Growing food year-round in an underground greenhouse, also known as a walipini or pit greenhouse, is an innovative and efficient way to maintain a stable growing environment regardless of external weather conditions. Here’s a guide to help you understand and build an underground greenhouse to enjoy fresh produce throughout the year.
Why Choose an Underground Greenhouse?
Temperature Regulation: The earth’s natural insulation helps maintain a consistent temperature, protecting plants from extreme cold or heat.
Energy Efficiency: Reduced need for additional heating or cooling lowers energy costs and environmental impact.
Extended Growing Season: Grow crops that typically require warmer climates even during colder months.
Water Conservation: Lower evaporation rates due to stable temperatures and humidity levels.
Steps to Building an Underground Greenhouse
1. Selecting the Site
- Location: Choose a site with good sun exposure, ideally on a south-facing slope to maximize sunlight.
- Drainage: Ensure the site has proper drainage to prevent water accumulation, which can damage plants and the structure.
2. Design and Dimensions
- Size: Determine the size based on your needs and available space. A typical size is around 8-12 feet wide and 12-20 feet long.
- Depth: Dig at least 6-8 feet deep to take full advantage of the earth’s insulation properties.
3. Excavation
- Digging the Pit: Excavate the area according to your design dimensions. Ensure the walls are straight and stable.
- Slope: Create a slight slope towards the entrance to facilitate drainage and easier access.
4. Wall and Floor Construction
- Walls: Use durable materials like concrete, brick, or treated wood for the walls. Insulate them with straw bales, foam boards, or other insulating materials.
- Floor: Install a gravel or sand floor to improve drainage. You can also add a layer of insulation below the flooring material.
5. Roofing
- Transparent Covering: Use clear plastic, polycarbonate panels, or glass to cover the greenhouse. This will allow maximum light penetration while retaining heat.
- Angle: Ensure the roof is angled towards the sun to maximize solar gain, typically around 30-45 degrees.
- Ventilation: Incorporate vents or windows that can be opened to regulate temperature and humidity.
6. Insulation
- Thermal Mass: Include materials like water barrels, rocks, or bricks inside the greenhouse to absorb heat during the day and release it at night.
- Additional Insulation: For colder climates, consider adding extra insulation to the roof and walls.
7. Planting and Maintenance
- Soil Preparation: Use high-quality, well-draining soil. Incorporate compost or organic matter to improve fertility.
- Watering: Install an efficient watering system, such as drip irrigation, to ensure consistent moisture levels.
- Temperature Monitoring: Use a thermometer to monitor and adjust the internal temperature as needed.
- Pest Control: Keep an eye out for pests and use organic methods to manage them, such as neem oil or beneficial insects.
Suitable Crops for Underground Greenhouses
- Leafy Greens: Lettuce, spinach, kale, and Swiss chard thrive in cooler temperatures.
- Root Vegetables: Carrots, radishes, and beets can grow well year-round.
- Herbs: Basil, parsley, cilantro, and mint are excellent choices.
- Fruit-bearing Plants: Tomatoes, peppers, and cucumbers can be grown with the help of trellises and stakes.
Tips for Success
- Lighting: Supplement with grow lights during shorter days to ensure plants receive enough light.
- Rotation: Practice crop rotation to maintain soil health and reduce pest buildup.
- Continuous Learning: Stay informed about best practices and new techniques for greenhouse gardening.
Conclusion
Building an underground greenhouse is an effective way to grow food year-round, providing a stable environment that conserves energy and resources. By following these steps and maintaining proper care, you can enjoy fresh, home-grown produce regardless of the season.