Developing Optimal Shiitake Mushroom Production in a Solar Greenhouse Utilizing Spent Shittake Logs as a Sustainable Heat Source

Final Report for FNC03-488

Project Type: Farmer/Rancher
Funds awarded in 2003: $5,950.00
Projected End Date: 12/31/2005
Matching Non-Federal Funds: $19,500.00
Region: North Central
State: Missouri
Project Coordinator:
Nicola Hellmuth
Ozark Forest Mushrooms, LLC
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Project Information


Ozark Forest Mushrooms is a family-owned farm located in the Missouri Ozarks that has specialized in the cultivation of oak-log-grown shiitake over the last 14 years. This farm mushroom enterprise has been an integral part of the farm's forestry management program as monitored by the Missouri Department of Conservation, which promotes a sustainable harvest of oak logs. Ozark Forest Mushrooms has been certified organic for over ten years and promotes a regional forest food to local restaurants and stores in the St. Louis region. Ozark Forest Mushrooms has an established outdoor shiitake fruiting rotation which supplies mushrooms only from May through to the end of October.

The purpose of this project was to extend the growing season and provide year-round production of the shiitakes by using old spent shiitake logs as a fuel source to heat an in-ground greenhouse.

Project Goals:
1. Extend shiitake mushroom growing season.
2. Heating and management of an oak log production system in the greenhouse during the winter and possible use during the summer.
3. Log handling and stacking systems in the greenhouse.
4. Use of shiitake strains year round in the greenhouse.

1. Greenhouse Installation Design
Installation of the original planned in-ground 96 foot x 36 foot greenhouse was adjusted due to problems with the initial excavation of the site due to bedrock. The greenhouse was eventually situated at a higher elevation, but remained adjacent to the shiitake shade house and close to our outdoor production site. The site was also close to an existing well and an electrical pole. The greenhouse was built six feet into the ground with a wooden ledger installed to provide places to attach mobile fruiting racks. A split radiant floor slab was installed (two manifolds were installed so that the floor could be heated at different rates if needed) with a trench drain centered down the middle of the greenhouse slab. Drainage was of paramount importance in the design due to the emptying of 300 gallon water tanks, overhead irrigation and misting.

Greenhouse hoops were then attached to the concrete wall using inserts and a double wall plastic roof was installed. The two layers are separated by means of an electric air pump. Roll up walls were installed so that the greenhouse can be ventilated manually. The greenhouse was purchased as a kit from FarmTek and also included a propane gas furnace, ventilation fans and vents which were also installed so that the greenhouse had a source of emergency back-up heat. An electrical panel, water hydrant and metal drain plates were installed so that the drain can be easily cleaned.

The greenhouse outside walls were insulated with panels and then in filled with gravel for drainage and then clay soil. The purpose of the greenhouse being in ground was to insulate the area from fluctuating temperatures. The concrete walls provide an area to attach fruiting racks and lean shiitake logs against. The inserted wooden ledger also provided places to install hooks for the mobile fruiting racks. A cement wall and floor also can be swept, hosed and, if needed, sterilized and kept free of debris where pest and weed problems can occur in a controlled environment.

2. Furnace Installation and Radiant Floor Management
A Heatmor 400DCSS furnace was installed (400,000 BTU) which can heat up to 10,000 square feet and holds 155 gallons of radiant floor fluid. The 54-inch-deep firebox can easily hold and burn 48-inch spent shiitake logs. The furnace was installed 25 feet away from the greenhouse and an area set aside for stacking spent logs during the winter months. The thermostat in the greenhouse was kept at 70 degrees F. Ash is removed from the fire box by rotating an auger and can be collected for use on a nearby vegetable garden.

Maintenance of the furnace is minimal and requires a weekly check on fluid levels in the radiant floor tubing and occasionally a top up with food grade antifreeze during the winter months. Loading the firebox during the coldest part of the winter did require four to five firebox loads of wood. The spent logs burnt so readily that for overnight burning, larger greener logs were used to supplement the spent shiitake logs during the coldest periods. Temperatures were maintained above freezing in the greenhouse, 40 degrees F minimum up to highs during the day of 60 to 70 degrees F, depending on the amount of sunshine. An exhaust fan was programmed to vent the greenhouse when temperatures reached 80 degrees F during sunny winter days.

3. Shiitake Log Management and Production in the Greenhouse
Winter Production: 70 percent shade cloth was installed inside the greenhouse during the winter months so that with the added 10 percent shade affect of the double wall plastic, it would simulate an 80 percent shade as we have in our outdoor production. Use of grommets, a tall ladder and twist ties made installing the shade cloth a simple task. Three pieces of shade cloth were purchased so that they could hang between the ventilation fans.

Summer Production: In April, the shade cloth was moved and placed on the outside of the greenhouse for the summer months, side panels were rolled up so that the greenhouse structure could be used for fruiting even in the height of one of the hottest summers on record with many days with outside temperatures over 100 degrees F. After investing so much on such a structure, it was important that the structure was useable year round on the farm for mushroom production as well as some seedling propagation for vegetable garden.

The first use of the greenhouse started in the fall of 2004 when newly inoculated logs from the spring of 2004 were moved into the greenhouse from our outdoor shadehouse area. Some logs were soaked in our outside tanks for 24 hours and then moved straight into the greenhouse. Logs were stacked in different ways and the farm manager came up with a simple welded “sucker rid” rack frame which allowed logs to be stacked in a lean-to fashion which also made the most efficient use of space and ease for picking. After each rack fruited, the logs were stacked in a crib stack fashion on the other side of the greenhouse. The greenhouse was managed by keeping one side as a fruiting area, which could be kept warmer in the winter and the other side was kept as a crib stack cooler resting area. All crib stacks held a tank full of 50 logs so that our fruiting rotation was based on these numbers.

Each rack held 50-60 logs and after soaking they were stacked in these racks and covered with floating row covers which act as humidity blankets. Each rack fruited depending on the ambient temperature and humidity blankets. Each rack fruited depending on the ambient temperature and humidity. The ideal conditions were to maintain a humidity level of 60 to 70 percent by either using the overhead misting fans and at dry times overhead sprinklers or a hand held hose. It was found that misting is very important during the pinning stage of the shiitakes after soaking in the tanks. Shiitake quality and yield were improved. The radiant floor provided an ideal environment for the water to evaporate and improve the humidity in the growing area if needed.

Through use of temperature and humidity monitors, it was very noticeable especially during the winter that with the rising warm air, the region nearest the floor was cooler and that the air nearest the arch of the roof was the hottest. To overcome this heat layering, three large ceiling fans were installed to push the warm air back down towards the logs.

Ventilation during the winter is very important so that a build up of carbon dioxide is avoided. Ventilation is also needed to remove a build up of spores and mold contamination. Crib stacked logs were kept off the floor by using cedar as cedar trends not to rot in a damp environment. Up to 3,000 logs were crib stacked in the greenhouse at one time enabling a rotation of logs to be soaked every 12 weeks. During the spring, some logs were moved from outside into the greenhouse, soaked, and moved outside after fruiting to save on space. It was important not to move a recently soaked log out into bitter freezing temperatures as damage to the log’s bark could occur.

Use of different shiitake strains (WR46, West Wind and Night Velvet) were used in the greenhouse. Logs were soaked in a 12 week cycle up to four times in the first year which is a heavy fruiting cycle. At the end of the year, logs were showing signs of contamination and yields were diminishing -- possibly due to the intense heat (one of the hottest summers on record) and the frequent misting to cool the greenhouse, which may have caused some of the bark contamination. It was originally thought best to fruit the newest logs in the greenhouse in the first year as much as possible and then in the fall, move the greenhouse logs out of the outdoor growing area to rest during the winter dormancy and then use these logs for two outside fruitings for the following year.

This winter 2005-2006, two wide range strains (West Wind and WR 46) are being used to fruit in the greenhouse during the winter/spring and in summer a warm weather strain (Night Velvet) will be used. This will hopefully use the strains that will best match the greenhouse environment for the different seasons.

It is very important to inoculate oak logs as early in the year as possible, so that they will be ready to fruit in the greenhouse for the following fall. Innoculating 4,000 logs last year was not enough logs to accommodate for the greenhouse and the outdoor production was not enough for our first year of production. For the 2006 production year, a 6,000 log goal would provide enough for a full year of fruiting without “burning out” the logs too quickly and provide enough to continue production outside. Due to increase in demand in our mushrooms, we will have to increase production throughout the year.

For this winter's production, crib stacks that are resting in the greenhouse will not be misted and instead a soaker hose has been installed on the ground to maintain humidity in the area and yet keep the logs dry. During severe cold weather, fruiting takes a longer time due to a drop in temperature in the greenhouse and space in the greenhouse can be a problem, so some logs were crib stacked whilst fruiting. Backup heat from the propane furnace as an emergency back up is important although we have rarely used it. The radiant floor slab remains warm for at least a couple of days even if the fire goes out and the wood furnace is easily loaded by hand. Use of a 4-wheel-drive Polaris bike with a flatbed to load, unload and move/soak logs in and out of the greenhouse proved invaluable. The main center gangway in the greenhouse was designed so that the bike and soaking tanks could fit and be near to the center drain. Contaminated logs were moved and burnt and so the wood furnace also acts as a way to dispose of pests and diseased logs efficiently.

Daniel Hellmuth, Architect and Engineer: designed, provided blueprints and specifications and oversaw the construction of the greenhouse.

Dr. Johann Bruhn, Plant Pathologist, University of Missouri-Columbia: consulted on the management and production of the shiitake logs in the greenhouse. Assisted in the design of setting up a possible data collection studying the different strains and how they perform in the greenhouse. Discussions on monitoring temperature and humidity in the greenhouse were discussed. Assisted in the University of Missouri Center for Agroforestry Field Day at the farm and demonstrations.

Rachel McCoy, University of Missouri Center for Agroforestry, University of Missouri-Columbia: Assisted in the mailing and PR for Field Day Open House at the farm, and with editing and writing an article published in "Green Horizons" newsletter.

Gene Ertel, Film and TV Producer Co-operative Video, University of Missouri-Columbia: 10 minute film produced for University of Missouri Center for Agroforestry

Grant Heithold, Scott Material, Licking, Missouri: Heatmor outdoor furnaces. Local business that assisted in the design and choice of furnace and radiant floor.

Joel Oberly, Brighter Homes: design and troubleshoot the maintenance and management of radiant floor.

Jo Krawyzch, Field and Forest Products: consulted on the shiitake strains to use in the greenhouse.

Experimental Proposal by Johann Bruhn

In order to ensure the best use of the greenhouse facility, logs ranging from 10 to 15 cm in diameter will be selected to spend a year in the greenhouse, based on their successful fruiting outdoors by the close of their second season (i.e. their first fruiting season). In this manner, the most productive logs will spend their most productive year in the greenhouse. This strategy also ensures the availability of a winter’s fruiting experience by the final report date.

A split block experimental design will be used to evaluate and compare alternative management practices. Key characteristics of each study log (thickness of bark, sapwood and heartwood and initial dry weight) will be used as covariates in analysis (SAS PROC GLM). The weight of mushrooms produced by each log over the six months will be used as a dependent variable for analysis. The greenhouse will be divided into three equal size statistical blocks. Half of each block will be randomly assigned to each of two force fruiting intervals (e.g. 8 to 10 weeks). Half of each fruiting intervals treatment will be randomly assigned to receive translucent row cover fabric during fruiting to conserve moisture. Half of each row cover fabric treatment will be assigned to each of two wide range strains (West Wind and WR 46). Three logs from each treatment combination in each block (totaling 72 logs*) will be randomly selected for statistical analysis of shiitake mushroom production. These logs will be conspicuously marked and specially tagged so that all mushrooms produced by each of these logs will be collected during normal harvest operations and weighed for analysis.

*3 blocks x 2 intervals x 2 cover treatments x 2 strains x 3 replicate logs = 72 logs

This proposal was tried out, but it proved very difficult on a working farm for workers to pick and weigh and collect the data as it was so time consuming and some of the tags fell off after soaking in the soaking tanks. The farm is three hours drive from the University of Columbia and it was logistically impossible for an assistant to help out daily and proved inefficient for a student to drive down and monitor the experiment. To this date, no hard data was collected, but the potential for future research will still be available to the Department of Agroforestry, University of Missouri Columbia.

Analyzing sales and harvesting records and comparing the 2003/2004 winter (November-March -- which are the coldest months) with the 2004/2005 winter, not only were yields increased, but the cost per lb increased.

Nov 1, 2003-March 31, 2004
690lbs outside fruiting at $8.40/lb
No Greenhouse Production
Gross Sales $5,800

Nov 1, 2004-March 31, 2005
1900 lbs at $8.99/lb
With Greenhouse Production
Gross Sales $17,080

Improvements with record keeping are needed. The budget limitations and the time consuming efforts required to collect data and to train employees proved difficult and were not economically possible on a working farm.

This project established full time work for a local employee, and provided four part-time jobs for innoculation and packaging of value-added mushroom products.

1. Tri State Agroforestry Conference, Keokuk, Ohio, March 2004
2. University of Missouri Center for Agroforestry, filming at OFM Farm for 10 minute film
3. Small Fruit and Vegetable Conference, Springfield, Missouri, February 2005, 205 people attended
4. Field Day at Ozark Forest Mushrooms, April 2005
5. Newspaper articles

This was an excellent opportunity for Ozark Forest Mushrooms to pursue an investment in our enterprise with the addition of a grant to assist in the costs of the wood furnace. The SARE grant certainly became an intricate part to an array of extension people, particularly with the University of Missouri Center for Agroforestry, which provided valuable Public Relations assistance in making this project such a success. This project was certainly mutually beneficial for all parties involved and has led to further outreach. I shall be giving a talk at the University of Missouri-Columbia on February 18, 2006 at the Specialty Mushroom Workshop This involvement has also assisted us in marketing our products and has provided marketing information for our customers and chefs.


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.