Interest in growing specialty mushrooms is proliferating, owing to the increasing interest in alternative protein sources and the health benefits of specialty mushrooms.
Shitake Mushroom growing on a log.
Image Credit: G. Shepherd, 2008
Types of Specialty Mushrooms Grown in South Carolina
- Shitake (Lentinus edodes)
- Oyster (Pleurotus ostreatus)
- Reishi (Ganoderma lingzhi)
Understanding Mushroom Growth: Key Steps in the Production Process
- Substrate Selection- Choosing the right growing material
- Inoculation (Spawning)- Introducing the spawn to the growing media
- Spawn Run- Process of fungal mycelial growth to colonize the substrate completely
- Fruiting- Period of mushroom appearance and harvesting
Choosing the Right Substrate for Mushroom Growth
The substrate provides a carbon source for the fungus to utilize for energy. The mushrooms discussed are all saprotrophs, which obtain energy from decomposing plant material. Saprotrophs derive their food (nutrition) from decomposing organic material.
Many different substrates are utilized for mushroom production, ranging from hardwood logs to straw or sawdust blocks.
Stacked logs in an A-Form. Notice the drip line running above the logs to allow for supplemental watering.
Image credit: UGA Extension 2020
Hardwood Logs
One of the most common substrates for specialty mushroom production is hardwood logs. Oak logs are the most used. Avoid any coniferous species, and ash or cherry. The decomposition process required for pine species differs slightly from that of hardwoods, and the process often releases fungal toxic compounds. Cherry and ash, for example, tend to be quickly colonized by the fungi, which results in an earlier yield but will decompose more rapidly, reducing the overall yield of the mushroom.
The chosen log should be four to six inches in diameter and three to four feet long.
The log should also be relatively fresh, with a moisture content of over 29%. Wood below 29% makes for excellent firewood but is unlikely to be conducive to fungal growth. If the option exists, logs can be harvested when the trees are dormant in the late winter to provide a fresh substrate.
Inoculated logs can be stacked in an A form to prevent substrate drying and minimize rain shadow. A typical firewood stack is ineffective in providing airflow, as the aim is to dry the wood for burning. Drying will inhibit fungal growth.
Notice the drip line running above the logs to allow for supplemental watering.
Straw
Straw and other crop residues have a relatively low nutrient content and are more suited to oyster mushrooms than other species. Straw needs to be further treated to aid in effective mushroom cultivation.
The first step is to chop or shred the straw, which helps to separate the fibers of the substrate, allowing for increased surface area and for the mycelium to move through the material. Fungal mycelium is a root-like mass of fine threads called hyphae, which the fungus uses to colonize and spread through the substrate. Without the vegetative hyphae (roots), the fungus cannot extract the nutrients required to form fruiting bodies (the mushrooms themselves).
Once the straw is chopped or shredded, it is necessary to treat it before inoculation.
Cultivation should be done indoors to prevent insects from laying eggs on the substrate and adversely affecting the mushrooms.
Cold Fermentation
Cold fermentation is the easiest method of treating straw and involves soaking the shredded straw for five to ten days. The process requires the straw to be submerged in water. The higher the temperatures, the lower the time. The process is very smelly, but it can be inoculated immediately after draining the straw.
Hot Pasteurization
In this method of straw treatment, the aim is to keep the substrate at 160 °F for 2 hours to reduce pathogen loading. The simplest method is to heat water to 180°F, then allow the material to cool in a covered container for 2 hours.
After the straw has been heat-treated, spread it out on a clean surface and allow it to cool below 100 °F to enable it to be handled and inoculated.
Sawdust Blocks
Blocks are commercially available for purchase. Purchasing blocks is recommended because forming blocks takes a lot of time and space. Block formation also needs to be carried out in an indoor lab environment.
Mushroom Inoculation: Methods and Techniques
Inoculating logs using dowel plugs.
Rob Last ©2025, Clemson Extension
Regardless of the substrate being used, follow the steps below. For a natural log, holes must be drilled deep enough for the spawn to be inserted. The holes must be drilled to a 7/16 inch diameter with holes spaced every six to eight inches.
Each row of holes should be two inches apart and offset to create a diamond pattern.
An inoculant or spawn is pure mycelium and can be purchased as a sawdust mixture or a dowel plug. For the sawdust spawn, fill the predrilled holes with the inoculant and cover them with food-grade wax.
Tap the dowel into the holes and cover the dowel with food-grade wax.
If supplemental water is unavailable, seal the logs’ cut ends with food-grade wax to minimize the potential for the logs to dry out.
If straw is the substrate of choice, the spawn (mycelia) should be thoroughly mixed with the straw and packed into containers. The containers can be a 5-gallon bucket with 5/8 inch holes drilled in a diamond pattern every six to eight inches.
Spawn or Spores? Which is Better for Mushroom Cultivation?
- Fungi disseminate their genetic material using spores; however, handling spores for an accurate inoculation process can be very challenging.
- Sterile mycelia, or spawn, are live strands of fungus, which are easier to handle and thus lead to a greater success rate.
Managing the Spawn Run: Ensuring Optimal Mycelium Growth
Spawn run is the process of fungal mycelial growth to colonize the substrate completely. The process usually occurs in a laying yard, with attention to light, humidity, and temperature. The substrate should be inoculated after the last spring frost. As mentioned, the substrate cannot dry out, so water applications may be necessary to avoid periods of strong sunlight.
The laying yard is where the logs will be stacked to allow for fungal colonization. The site should be shaded with consistent moisture and temperature. If the laying yard is in full sun, shade cloth providing 80% shade can be a practical addition.
Fruiting: How to Encourage Mushroom Growth
Fruiting refers to the period of mushroom appearance and harvesting. Fruiting can occur in as little as 3 months for oyster mushrooms or up to 18 months for shitake mushrooms on hardwood logs.
Indoor vs. Outdoor Mushroom Production: Which is Best?
Fungi are adapted to various environments and can be grown indoors using artificial light or outdoors in a shaded area. There are benefits and drawbacks to each method of production.
Indoor Mushroom Cultivation
Growing specialty mushrooms indoors enables the producer to control the environment completely. Light, moisture, temperatures, and humidity can all be regulated to provide optimal growth conditions, reducing crop development times and allowing for increased and more predictable year-round production.
Sanitation in indoor facilities is critical to prevent pathogens and insects from building up within the facility.
Growing Mushrooms Outdoors
If production occurs outside, the producer needs to regularly monitor the light and moisture of the substrate to ensure successful production. To provide additional shade, an 80% shade cloth can be used, and the use of misters can be beneficial in preventing the substrate from drying out.
Production outdoors will be much more seasonal and may be less predictable than indoor production.
Substrate and Inoculation Materials
| Mushroom | Suitable Substrate | Inoculant Available |
| Oyster | Straw | Plug Spawn Sawdust Spawn Grain Spawn |
| Shitake | Hardwood Log Hardwood Sawdust Blocks |
Plug Spawn Sawdust Spawn Grain Spawn |
| Reishi | Hardwood Log Hardwood Sawdust Blocks |
Plug Spawn Sawdust Spawn Grain Spawn |
References
- Kristen E. Bowers, Stephen D. Hight, Neil W. Miller, Alexander M. Gaffke, Jennifer E. Taylor. “Use of nonnative, invasive tree logs for commercial mushroom production,” Invasive Plant Science and Management, 17(2), 79-85, (20 May 2024)
- Mushroom Production Basics on Natural Logs
- Four Methods of Mushroom Production, Cornell College of Agriculture and Life Sciences.
- Six Steps to Mushroom Farming
- Ma, Yongsheng, Liu, Lingyun, Zhou, Xiaoyan, Tian, Tian, Xu, Shuai, Li, Dan, Li, Cangtian, Li, Yu. “Optimizing Straw-Rotting Cultivation for Sustainable Edible Mushroom Production: Composting Spent Mushroom Substrate with Straw Additions.” Journal of Fungi (Basel), vol. 9, no. 9, 2023, pp. 925-, https://doi.org/10.3390/jof9090925.
