Australian Log-Grown Shiitake Mushrooms

The cultivation of shiitake mushrooms on oak logs (Quercus spp) has been practiced for centuries in China and Japan. In fact, the word Shiitake literally means Oak-Mushroom . The fungus colonises dead timber then fruits in response to moisture. Field based production of Shiitake on logs is now relatively common practice amongst North American forest owners. Inoculated logs are stacked in the forest to rest then repeatedly treated to stimulate fruiting. A single oak log can be produce mushrooms for up to 4 to 5 years.

I was introduced to Shiitake production by a past student, Parsuram Sharma-Luital. Parsu came to Australia from Bhutan to study for his Masters in Horticulture but is now an Australian resident. Parsu has brought with him a wealth of knowledge, skill and enthusiasm. Back in Bhutan he'd worked with farmers growing mushrooms, including Shiitake.

Research undertaken in the northern hemisphere suggests that Oak (Quercus spp) is the most productive and resilient species for log-based mushroom production. Other species that have been successful include Alder (Alnus spp) and Birch (Betula spp). The fungal mycelium spreads under the bark and throughout the sapwood of the logs. Characteristics that appear to be important are the ability of the log to retain moisture, the bark type and its persistence, and the starch content of the sapwood. There are reports of Shiitake being grown on eucalypts in South America but we know of no examples in Australia .

Parsu with oak logs

With many landholders now establishing and managing plantations for sawlog production there is clearly interest in the potential for using eucalypt thinnings. If this can be done cheaply, on-farm, shiitake mushrooms may provide a useful early commercial return for forest owners growing sawlogs. We have been trialling the production of Shiitake on a range of Eucalypt species and comparing their performance with English Oak (Quercus robur).

Log Based Shiitake Mushroom Production - What we have learnt

I'd like to take readers through the production process in greater detail. Those who are interested in taking it further will be frustrated to find that it is currently difficult to obtain the spawn required for log inoculation. We hope to be able to assist by producing spawn locally or importing more material from the USA . You are welcome to contact me by email and I will add your name to my shiitake email list. This way we can keep you informed about future workshops, research results, the manual and sources of inoculant.

Rowan with a Shining Gum (left) and Oak log in full production

The Species: Lentinula edodes

Shiitake is a type of White Rot Basidiomycota (mushroom type) fungi that decomposes cellulose and lignin. The fungus is native to China and widely grown commercially across temperate East Asia ( Japan and Korea ) and more recently in North America . There is some conjecture about whether or not Lentinula edodes is actually indigenous to Australia . The Interactive Catalogue of Australian Fungi published by the Royal Botanic Gardens in Melbourne acknowledges that there is a closely related species ( L. lateritia ) found in Queensland and Tasmania (and PNG) that will hybridise with L. edodes . DNA research suggests the two species share the same ancestral roots and may only differ as a result of thousands of years of human domestication.

The Spawn

The spawn we have been using was produced by Fungi Perfecti, a certified organic producer in Washington State , USA ( www.fungi.com ). We will be working with them to test a number of potential strains that may be suited for use with Eucalypts and more tolerant of our relatively dry conditions.

We receive the spawn on sterilized grooved birch plugs that are fully colonized by pure mushroom mycelium. The 8mm diameter dowels are inserted into a series of holes drilled along the log. Once the wood is fully colonized (typically 9-12 months) mushrooms will spring forth from cracks or channels in the wood. Generally, the best time of year to inoculate logs and stumps is in the Spring due to the higher starch content in the wood.

Members of the Otway Agroforestry Network inoculating their logs

The Spawn Run

It takes a few months for the fungus to spread its mycelium through the logs and the logs will not fruit until they are fully colonised. The fungal mycelium spreads under the bark and throughout the sapwood of the logs. The sapwood is the part of the stem which carries water up to the canopy. During the winter starch and sugars are stored in the sapwood and used to drive rapid leaf growth in early spring. By cutting logs in late winter we are able to capture the starch in the logs and use it for growing mushrooms.

We have watched the way the mycelium spreads and it reflects the way other wood decaying organisims move through trees. Initially the fungus travels freely up and down the length of the logs then slowly around the logs until it fully occupies the sapwood area. None of the mycelium spreads into the heartwood area, even in non-durable wood species. Having occupied the logs the shiitake is able to fend off other wood destroying pathogens resulting in slower than expect decay of the timber.

The Mushrooms

To initiate fruiting the fully colonised logs are soaked for 24 hour in the water. After soaking, logs they must be watered 3-4 times a day. 'Pinning' is the term used to describe the formation of small knots or bulbs that arise on the surface of the bark. At this stage it is important to keep the logs moist as the mushrooms develop. Mushrooms will be ready 2-3 weeks after soaking and should be picked just before the lip of the mushroom turns outwards.

Once the logs have finished fruiting they are rested for few months before the process is repeated. We anticipate that the best logs will remain viable for 4 or 5 years and may produce as much as 1 kilogram of fresh produce per year. The total number of mushrooms you can expect to get will vary from log to log, and from season to season. Any outdoor log-based mushroom cultivation project involves a number of variables; climate, species, sugar and moisture content of wood, consumption of mushrooms or mushroom mycelium by insects and other animals, quality of care and just plain old chance, to name a few.

Ready to pick off an Oak log

Diseases and pests

We have had problems with a small fruit-fly laying eggs in the gills of the mushrooms. These can be controlled using a pyrethrum spray but I prefer to store the fruiting logs under a fine screening material like that available at many garden stores for use over strawberry plants.

Excess watering will encourage Trichoderma and other mould growth on the surface of the logs which will compete with shiitake mycelium. This can be controlled reducing the rate of watering or sheltering the logs from persistent rain (remember that?).

Slugs and snails will eat the mushrooms although these are easy to control by having good drainage. If they persist you may need to use snail baits. Possums will eat the mushrooms directly off the logs and can be a real pest.

The Logs

Shiitake prefers to grow on hardwoods. This does not mean 'hard' wood. The term is a biological one that is used to distinguish the flowering plants (which include all the deciduous and broadleaf species including eucalypts) from the conifers or softwood species like pine or cypress. We have trialled a number of species and have developed our own ideas about what makes a suitable log for shiitake production.

Research undertaken in the northern hemisphere suggests that Oak ( Quercus spp) is the most productive and resilient species. Other species that have been successful include Alder ( Alnus spp) and Birch ( Betula spp). We have trialled the production of Shiitake on English Oak ( Quercus robur ), Shining Gum ( Eucalyptus nitens ), Sugar Gum ( E. cladocaylx ), Poplar ( Populus hybrid spp), Common Alder ( Alnus glutinosa ) and Blackwood ( Acacia melanoxylon ). Although Oak has proved the most productive it is clear that the eucalypts, although slower initially, can be very productive. Blackwood is improving over time. Poplar was too difficult to keep moist and has been discarded.

Eucalytpus nitens logs producing well.

Characteristics of the log that appear to be important are the ability of the log to retain moisture, the bark type and its persistence, and the starch content of the sapwood. Cutting your logs in the late Winter or early Spring helps to insure that they have a high sugar content, although this is not strictly necessary. When preparing logs it is important to make a clean chain-saw cut at each end and ensure that the bark remains tight. If the bark lifts or tears it is unsuitable.

The bark is the most critical factor in the eucalypts. Very thick bark,of the type found on slow growing trees of species like Spotted Gum or Sydney Blue Gum, tends to suppress the mushroom growth and is susceptible to breaking away from the wood if it dries. The stringybarks are likely to 'fall apart' over time. The best option appears to be the thin barked logs cut from fast growing young trees of the gum-bark species.

We prefer to have logs about 1m long and between 10 and 20 cm in diameter. Any smaller and there is a greater risk of drying out. Any larger and the logs are difficult to handle. Physical handling of the logs is the greatest cost and increases the risk of bark damage. We are working with a few growers who are looking to develop more efficient ways of dealing with multiple logs.

Freshly-cut logs should not be inoculated immediately; trees naturally produce anti-fungal compounds, which degrade in two to three weeks from cutting. Using a 5/16 th drill bit drill a series of holes into the log and insert the dowels. The fungi spreads freely up and down the log so it is best to offset the holes around the circumference to aid colonisation. Our research suggests that 25 to 30 dowels per log are sufficient. At a cost of around 15 cents each it is important not to over-inoculate. The mushrooms can arise at any point along the log and yields do not necessarily relate to the number of dowels inserted in the log.

The dowels are hammered into the holes and pushed down below the bark. We've been using beeswax to seal the end and each of the drill holes to slow drying but are told that paraffin wax may be a cheaper alternative.

Log Storage

Once inoculated the logs should be stored off the ground on other logs or pallets for a few months in a shade location. It is important to water 1-2 times a week. The mycelium spreads rapidly up and down the log from each point of inoculation resulting in wedges of infection thoughout the sapwood. The ideal environment is one that is humid and shaded yet well ventilated. The logs do not need to be held in the dark. The idea is to maintain the weight, hence the moisture content, of the logs and prevent them from end-splitting. The logs should not be covered with plastic as this will encourage mould growth.

In North America I visited a number of farms where the owners had stacks of logs in the forest under a dense tree canopy. In Korea the farmers often store their logs in well-shaded pine forests. In both cases they do not experience the many days of low humidity we get every summer. It is important to have some means of wetting the logs regularly. Using a simple timer it is possible to ensure there is a number of watering each day.

For fruiting you need a higher humidity and more regular watering. I have used a solar pump to drive a small irrigation system that sprays the logs whenever the sun is out. This allows the logs to dry out on cloudy days and over night. The water is captured and recycled. I anticipate that our growers will find innovated ways of setting up their facilities as they gain a greater knowledge of what is required.

Marketing:

Both our large supermarket chains are selling shiitake mushrooms grown in controlled environment facilities in New South Wales and Tasmania . They retail for around $5 for a 100g punnet. The wholesale price in Melbourne for loosely packed bulk shiitake mushroom is around $30 per kilo.

If successful, a small stack of say 20 logs will provide enough mushrooms to keep you family and friends well supplied. You could use excess to introduce the mushrooms to others. Having 20 to 50 logs should be sufficient to maintain production for direct marketing to restaurants and shops. A commercial facility might involve more than 500 logs and the sale of produce through wholesale markets. If there are a number of growers with good yields it may be worth exploring collective marketing.

Environmental risks

There is little information available on the environmental risk of introducing Lentinula edodes . AQIS has been fully advised and have approved importation of the material. However, it is clear that the fungus can spread in woody material through direct contact and the mycelium does grow on damp soil. Whilst the need for almost constant watering and protection from insects suggests that it is unlikely to fruit effectively in most environments, it is prudent to adopt a risk minimisation approach.

The fungus can be killed by allowing it to dry out. We recommend growers inoculate the logs in a clean, dry area and that any old logs are left to dry out in full sunlight and then burnt. All mushrooms produced should be harvested. Until we know more, please do not stack or dispose of inoculated logs or mushrooms in a moist gully under or close to native forests particularly if the site is at risk of flooding.

For details contact me on rfr@unimelb.edu.au

Rowan Reid