Growing plants year-round, especially in colder or variable climates, can be a challenge. An underground greenhouse—also called a « walipini » or « pit greenhouse »—offers a sustainable, efficient solution. By utilizing the Earth’s natural insulation, these structures maintain stable temperatures, shielding plants from harsh weather and extending the growing season.
1. Benefits of an Underground Greenhouse
- Thermal Stability: The Earth’s insulating properties help maintain a consistent temperature a few feet below the surface.
- Weather Protection: Underground greenhouses are less exposed to wind, snow, and hail, reducing damage risks.
- Extended Growing Season: Stable conditions allow cultivation even in colder months.
- Sustainability: Minimal energy is required for heating, thanks to natural insulation.
2. Selecting the Ideal Location
- Sunlight: Choose a location with maximum sun exposure—south-facing in the Northern Hemisphere and north-facing in the Southern Hemisphere.
- Water Drainage: Ensure good drainage to prevent water pooling. Incorporate raised beds or gravel paths if needed.
- Accessibility: Opt for a spot you can easily reach year-round.
3. Building Your Underground Greenhouse
a. Excavation
- Depth: Dig 8–10 feet deep to utilize the Earth’s insulation. Depth may vary depending on your area’s frost line.
- Dimensions: Customize width and length to suit your needs. A common size is 10×20 feet.
b. Walls
- Construct walls with bricks, stones, or earthbags. For added durability, reinforce them with concrete.
- Insulate the northern wall with straw bales, foam panels, or other materials to retain heat.
c. Roofing
- Use UV-resistant greenhouse plastic, polycarbonate panels, or glass for the roof.
- Ensure the roof slopes to maximize sunlight and allow rain or snow runoff.
d. Flooring
- Gravel floors improve drainage. Alternatively, you can use concrete or leave a natural soil floor.
e. Ventilation
- Add vents or windows in the roof or high points to release hot air.
- Install doors at either end to improve airflow and accessibility.
4. Maintaining Your Underground Greenhouse
- Temperature & Humidity: Regularly monitor with a thermostat or hygrometer.
- Pest Control: Inspect for pests and use natural deterrents.
- Watering: Adjust watering schedules based on plant needs and humidity levels to avoid waterlogging.
5. Extra Tips for Success
- Water Barrels: Place barrels of water inside the greenhouse to absorb heat during the day and release it at night.
- Raised Beds: Use raised beds to prevent waterlogging and root rot.
- Reflective Surfaces: Install reflective materials on walls to enhance light distribution.
Conclusion
Building an underground greenhouse is a rewarding way to grow plants all year. Though it requires effort and investment upfront, the benefits of fresh, home-grown produce during colder months make it worthwhile. Regular maintenance and monitoring will ensure optimal growing conditions for your plants.