Tuesday, March 20, 2018

Red Maple: Can this native new weed of the temperate forest make for good mushroom wood?

by Lindsey Bender

Red Maple mid-season
Red Maple is a very successful native tree that appears to be on the move, increasing its predominance across the Great Lakes states and Northeast. Also known as swamp, water or soft maple, it is tolerant to both very wet and very dry sites and everything in-between. Whether the reason for the invasive quality is from decreases in fire frequency, current forestry practices or climate change, there is a worry that Red Maple is replacing regeneration of high value oaks, chestnut and sugar maple. For the mushroom grower, red maple has some great qualities. Stumps sprout in profusion, often growing straight with multiple stems and is very plentiful. It serves as a substrate for Shiitake mushrooms, but its profitability to mushroom growers has been variable at best. At F&FP we have always believed that if we can make it grow a little it can be tweaked to make it grow better. In 2015 Field & Forest Products (FFP) and Misty Dawn Farms (MDF) teamed up on a two-year research project investigating the use of Red Maple for Shiitake mushroom production. 

The short answer is Red Maple is a useful mushroom wood species if you cut in spring during sap flow, use larger diameters (5” in diameter and coarse bark) and let it age 4 weeks prior to inoculation. For more information about the study, see below.

1) Does the month in which the logs are cut make a difference on log success?

Normally we say that logs should ideally be cut during the dormant season (from approximately 1/3 leaf color change in the fall, anytime through winter up until bud swell in the spring). Logs cut during this time typically hold onto their bark longer and are less prone to contamination by other competing fungi. To test whether this is the case with Red Maple, we inoculated over 20 logs every month in a one year period with the “Night Velvet” shiitake mushroom strain and incubated them indoors at 60-70° F with 85-90% relative humidity. Mushroom production was stimulated by force fruiting logs (soaking logs in cold water for 24hrs) after 11 months incubation time, and then mushroom yield was taken for each log. We found that March logs cut during sap flow produced the highest mushroom yields and were the most successful compared to logs cut in all other months of the year. Off all the logs that fruited, larger diameter logs with thicker, coarser bark were more successful than smaller logs with smooth bark.

You can cut Red Maple when the buds are anywhere between these two stages

2) Does the amount of time between cutting Red Maple logs and inoculating influence log success? 

Typically shiitake logs are cut then allowed to sit for a minimum of two weeks prior to inoculation. 
This time allows for cellular dieback in the log and subsequent dampening of the log’s defense system against fungal invasion. Shiitake is a saprophytic fungus that invades and consumes only dead organic matter. The weedy nature of Red Maple means these logs are more prone to re-sprouting (Figure 1). This livelihood means that the log is still capable of fighting against fungal colonization and really reduces mushroom log success. To test this, we inoculated logs either 2 weeks or 4 months after cutting. We found that many of our logs inoculated after only 2 weeks rest period struggled with successful spawn run. Logs that rested four months prior to inoculating were far more successful and productive. This indicates that more than two weeks resting before inoculation is necessary.

Figure 1. The central log has re-sprouted indicating the log is still alive and capable of fighting off shiitake invasion (shown by the lack of spawn run and mycelium on the end of the log).  

3) Is Red Maple a viable wood type for commercial shiitake production?

Many of the red maple logs inoculated only two weeks after felling were only moderately successful. Logs cut and inoculated four months later were far more productive yielding up to 2.3lbs shiitake/log. Unfortunately, disease presence was considerably higher in the Red Maple logs compared to other wood species used for shiitake cultivation (Red Oak, White Oak, Sugar Maple, Aspen) managed similarly.

Results from the red maple logs were compared to standard shiitake logs inoculated and managed under the same conditions. Average yields per log from other wood types during for the first fruiting year include Sugar Maple (0.68lbs/log), Red Oak (0.96lbs/log), White Oak (1.01lbs/log), Aspen (0.89lbs/log), and are comparable to Red Maple cut in December (0.80lbs/log) and Red Maple cut in February (1.02lbs/log) (Figure 2).   

Figure 2. Results from the ideal larger-sized red maple logs were compared to standard shiitake logs inoculated and managed under the same conditions. NOTE: These results are from the first year of fruiting only and do not necessarily represent the overall capability of each wood type over the life of the logs.  Red maple and similar softer hardwood species tend to have shorter fruiting lives than oak logs which remain the recommended log type for shiitake cultivation.  


By selecting for log parameters (coarse bark, >5.5”/14cm diameter), allowing sufficient rest time between felling and inoculation, and controlling for competing fungal disease, red maple logs are capable of producing yields comparable to other wood species commonly used in commercial cultivation of shiitake such as Sugar Maple and Oak species.

There are abundant advantages to being able to utilize Red Maple over standard wood species including cost per log ($2.00 versus $3.00, respectively), increased availability and abundance of Red Maple, increased speed of stand regeneration after wood harvest, faster spawn run in a softer harder, and public willingness to harvest weedy wood species.

Disadvantages – the weedy nature of Red Maple means these logs are more prone to re-sprouting (Figure 1). This livelihood means that the log is still capable of fighting against fungal colonization. To reduce these chances, we recommend letting the logs rest at least 4 weeks (optimal time still being determined) from cutting until inoculation. Secondly, because Red Maple is a softer hard wood, the average life of the log is shorter than hardwoods typically used for shiitake cultivation. Lastly, softer hardwoods like Red Maple are more prone to contamination by competing fungi. Altering log management to reduce these risks may be necessary.

We at Field and Forest Products are constantly striving to improve and clarify the standards for shiitake cultivation to improve success. To do so, we are working on a follow-up to this study examining timing of cut and optimal length of rest time to increase productivity comparing Sugar Maple and Red Maple. We also believe this data will be transferable to other invasive soft maple species such as Norway Maple (Acer platanoides). We will share those results with you in the future!

This two-year research project was funded by the North Central Region of Sustainable Agriculture Research & Education (SARE) program. You can read the full report here on their website:


  1. Great Study! I'm looking forward to the next round of tests now that you've narrowed the hypotheses a bit. Thanks for publishing.

  2. Thats for doing this and getting it out, very useful to those of us with the red maple resource and questions about whether to use it! There are some switches between Months/weeks when you discuss how long to wait for inoculation. I think this may be a typo and just want you to have to opportunity to fix it! Thanks again.

    1. Thank you for your interest! In this study, we found that logs cut four months prior to inoculation were more successful than logs cut just prior (2 weeks). We hypothesized that two weeks was not sufficient time because the logs were still active and capable of fighting off shiitake colonization - impeding spawn run success. While resting logs longer from cut to inoculation would reduce this risk, logs are prone to drying out and contamination with extended resting periods. The logs rested for four months in this study were stored outdoors in a Wisconsin winter and were managed to reduce the risks from long term resting, but we would not, however, recommend storing red maple logs for extended periods of time especially through the warmer months. For these reasons we concluded a rest time of four weeks is ideal.

      We are continuing to investigate cut and rest times for red maple logs and will share our results as they come!

    2. I am still amazed that you can't just cut and inoculate. Is this to say that trees have an immune system?

  3. Any reasearch on the Autumn Blaze Maple which is said to by a hybrid of the Red and Silver Maple?

  4. I can't tell you how happy I am to see you presenting real data! This enables a person to make a really informed decision, e.g., will I substitute aspen for oak or whether or not to use a tree felled in June. So much information one finds comes as "do this, do that" directions that are not easy to customize for the situation at hand. Seeing the difference between aspen and white oak for instance screams at me to get on with that thinning of aspen trees.
    I sure hope some readers will help to reproduce the data (very important, and never to expect perfect agreement), and to fill in some detail, such as weekly intervals post-felling to optimally inoculate logs.
    Side notes: Norway maple is invasive and has kind of ruined autumn colors in much of Pennsylvania - Norway maple just goes yellow in fall. If Norway maple does work as well as red, that's a great argument to cut them down, replace them with red maple or better. And cutting down aspen helps to regenerate shoots that grouse depend on.

    1. Just one point of information here - the error bars on the graph Fig 2. These are standard deviation or standard error of the mean or range? One could say that there is no statistically significant difference among any of the groups.

    2. Hi John, The error bars are standard deviation, and you are right - there is a lot of variation between logs so statistical significance at this point is not measurable between the comparison of wood types. Furthermore, Oak logs and other harder hard woods typically have longer spawn run times than the softer hardwoods, so this graph is probably skewed to favor higher yields in those softer hardwood logs that were capable of fruiting earlier in this first year of data and not necessarily a representation of what the logs will be capable of producing over the life of the log.

      In our continuation study, we aimed to reduce some of the natural variability in the logs (diameter, bark thickness, etc.) to improve our statistical capabilities. We will be happy to share our results as they come in!

  5. any particular reason the strain native harvest wasn't also used in the study?

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