Extend Your Growing Season: A Guide to Greenhouses & High Tunnels for Organic Farms

For organic farmers, the rhythm of the seasons dictates much of the work. The short growing season in many regions presents a significant challenge, limiting the amount of fresh produce that can be harvested and sold. However, the implementation of greenhouses and tunnels offers a powerful solution, allowing for the extension of the growing season well beyond traditional limits. These structures, when used correctly, not only increase yields but also create opportunities for year-round production, a major advantage for organic agriculture. This detailed guide explores how organic farmers can leverage greenhouses and tunnels to their fullest potential.

Understanding the Basics: Greenhouses vs. Tunnels

Before delving into the practical applications, it’s crucial to understand the difference between greenhouses and tunnels, also known as high tunnels or hoop houses. While both structures aim to create a controlled environment for plants, they differ significantly in terms of construction, cost, and functionality.

Greenhouses

Greenhouses are typically permanent structures made of glass, polycarbonate, or polyethylene film supported by a frame of metal or wood. They often include advanced features such as automated ventilation, heating, and lighting systems. Key characteristics include:

• Durability: Greenhouses are built to last, with materials that withstand harsh weather conditions.
• Climate Control: They offer a greater degree of control over the growing environment, allowing for precise adjustments of temperature, humidity, and light.
• Cost: Building a greenhouse typically involves a higher initial investment due to the more complex design and materials used.
• Versatility: Greenhouses are highly versatile and can accommodate a wide variety of crops, including taller plants and even hydroponic systems.

Tunnels (High Tunnels/Hoop Houses)

Tunnels are simpler and more affordable structures made of hoops (usually metal) covered with a layer of plastic film. They do not typically have complex climate control systems, relying more on passive ventilation. Key characteristics include:

• Affordability: Tunnels are less expensive to build and maintain, making them more accessible to smaller organic farms.
• Simplicity: The design is straightforward, allowing for relatively quick assembly and relocation if needed.
• Passive Climate Control: Ventilation is primarily achieved by rolling up the sides of the plastic cover, making them less energy-intensive.
• Season Extension: Tunnels are highly effective in extending the growing season by providing protection from frost, wind, and heavy rain.

Table 1: Key Differences Between Greenhouses and Tunnels

Why Extend the Growing Season? Benefits for Organic Farmers

Extending the growing season through the use of greenhouses and tunnels offers numerous advantages for organic farmers:

1. Increased Yields: By extending the growing season, farmers can harvest crops earlier in the spring and later into the fall, leading to a significantly higher overall yield.
   • Example: Tomatoes started in a greenhouse can be ready to harvest weeks before field-grown tomatoes, allowing farmers to capitalize on early market prices.
2. Improved Crop Quality: The protected environment in greenhouses and tunnels shields plants from harsh weather conditions, such as frost, hail, and heavy rain. This can lead to better-quality fruits and vegetables, with fewer blemishes and damage.
   • Example: Lettuce grown in a tunnel is less likely to be damaged by hail or wind, resulting in more marketable heads.
3. Reduced Pest and Disease Pressure: While not eliminating pests and diseases entirely, greenhouses and tunnels can reduce exposure to many common agricultural problems. This is particularly beneficial for organic farmers, who prioritize natural pest control methods.
   • Example: The covered environment can minimize the impact of certain insect pests and airborne fungal diseases, allowing for more natural control methods.
4. Seasonality Gaps: Extending the season allows you to meet market demands when other producers are out of season. This can result in premium prices and improved customer loyalty.
   • Example: Providing locally grown produce like spinach or kale during the winter months can command higher prices.
5. Year-Round Production: In some regions with the help of heating and appropriate crops, greenhouses facilitate the harvesting of certain vegetables and herbs throughout the whole year.
   • Example: Using a heated greenhouse, it is possible to grow crops like salad greens, herbs, and microgreens even in colder winter months.

Implementing Greenhouses and Tunnels in Organic Farming

The successful use of greenhouses and tunnels requires careful planning and management. Here are some key considerations for organic farmers:

Site Selection

The location of your greenhouse or tunnel is critical for optimal performance:

• Sunlight: Choose a site that receives maximum sunlight throughout the day, ideally with a south-facing orientation. This will maximize photosynthesis and the natural heating potential.
• Drainage: Ensure that the site has good drainage to avoid waterlogging, which can lead to root diseases. Avoid low-lying areas where water may accumulate.
• Accessibility: The site should be easily accessible for both construction and ongoing maintenance, including water sources and easy transfer of crops.
• Wind Protection: Although tunnels and greenhouses offer protection against wind, choosing a location sheltered from prevailing winds can reduce stress on the structure and heat loss, and prevent structural damage.
• Proximity to Utilities: Consider the proximity to water sources and potential electrical access for heating or ventilation.

Material Selection

Choosing the right materials for your greenhouse or tunnel is crucial for its longevity and efficiency:

• Frame: For greenhouses, opt for durable materials like galvanized steel or aluminum. For tunnels, metal hoops are common, but for larger tunnels, galvanized steel can improve the structure's strength.
• Covering: Polyethylene film is a popular choice for both greenhouses and tunnels due to its affordability and ease of installation. However, for greenhouses, consider UV-treated polycarbonate panels for added durability and light transmission.
• Ventilation: For greenhouses, automated ventilation systems can ensure optimal temperature and humidity levels. For tunnels, simple roll-up sides or end vents can provide adequate ventilation.
• Flooring: Consider a proper flooring material such as gravel or weed barrier to improve drainage and reduce weeds.

Soil Management

Maintaining healthy soil is vital for organic production within greenhouses and tunnels:

• Soil Testing: Regularly test the soil to determine nutrient levels and pH, making adjustments as needed.
• Organic Matter: Incorporate plenty of organic matter, such as compost, into the soil to improve fertility and drainage.
• Crop Rotation: Rotate crops to prevent the buildup of pests and diseases. This is especially important in enclosed environments.
• Raised Beds: Consider using raised beds to improve drainage and soil management, making it easier to manage within the structure.
• Fertilizers: Only use organic certified fertilizers to nourish the soil.

Crop Selection

Choose crops that are well-suited to growing in a protected environment:

• Early and Late Season Crops: Focus on crops that can be planted earlier in the spring and later into the fall, such as leafy greens (spinach, lettuce, kale), root vegetables (carrots, radishes), and some fruiting vegetables (tomatoes, peppers).
• Heat-Loving Crops: In greenhouses, you can extend the season of heat-loving crops like tomatoes, peppers, and cucumbers, which thrive in the warmer environment.
• Winter Crops: Select winter-hardy varieties of leafy greens and root vegetables for fall and winter harvests.
• Consider Market Demands: Choose crops that have a market demand.

Pest and Disease Management

Organic farmers should prioritize preventative measures and natural pest control methods:

• Sanitation: Keep the greenhouse or tunnel clean and free of plant debris to prevent the spread of pests and diseases.
• Beneficial Insects: Introduce beneficial insects, such as ladybugs or lacewings, to control common pests.
• Companion Planting: Use companion planting techniques to deter pests and attract beneficial insects.
• Organic Sprays: Use organic pest control sprays, such as neem oil or insecticidal soap, as needed.
• Air Circulation: Good air circulation can prevent fungal diseases and reduce humidity levels.
• Rotate Crops: Following proper crop rotation techniques reduces the risk of disease buildup and pest infestation in the closed environment.

Environmental Control

Monitoring and managing the growing environment is essential for success:

• Temperature: Monitor temperature levels and make adjustments as needed, using ventilation or heating systems as required.
• Humidity: Control humidity levels by ensuring adequate ventilation. High humidity can promote fungal diseases, while low humidity can lead to water stress.
• Light: Ensure plants receive sufficient light, supplementing natural light with artificial grow lights when necessary.

Water Management

Proper watering practices are critical for plant health:

• Drip Irrigation: Install a drip irrigation system to deliver water directly to the roots, reducing water waste and minimizing foliar diseases.
• Watering Time: Water early in the day to allow plants to dry before nightfall, reducing the risk of fungal diseases.
• Water Quality: Use clean, high-quality water for irrigation, free from contaminants.
• Monitoring Soil Moisture: Regularly check soil moisture to prevent overwatering or underwatering.

Specific Strategies for Season Extension

Here are some practical techniques to maximize the benefits of greenhouses and tunnels:

1. Starting Seedlings Early: Begin growing seedlings in the protected environment of a greenhouse or tunnel in late winter or early spring, weeks before they can be planted outdoors. This will give your plants a significant head start.
   • Example: Start tomato seedlings in a greenhouse in late February, then transplant them into the field or tunnel in late April or early May.
2. Extending the Fall Harvest: Plant late-season crops in the greenhouse or tunnel in late summer to continue harvesting well into the fall.
   • Example: Plant spinach or kale in a tunnel in late August or early September to harvest well into December.
3. Double Cropping: Plant early maturing crops followed by late-season ones, thus optimizing space and efficiency.
   • Example: Plant radishes or spinach in early spring and follow with heat loving crops like tomatoes in summer and again leafy greens in the late fall.
4. Winter Production: With proper insulation and heating, some greenhouses can be used for winter production, providing fresh produce even during the coldest months.
   • Example: Grow salad greens or herbs in a heated greenhouse during the winter months.
5. Using Row Covers: Use row covers within the greenhouse or tunnel for added protection against frost or pests.
   • Example: Drape row covers over tomatoes in the tunnel during a late spring frost, providing extra protection.
6. Using Thermal Mass: Incorporate thermal mass materials like water drums or dark-painted concrete to store heat during the day and release it slowly at night.
   • Example: Place barrels filled with water inside the greenhouse, which absorb heat during sunny hours and release them when the temperature drops at night.

Sustainable and Organic Practices

When implementing greenhouses and tunnels, organic farmers should prioritize sustainable practices:

• Water Conservation: Utilize efficient irrigation methods, such as drip irrigation, to conserve water.
• Energy Efficiency: Design structures that maximize natural sunlight and ventilation. Consider using solar panels to power ventilation systems or other energy needs.
• Composting: Compost all plant waste to recycle nutrients and reduce waste.
• Biodegradable Materials: Opt for biodegradable materials for mulching, and other aspects whenever possible, reducing the environmental impact.
• Seed Saving: Save seeds from successful plants grown in the greenhouse or tunnel for future plantings, developing varieties that are well-suited to the environment.

Conclusion

Extending the growing season with greenhouses and tunnels is a valuable strategy for organic farmers. By carefully planning, implementing, and managing these structures, farmers can significantly increase yields, improve crop quality, and enhance profitability. This comprehensive guide should enable you to harness the power of these controlled environments, ensuring a successful, productive, and sustainable organic farming operation. Remember to always tailor the practices to your specific climate, soil, and crop needs, while continuously seeking new knowledge to further optimize your systems.