Final report for FNC21-1291
Student Managed Farm at University of Michigan entering our 10th season of production. We are a 10 acre farm with 3 acres in mixed vegetable production for primarily wholesale institutional markets. We have 13,000 sqft of hoop house space and 3000 sqft of heated transplant production space.
This project was conducted to evaluate the feasibility of mushroom production as a stacked use function with transplant production in a heated greenhouse, where mushroom production occurs under transplant production tables in space not normally utilized/occupied. Potential for stacked use or synergistic production systems that more fully utilize fixed assets/resources in small farming operations has the ability to increase the economic and environmental sustainability of such operations by generating more food production and economic activity from existing heated transplant production spaces thereby increasing carbon and capital use efficiency. The project evaluated different mushroom species/strains (Oyster, Wine Cap, and Shiitake) as well as production techniques to assess their suitability for use under transplant tables in heated transplant production greenhouses. This analysis included evaluation of yield, as well as economics of labor, material costs and potential revenues. Results have been distributed to area and regional farmers through an educational “zine,” or handbook detailing methods, findings, and recommendations.
We grew three different types of mushrooms (Wine Caps, Shiitakes, and Oysters) in a heated greenhouse beneath transplant production tables. These varieties were selected because the inoculum are relatively inexpensive, heat tolerant/loving strains exist, are relatively quick to fruit, and have competitive market prices (each at about $5-10/lb). We grew these three varieties with a total of five different “treatments” with three replicates of each treatment: Treatment 1: shiitakes will be grown only on logs; Treatment 2: oysters in totems; Treatment 3 oysters on logs; Treatment 4 wine caps on chipped invasive (buckthorn) substrate; Treatment 5: wine caps on straw. We began the process of all five treatments in the spring of 2021, and watched them throughout the summer and fall. By December of 2021, we had not seen many results from the treatments listed above, however, still had 6 months to work on our project. Wine caps on straw substrate was the fastest growing and least resource dependent, so we decided to inoculate three more beds. The next months involved lots of transplant production at the Campus farm, so we hoped that the increase in frequency of watering would lead to more moisture available to the mushrooms. By June, we realized that no mushrooms were going to grow, and began gathering what we had learned to compile into our handbook for distribution to farmers.
For a farm of our size and due to other staff and resource restrictions, this type of mushroom production may require too much hands-on maintenance, and be more feasible for a non-diversified farm with transplants on a table in the greenhouse for most of the year.
Though we have not yet distributed our educational zine to nearby, small farms, our tour and workshop inspired other student farmers to experiment with mushroom cultivation.
- Evaluate feasibility of growing mushrooms under transplant production tables in heated greenhouses.
- Identify which mushroom types and production systems work best in this environment (wine caps mushrooms on straw or wood chips; oyster mushrooms in totems or in logs; shiitake mushrooms in logs).
- Evaluate potential economic benefits from this stacked/dual use system that utilizes previously un-utilized space to offset greenhouse heating costs, diversify production and increase economic and environmental sustainability.
- Disseminate findings and recommendation to farmers in our area though field day and further with a digital workbook detailing techniques, findings and recommendations.
We will be growing three different types of mushrooms (Wine Caps, Shiitakes, and Oysters) in a heated greenhouse beneath transplant production tables. These varieties were selected because the inoculum are relatively inexpensive, heat tolerant/loving strains exist, are relatively quick to fruit, and have competitive market prices (each at about $5-10/lb). We are growing these three varieties with a total of five different “treatments” with three replicates of each treatment: Treatment 1: shiitakes will be grown only on logs; Treatment 2: oysters in totems; Treatment 3 oysters on logs; Treatment 4 wine caps on chipped invasive (buckthorn) substrate; Treatment 5: wine caps on straw. Please see the attached schematic drawings to visualize these plans.
To communicate our findings to other small, organic diversified vegetable farms, we created a physical zine, or small-self published educational magazine, for stacked functionality mushroom growing under transplant production tables in heated greenhouses. We also held an educational tour for farm volunteers including a hands-on demonstration of our wine cap bed inoculation process.
Our stacked functionality mushroom production project resulted in lower yields than anticipated. Over the course of the project, we only harvested a total of ten shiitake mushrooms from the plugged logs after using the force-fruiting method, of 25.5 grams on average and cap diameters of around 3 to 4 inches. Below is a table including the masses of ten shiitakes harvested on December 15, 2021.
We also saw only a few wine cap mushrooms successfully fruit out of the straw beds. On January 21, 2022, we harvested two wine cap mushrooms, one weighing in at 73 grams, and another at 9.1 grams.
While the sizes/masses of the mushrooms we produced are similar to those produced on a commercial level, Compared to commercial mushroom growth in controlled environments, such as inside of a freight/shipping container, these yields are very low. In a project for Cornell’s Small Farms Program, Steve Gabriel offers the estimate that for every 5 pounds of substrate spread, one can expect a total mushroom yield of 1 pound. Adding up our total substrate for the project, we used approximately 160 lbs, and could have, under ideal conditions, expected 32 total pounds of mushrooms. However, we only experienced 350 grams, or about 0.8 pounds of edible mushroom production. This shows that many factors, which will be discussed in our lessons learned section, affected our production efficiency.
Educational & Outreach Activities
We held 1 tour at the UM Campus Farm for folks to see and hear about the project. We also created a Zine that detailed the project ideas, methods, results and recommendations that we are distributing to farmers at the Ann Arbor Farmers Market and Argus Farm Stop as well as electronically to local farmer email lists and on the UM Campus Farm webpage.
A year and a half after our first inoculation, we gleaned many lessons about stacked functionality mushroom production in greenhouses. Our first inoculations of mushrooms occurred in April 2021, based on grant timeline and availability of the funds. This was two months later than we had imagined for optimizing the dual use of the greenhouse for mushrooms and transplant production. One effect of this delayed timing was that greenhouse temperatures were warmer for the spawn run and by early June the number of transplants covering tables and being watered was greatly reduced as warm season crops were planted into the field. This later and warmer window subjected the different mushroom treatments to hotter and drier conditions that were less ideal for mycelium growth. This was particularly true for the oyster mushrooms both in totems and on logs. We did observe significant initial mycelium growth in wine cap beds on straw and wood chips in June and by August, the totems were showing significant mycelium growth so we removed their plastic coverings. However, those mushrooms ended up aborting their growth we believe due to high temperatures and drying conditions of the greenhouse in July and August. During July and August there were still some transplants in production and staff watering transplants would spray water under the tables daily to try and help increase moisture content. This turned out to be insufficient for oyster totems and too much water for the wine caps both on straw and on wood chips which seemed after achieving a good mycelium run to rot rather than fruit. In December when we began washing and packing produce in the greenhouse from our hoop houses and cold storage we noticed that the shitake logs started to fruit but only at the bottom of the logs. We speculated that this was either due to higher moisture levels on the ends touching the wet soil under the table and or that the mycelium runs in the logs may have only been able to colonize the bottom portion of the logs as the top portions may have become to dry under the hot and dry summer greenhouse conditions. To test to see the mycelium runs had been good in the logs but that insufficient moisture for fruiting was inhibiting logs from fruiting farther up the logs we soaked logs in water for 24-48 hrs to force fruiting.
This was successful in getting some fruiting along the entire length of the logs but yields were small (ten shiitakes, recorded in Results and Discussion). We also decided to re-inoculate the wine cap bed in December and added 3 additional 16-foot-long wine cap beds on straw in February and another in March. After waiting two months for the spawn run, however, the conditions in the greenhouse already proved too hot and dry for fruit, even for the warm-weather strain we used, and we saw no fruit.
Things we have learned:
- Timing of inoculation is likely critical as it greatly affects temperatures and moisture levels in the greenhouse, with some seasonal fluctuations being amplified by the greenhouse conditions. Inoculating logs, totems or wine cap beds in the fall in our region starting possibly in October when temperatures in our region are lower and when the greenhouse is no longer in transplant production might possibly allow for better and longer spawn run during fall and heading into winter. This shift in timing might allow for fruit production once the heated greenhouse is fired back up for transplant production in January or February. Inoculation in early, mid or late winter did not provide good results in our experiment. Shade cloth should be used to cover tables when numbers of transplants are insufficient to keep mushroom production areas covered. This will reduce drying of the wood and or straw.
- If adding supplemental moisture to wine cap beds, careful observation to only add extra water when needed should be taken.
- Inoculated logs should likely be kept in a non-fruiting position during mycelium runs. This means they should be laid on the ground to encourage more uniform moisture content and greater ability to effectively add moisture and then shifted to fruiting positions after soaking. Having some under table greenhouse space reserved as fruiting space would likely be ideal.
- Since soaking/forcing is likely necessary for logs under greenhouse conditions choosing smaller diameter logs in the 4 inch range may be more ideally suited.
- Our farm does not have transplants on the tables above the mushrooms at all times, so mushrooms need to be monitored and given supplemental water and shade as needed. Small diversified farms are busy and often tight on resources. Where possible earning additional revenue from enterprises that can take advantage of existing staffing and physical infrastructure to generate extra income is helpful. This works best when the extra effort is marginal relative to base operation and the extra income generation is relatively substantial. With this project we theorized that mushroom production under transplant tables would be such an example. In reality the mushrooms did not prove successful under this management approach. As mushroom farmers I am sure would attest, growing mushrooms like any other horticultural crop requires a fair bit of attention to do it well. On our busy vegetable farm with vegetable and transplant production as primary objectives we attempted to pick a few varieties and production techniques we thought would do well with little management under our transplant tables. Based on the timing of our trials it appears that much more active management of the mushroom productions in the greenhouse environment is required for success. In fact due to the excess heat during summer months higher degrees of management and care seem to be necessary than in other more conventional production systems. As we suggest above it may be possible by shifting inoculations dates into the early fall to gain better success. Where wine cap runs on straw would finish during the spring after a one time run, or where smaller shiitake logs were left under tables and pulled out in forced fruiting events.
Several area farmer have expressed interest in this novel approach, however our limited success did not help foster immediate adoption, we feel that the lessons learned and tips/recommendations shared in the zine will provide farmers looking to try this method with greater chances of success.
In general, we have concluded that mushroom production in a greenhouse necessitates extra labor and resources specifically for the mushrooms; this type of mushroom cultivation is much less passive than we initially thought. If you are a farmer looking to diversify your income during slower seasons with mushroom cultivation in greenhouses, we would recommend growing shiitake mushroom plugs in logs or wine cap mushrooms in a bed of straw. Both of these varieties will require extra care such as ensuring they have shade and are moistened regularly. You may also stimulate shiitake fruiting by “force fruiting,” or soaking the logs a couple weeks after inoculation for between 24 and 48 hours to re-wet the log. It could also be possible that this type of mushroom production would be better suited to a farm that does not have diversified production, meaning that there is always one type of transplant on transplant tables above the mushrooms, getting consistently watered and offering shade to the mushrooms. Growing mushrooms at a farm like this could mean that the production might be less hands-on.
Recommendations for future study would include: testing fall inoculation dates for winecaps on straw, longer term study with smaller shiitake logs (possibly fall inoculated) left in spawn run stacks under tables and pulled out for forced fruiting, testing of either of the above in more commercial greenhouse operation focused on transplant production that provides more uniform table cover and watering regime, modification of the system to include micro-misters undertables to better control moisture and temperature particularly during the warmer months.