Final report for FNC21-1277
Roots, Fruits and Shoots, LLC, is a three acre raspberry and vegetable farm. The farm was started in 2019. Most vegetables are grown for winter sales. We grow storage crops in the field and leafy greens in high tunnels all winter. The farm uses organic practices and switched to a no-till system in 2020. We have permanent beds that we mulch with compost and try to keep covered (by growing plants -either cash or cover crops) year-round.
Growing cold-tolerant crops in high tunnels during the winter is a low-input strategy to provide farmers additional revenue and improve farm cash flow, but there is limited information available about the cost/benefit of different management approaches to moderating the sub-freezing temperatures common during this season. We are interested in understanding whether the investment in supplemental heat to minimally heat a winter tunnel is economically viable. This project will evaluate the use of two different management practices - supplemental heat and row covers - in high tunnels on spinach and kale grown during the fall-winter at a farm located in Johnstown, Ohio. Crops will be planted across three dates in each planting cycle, enabling us to determine whether supplemental heat could allow for later fall plantings of winter harvested crops. Results from the trials will be presented through a local conference and on-farm tours, which we will publicize in collaboration with local service providers. A report of the results will also be posted on the farm’s website. These results will provide high tunnel farmers with information necessary to make informed decisions about infrastructure investments for winter high tunnel growing which can improve farmer quality of life and the farm’s bottom line.
- Evaluate the effect on yield and revenue when providing supplemental heat versus row cover to fall/winter high tunnel crops seeded throughout fall/winter.
- Determine the economic costs and management hours of using supplemental heat versus row cover for winter high tunnel crops.
- Share findings with other winter tunnel users and farmers in the Upper Midwest through conference presentations, field days and an online report.
Two single-layer high tunnels (30x48’ and 20x48’) will be used in this trial. Each tunnel will be divided widthwise into three equal sections (Sections 1, 2 and 3) using Solarig plastic sheeting. One tunnel already has a heater and a second heater will be installed in the second tunnel using grant funds. These heaters will be mounted in Section 1 and will be set to 35 degrees, the base temperature for growth for crops grown. The adjacent section (Section 2) of the tunnel will benefit from the ambient heat, and I expect it will stay relatively warmer than if no heat was used. Section 3 will not be heated and row covers will be used when temperatures are projected to be below 32 degrees at night - currently my standard practice. Temperatures in each section will be monitored using temperature sensors to confirm differences.
Two crops - lacinato kale and spinach - will be planted in each tunnel using standard seeding rates and transplant spacing. Using two crops allows us to see how supplemental heat affects high-value crops at different ends of the cold-hardiness spectrum - spinach is an incredibly resilient, cold-hardy crop; the variety lacinato kale is more tender.
Each crop will be planted on three different dates two weeks apart (September-October). We will repeat this planting cycle in 2021 and 2022 to see if the results are consistent across variations in weather from year to year. Both crops are usually planted in September into high tunnels in the Upper Midwest in order to mature for harvest during the winter - these dates will test how supplemental heat can delay those planting dates.
The following data will be collected:
- Temperatures in each section
- Labor hours
- Input costs
- Utility costs
Experimental Layout: NC SARE FRG Experimental Design
Midway report- The dividers were installed in the early fall and crops were planted. We did have some large rains in October, which washed out crops in one high tunnel, and some issues with a compost used in that same tunnel, so I don't know that the results from that tunnel will be useful this year. There was also a delay in getting the temperature sensors because of shipping delays, so I didn't install those until early December 2021. The other tunnel's experiment is going well and is on schedule. I've been harvesting crops in that tunnel since December, and have been logging harvests in a sheet I created for this experiment. I'll take a look and analyze the data for the first year beginning in March.
One note - it was so warm in November and December 2021, that I didn't even need internal row covers until January 2022. It will be interesting to see how that compares with results if in 2022 we have a colder November/December.
Our results for year 1 were as follows:
- Lacinato Kale:
- 30% greater yield for kale plants in 35F compared to unheated
- 5% higher yield in 35F compared to 30F section
- 36% higher yield for spinach in 35F compared to unheated
- 22% higher yield in 35F compared to 30F zone
- Heated – cost (extrapolated for full tunnel): $1,561.97
- Included propane, electric
- Unheated – cost (extrapolated for full tunnel): $1,282.50
- Included labor to cover/uncover and commute to farm, plus mileage
- Excluding mileage, was $557.50
- 21% more cost for unheated than heated ($279.47)
- Excluding mileage, cost was $1,004 more
- For us in this tunnel, we would need to generate $6.51/bed ft ($1.16 more than unheated) to make up additional costs.
- Kale - For our winter markets and CSA, where lacinato kale sells for $5/lb (sometimes higher), we would need to produce 1-1.3 lb/bed ft.
- Spinach – avg for spinach is $13.85/lb in winter, we would need to produce 0.47 lb/bed ft.
- In 2021, even in low yield year, produced 2.975 lb/bedft kale and 1.34 lb/bedft spinach.
Year 2 results-
We are still able to harvest, so yield data isn't complete, but currently Year 2 trends follow Year 1. Kale yields are 12% higher in the 35 degree heated tunnel compared to the unheated, and 6% higher in the heated. We expect those differences to increase by end of February. Spinach yields are also 11% higher in the heated compared to unheated, a difference we expect to increase even more going into February. Late planted kale had a 97% higher yield in the heated tunnel compared to unheated, and a 25% higher yield in the moderately heated tunnel compared to the unheated to date.
Educational & Outreach Activities
On 11/6/22, I hosted a farm tour through the Ohio Ecological Food and Farm Association (OEFFA) to highlight the results of year 1 and show the second year of the project in progress. Over 50 people attended the event. I also was selected to present my results at the OEFFA conference in February 2023, where I anticipate at least another 20 people in attendance.
Here is a copy of my powerpoint from my presentation in February, 2023 at the OEFFA conference:
Here is a link to the farm tour series brochure: https://www.oeffa.org/news/farm-tours-2022/ and 2023 conference program https://conference.oeffa.org/
I am in the process of creating a factsheet and intend to distribute it at the OEFFA conference in February 2023.
Installing the barriers does cut down on air flow in the tunnel. Managing the humidity has been an ongoing concern that I've had to address by venting the tunnel using the sidewalls more than I otherwise would.
While I have not yet analyzed data from the first year, as I am still collecting data, it does look like the heat may have allowed for later plantings to still reach maturity and produce a good harvest through the winter. It would be interesting to evaluate whether heating the tunnel even more in the fall (say to 45 degrees at night) would further encourage this growth and give me more time to plant a winter crop in the high tunnel.
Supplemental heat is not required for winter growing, but can be more profitable. Supplemental heat has a significant impact on plant growth during the winter, even during time periods of low light (December/January). The yield increases with heat outweighed the costs of propane. We also discovered that compared to using row cover, supplemental heat was more profitable (calculated looking at all the costs associated with both methods and comparing to revenue). Both the low heated treatment and the higher temperature treatment proved to be beneficial in significantly increasing yield and we didn't see large differences between the 30F treatment and 35F treatment in terms of yield.
On a crop by crop comparison, heat made a bigger difference for lacinato kale, than spinach, and also improved the quality throughout the winter. For lacinato kale, that meant less tipburn. Heat still made a difference with spinach, and that difference was enough to offset heating costs. Yield was still lower for later planted crops than earlier planted crops, but the difference for kale was much less in the tunnel with supplemental heat (about 70% of earlier planted kale in the warmest section, compared to 50% in unheated).
This study also could have a number of follow up studies: benefits of different heat sources, increasing the minimum heat in a tunnel or targeting the timing of that heat (for example, in the early morning hours to allow plants to thaw/warm up faster), testing more crops, evaluating later planting dates.
Midway Report: I haven't done outreach yet, so have not interacted with many farmers yet regarding the results. However, I have told many farmers in passing that I'm working on this project, and they were really excited to see the results and also felt like there was a need to understand the cost/benefit of using supplemental heating for high tunnels.
Final Report: Over 50 people attended the farm tour I hosted in the fall on this topic, showing significant interest in the topic. As a result of that tour, I followed up with a couple small scale vegetable farmers that attended the tour. I visited their farms to learn more about their systems and experiences with supplemental heat.
Testing more temperature trials (such as heating to higher temp at different times of year) and timing of heating (such as in the morning, to thaw out crops that froze overnight and allow them to photosynthesize earlier) would be great topics for future study. Also testing additional crops would be beneficial.