Comparing the Profitability of Five Winter Salad Greens Under Heated, Minimally Heated, and Unheated High Tunnel Conditions

Commodities

Practices

The proposed solution to optimizing winter production of salad greens in high tunnels is to systematically evaluate three different high tunnel heating treatments to identify the most cost-effective and sustainable approach for small-scale farmers in the South. The treatments—unheated, minimally heated to 28°F, and moderately heated to 40°F—will be tested on five commonly grown salad greens to assess profitability, environmental impact, and operational efficiency. This project aims to provide Southern farmers with practical strategies for sustainable winter production by collecting and analyzing data on crop growth of five commonly grown greens, yield of each green, labor, row cover usage, and heating costs.

Salad Greens to be Evaluated:

• Salanova® Lettuce
• Esmee Arugula
• Red Russian Baby Kale
• Johnny's Premium Greens Mix (mustards, mizuna, tatsoi, and other brassicas)
• Rangitoto Spinach

Key Objectives:

1. Maximize profitability while minimizing environmental impact
   This project will balance heating and labor costs to identify practices that enhance profitability while reducing the environmental footprint of winter production. The minimally heated treatment to 28°F is expected to offer a balanced solution by potentially reducing heating costs and labor demands while limiting propane use and emissions. In contrast, heating to 40°F may yield higher production but at increased fuel and environmental costs. By examining these trade-offs, the project will provide insights into heating levels that allow for profitability without excessive resource consumption.  Profitability may differ in each of the different crops for each treatment.

2. Evaluate labor and heating trade-offs for each treatment
   Winter growing typically involves labor-intensive row cover management, with row covers needing daily removal in the morning (to prevent excess moisture that can cause disease) and re-application before freezing temperatures each afternoon. The unheated treatment will rely entirely on row covers, requiring significant labor for installation, removal, and daily maintenance. The minimally heated treatment (to 28°F) aims to reduce this burden by eliminating row cover use while still protecting crops from extreme cold (28°F being the minimum temperature at which winter-hardy crops generally avoid damage, as noted by experienced growers Paul and Sandy Arnold). Based on insights from The Winter Market Gardener by J.M. Fortier, heating to 40°F is the lower end of the yield-maximizing range for winter-hardy crops, though it increases heating costs and environmental impacts (though still less than industry-standard 50°F-54°F heating for lettuce). By quantifying labor and heating costs across treatments, this project will enable farmers to make informed decisions on labor and resource allocation for winter production.

3. Enhance seasonal crop production and improve farm stability
   Winter production offers significant benefits for farm income and stability by extending the growing season and allowing farmers to build consistent relationships with customers who value year-round fresh produce. This project will demonstrate the impact of various heating levels on yield and profitability, offering a framework for winter growing practices that create opportunities for steady farm employment, reduce seasonal turnover, and support consistent revenue. Furthermore, expanding winter production helps farms gain a competitive edge by supplying high-demand crops during the off-season, strengthening their position in the local market.

4. Improve environmental sustainability
   A critical component of this project is minimizing the environmental impact of winter production. High tunnel heating extends the growing season and increases yields, but it requires energy, typically from propane. By evaluating different heating levels, this project will examine the trade-offs between maximizing yield and reducing fuel consumption. The minimally heated treatment—using propane to maintain a temperature of 28°F—presents a promising option for reducing heating costs and minimizing the environmental impact. This approach will be especially relevant for small-scale farms that aim to enhance sustainability without compromising economic viability.

Expected Outcomes:

• Profitability analysis: By comparing the yield, labor, and heating expenses for each treatment, this project will provide insights into which heating strategy offers the best return on investment. We hypothesize that the minimally heated treatment may provide a cost-effective balance between yield, labor, and heating expenses, potentially maximizing profitability while minimizing environmental impacts.

• Sustainability analysis: This project will contribute to the development of sustainable practices for winter growing, examining how small farms can optimize high tunnel usage while reducing dependency on fossil fuels. The research will offer actionable recommendations for minimizing emissions and resource use, helping farmers achieve profitability with a reduced environmental footprint.

• Labor and operational efficiency: By comparing labor requirements across treatments, this project will help farmers streamline winter operations, identifying labor-efficient strategies that also support year-round employment. Enhanced winter production could provide steady employment for farm teams, reducing turnover and offering continuity for seasonal staff.

Overall Solution Impact:

This project’s solution—optimizing winter growing with targeted high tunnel heating strategies—will benefit small-scale farmers and the broader food system. By improving winter production practices, farmers can increase income, stabilize operations with reliable year-round labor, and reduce environmental impacts, all while meeting growing demand for fresh, local produce in the off-season. The data and insights generated by this project will contribute to a more sustainable, profitable, and resilient agricultural system that supports farmers, consumers, and rural communities.

Research Design

The project will take place over two winter seasons (October to February) in three identical 30' x 96' Rimol Nor'Easter high tunnels with double inflated poly and automatic roll-up sides at Crooked Porch Farm. Each high tunnel will be randomly assigned one of three treatments: unheated, minimally heated to 28°F, and moderately heated to 40°F. In the second year, each treatment will be randomly reassigned to a different tunnel to c

ontrol for tunnel-specific variables. We will grow and measure five salad greens grown on our farm and many other small-scale, year-round farms: Salanova® Lettuce, Esmee Arugula, Red Russian Baby Kale, Johnny’s Premium Greens Mix, and Rangitoto Spinach. Soil preparation, fertilization, and irrigation will be kept consistent across all treatments to ensure reliable comparisons. SARE Proposal Trial Replication Diagram

Methodology

1. Soil Preparation

To control for potential soil nutrient differences from past crop rotations, we will sample the soil in each tunnel and submit it to the University of Maine’s High Tunnel Soil Testing Program. Following the soil test results, organic amendments will be added to meet nutrient requirements as outlined in the Mid-Atlantic Commercial Vegetable Production Recommendations. We will prepare the beds using our standard farm practices, including broad forking to loosen the soil and using a tilther for a smooth seeding surface. This method ensures consistent soil structure across treatments, allowing crop performance differences to be attributed to heating treatments rather than soil variability.

2. Planting

All crops will be planted on the same day according to standard practices at our farm. Salanova® lettuce will be transplanted into landscape fabric at 6-inch spacing, while the other greens will be direct-seeded with a Jang Seeder. Seed will be weighed before and after seeding to ensure reliable seeding rates. We will plant the center five beds of each of the three high-tunnel treatments to reduce edge effects.  Each bed will be divided into five 18' sections, one for each green. The order of these plantings will be cycled through the tunnels to account for variability in conditions across the growing space (see attached diagram).

3. Temperature Control and Monitoring

Each high tunnel will have temperature-monitoring systems to maintain and track the internal climate. Propane heaters will be used to maintain nighttime temperatures to a set point of 28°F in the minimally heated tunnel and 40°F in the moderately heated tunnel, while the unheated tunnel will rely on passive solar heating and row covers. The Orisha monitoring and control system will automatically control roll-up sides in each tunnel according to external weather conditions, while maintaining the minimum nighttime set point. Automation is important in this project to maintain similar day-time and max-temp conditions in each of the three trials.Temperature data loggers will record hourly readings both under row covers and within the high tunnel to capture precise temperature conditions for each treatment.

4. Crop Growth and Yield Measurements

• • Growth: Each Wednesday we will measure leaf size and plant height for direct-seeded greens, as well as Salanova® lettuce head diameters, across the five sections per bed, totaling 25 measurements per tunnel. Regrowth will be evaluated after each harvest to assess recovery rates.
  • Harvest and Yield: Every Thursday we will harvest the entire "section" in each area that has reached marketable height or diameter. We will weigh each green separately and record yield data.

5. Labor Inputs

Labor will be tracked separately for each treatment, specifically monitoring:

• • Row Cover Management: In the unheated treatment, labor for daily installation and removal of row covers will be recorded.
  • General Crop Care: Routine tasks such as irrigation, weeding, and pest management will be recorded, though these will be similar across all treatments and will not be expected to vary significantly. .

6. Heating Costs and Environmental Impact

Propane use will be monitored weekly by recording the gallons consumed in each heated tunnel. We will calculate heating costs based on local propane prices and use propane consumption data to estimate the carbon emissions associated with each treatment. This will enable us to assess the environmental impact of each heating strategy in terms of both cost and emissions.

Data Analysis

We will compile and analyze all collected data to evaluate each treatment based on:

• Yield (Marketable Weight): Comparing yields across treatments will show if and how heating improves productivity, helping us understand the financial viability of each approach when accounting for labor and heating costs.
• Labor Efficiency: Total labor hours will be calculated for each treatment to identify the most labor-efficient strategy, beneficial for small-scale farms with limited labor resources.
• Heating Costs and Environmental Impact: Propane consumption data will be used to calculate heating costs and estimate carbon emissions, clarifying the environmental and financial trade-offs of each treatment.
• Profitability: The total cost (labor, heating, materials) will be compared to the total yield to calculate the cost per pound of each crop. This will provide a direct comparison of profitability between treatments.

Expected Outcomes

This research will yield essential insights for winter salad green production in high tunnels:

• Profitability: We expect to identify the heating treatment that balances yield, labor savings, and heating costs for optimal profitability.
• Environmental Sustainability: Minimally heating to 28°F is anticipated to yield a lower environmental footprint by limiting propane use while protecting crops from frost, presenting a sustainable option for winter production.
• Improved Winter Production Practices: The data will provide actionable insights into heating, labor, and yield trade-offs, allowing small-scale farmers to optimize winter resource allocation.

Conclusion

By systematically evaluating heating levels, labor demands, crop yield, and environmental impact, this project will identify the most sustainable and cost-effective winter growing practices for small-scale farms. The findings will directly benefit farmers in the South by improving profitability, labor efficiency, and environmental sustainability, supporting resilient, year-round food systems.