Mushroom Production Basics on Natural Logs

These next sections will provide you with several resources to help you learn how to grow shiitake mushrooms using the traditional log production methods developed in Japan over a hundred years ago. The same or similar approach can be used for growing oyster mushrooms. The resources provided below include:

1. a brief narrative description
2. a video of mushroom expert John Boyle demonstrating and explaining the production process
3. a list of sources of mushroom spawn and supplies
4. a list of book, pamphlets and website that provide detailed instructions

The information that follows is intended to give you a general introduction to the three main stages of shiitake production, but this is not intended to be a substitute for reading one or more of the excellent books that describe the in detail the factors and variables that can make the difference between success and failure. The video of John Boyle is intended to allow you to look in on an expert conducting a shiitake mushroom workshop to a group of beginners, but the video only covers the inoculation stage of a 3 stage process that includes inoculation, spawn run, and fruiting. We strongly recommend consulting one or more of the excellent books or pamphlets listed in the Additional Web Resourcessection.

Using Logs

Shiitake mushrooms are grown on hardwood logs, usually 4 to 6 inches in diameter, and 3 to 4 feet long. Many hardwood tree species can be used but oaks are considered best, if available. Cherry and ash should be avoided, as should all conifers. Logs must be relatively fresh, cut from live trees and used within several weeks to no more than several months of cutting. The best time to cut logs is while trees are dormant, either late fall or early spring. Since inoculation should be performed only when the temperature is well above freezing, logs cut early in the winter must be protected from excessive drying by shading and/or covering prior to inoculation in the spring. Maintaining relatively high moisture content is one of the most important considerations and many of the specific recommendations given below are based on maximizing log moisture content. Wood that has been allowed to dry below about 29% moisture is well on its way to becoming well seasoned firewood but it won’t grow mushrooms. Another reason to avoid older logs is because other fungi may have already colonized them, so that the shiitake fungus simply can’t compete.

Stacking

There are many different configurations for stacking logs which varies depending on available space and optimal environmental conditions for the logs. “Dead stacking” like firewood, is not recommended since logs need aeration. Crib stacking [picture] is the most efficient use of space but can result in excessive drying of logs at the top of the stack. Stacking in an leaning A-frame [picture] or Lean-to configuration keeps logs adequately aerated, but drying is reduced compared to cribbing since they are lower to the ground, where humidity is higher during the summer and where snow cover can protect logs from drying during winter

The Inoculation Process

The process of inoculation refers to, introducing into the log a pure culture of the vegetative mycellum of the shiitake fungus. This inoculum, which is also called spawn, is produced under laboratory conditions and is best left to the specialist. There are many commercial sources of high quality spawn, and several of these are listed in the Supplies section. Spawn may be purchased from a commercial suppliers in any one of several formuations but sawdust spawn and plug spawn (short hardwood dowels) are most common for log inoculation.

How it Works

• First, drill holes into the substrate log, using a 7/16” drill bit (for plugs) and slightly larger for sawdust spawn to a depth of **. Holes should be spaced about 4 to 6 inches apart within rows and rows should be 2 inches apart. The holes in adjacent rows should be offset to create a diamond pattern.
• Next, sawdust or grain spawn is inserted into each hole. Sawdust spawn is inserted into the holes using a special tool that “injects”. Plug spawn simply involves tapping the short wooden dowel into the hole with a hammer followed. by waxing.
• Finally, after inoculating, each hole is painted over with hot, liquefied, food grade wax. Waxing the ends of the logs by painting with hot wax or dipping the end into a pot of wax is a practiced that is recommend by some, but not experienced growers. Our advice is to wax the ends of the logs if you do not intend to irrigate (sprinkle) your logs during the spawn run period (defined below) to prevent moisture loss from the ends. If on the other hand you do intend to irrigate regularly leave the ends unwaxed so that water can penetrate from the outside in through the ends of the log.

Definitions

Spawn Run

Spawn run is the period of time necessary for the fugal mycelium to completely colonize the inoculated logs. This occurs in a “laying yard”. As mentioned above, the most important consideration during this period is to prevent the logs from drying out. First and foremost this means to keep them out of direct sun. The shade provided by a dense, closed canopy of trees is ideal. If your forest or woodlot is more open than this you may consider hanging an artificial ceiling of greenhouse woven shade cloth (80% or higher light exclusion).

Fruiting

Fruiting refers to the period of actual mushroom formation and harvest, after the fungal mycellim has fully colonized the substrate log. This may occur in as little as 6 or as long as 18 months for shiitake on hardwood logs, or within as little 3 to 4 months for oyster mushrooms on poplar logs. Forced fruiting of shiitake logs can be achieved by soaking them in cool water for 24 to 48 hours. This allows for more control in scheduling harvests throughout the growing season.

One advantage of shiitake over oyster and other specialty forest mushrooms is that temperature sensitive strains of the fungus are available. These strains fruit at different temperatures so that fruiting can be spread out across the entire growing season. There are cool weather strains, warm weather strains and wide range of other strains.