CO2 drops (Lu and Chang).
Mold after opening the bag
North Spore warns of a greater contamination risk once the bag is open, because reishi grows slowly (North Spore booklet). Check the block daily, and bag up and throw out a block that turns green; see trichoderma and the contamination ID guide.
Spore dust over the block and tent
A mature conk sheds spores; ICAR treats that as the sign of full maturity. North Spore says one mushroom can release billions of spores a day, and harvesting on time protects your fans and filters (North Spore booklet).
Nothing seems to happen for weeks
Usually normal. North Spore allows 1–2 months for antlers alone. Check that the bag is fully colonized and still sealed before changing anything.
Tracking a reishi grow in Hypha
Hypha logs each reishi block from inoculation to harvest. Its reminders start from typical timings, so push a reishi block's fruiting and harvest dates out to fit a run measured in months. Photos are organized by grow, with side-by-side comparisons, so you can watch antlers form and see when a conk's edge turns red. Harvests are recorded by flush.
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Reishi growing FAQ
How long does reishi take to grow?
Reishi antlers are ready about 7–12 weeks after spawning a bag: about 20–25 days to colonize, then 1–2 months of antler growth. A conk takes about two months more (North Spore booklet). Logs take nine months or more just to colonize (Oregon State Extension).
Can you grow reishi indoors?
Yes. Reishi antlers grow indoors in a closed bag in ordinary room light, with no fruiting chamber. Conks need a humid Martha tent or chamber once the bag is open.
What temperature does reishi need?
Reishi fruits at 65–80°F (18–27°C) by North Spore's range, warmer than lion's mane at 55–70°F.
What is the difference between reishi antlers and conks?
Reishi antlers and conks are the same mushroom grown in different air. High CO2 in a closed bag gives branching antlers; fresh air lets it form a flat, shelf-like cap.
Is reishi hard to grow?
Reishi isn't hard, and North Spore rates its block for beginners. It is slow, and an open block sits exposed to contamination for months.
Sources
- North Spore booklet (cdn.shopify.com/s/files/1/2418/8179/files/FruitingBlockBooklet…)
- Oregon State Extension (extension.oregonstate.edu/pub/em-9364)
- Journal of Fungi (pmc.ncbi.nlm.nih.gov/articles/PMC12842923)
- ICAR (dmrsolan.res.in/Folder_Ganoderma.pdf)
- GroCycle (grocycle.com/how-to-make-grain-spawn)
- GroCycle (grocycle.com/growing-lions-mane)
- Lu and Chang (jipb.net/EN/abstract/abstract24788.shtml)
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