Brief description

A greenhouse is a structure with walls and a roof made mainly of transparent material, such as glass or plastic, in which plants requiring regulated climatic conditions are grown. It traps solar radiation to create a warmer environment than the surrounding area.

Use / Function

• Season extension: Allows planting earlier in spring and harvesting later in autumn.
• Climate control: Enables the cultivation of tropical or sensitive plants in cold regions.
• Protection: Shields crops from extreme weather (frost, heavy rain, wind) and some pests.
• Seed starting: Provides an ideal environment for germinating seeds before transplanting them outdoors.

Operating principle

The greenhouse operates on the “greenhouse effect”:

1. Solar Gain: Short-wave solar radiation passes through the transparent cover and is absorbed by plants and soil inside.
2. Thermal Emission: The absorbed energy is re-emitted as long-wave infrared radiation (heat).
3. Trapping: The glass or plastic cover is opaque to infrared radiation, preventing the heat from escaping by convection and radiation.
4. Thermal Mass: Objects inside (like stone walls or water barrels) store heat during the day and release it at night.

How to create it

1. Frame construction: Build a sturdy frame using Wood, bamboo, or metal.
2. Glazing: Cover the frame with transparent panels of Glass or sheets of Plastic.
3. Sealing: Ensure the structure is airtight to prevent heat loss, but include operable vents.
4. Foundation: Use Brick or Stone for a foundation to provide stability and thermal mass.
5. Technical Level: Intermediate. Requires knowledge of structural stability and glazing techniques.

Materials needed

• Transparent Cover: Glass (most durable) or Plastic film (cheaper/easier).
• Structure: Wood, Wire, or metal pipes.
• Thermal Mass: Dark-colored barrels filled with Water or a Stone floor.
• Tools: Saw, Hammer, and measuring tools.

Variants and improvements

• Cold Frame: A low-to-the-ground box with a glass lid, used for small-scale seed starting.
• Walipini (Underground Greenhouse): Built partially underground to utilize the earth’s constant temperature for insulation.
• Polytunnel: A large, tunnel-like structure covered in polyethylene plastic.
• Automated Greenhouse: Uses sensors and motors to control ventilation, irrigation, and heating.

Limits and risks

• Overheating: Without proper ventilation, temperatures can rise high enough to kill plants in a few hours.
• Humidity: Trapped moisture can lead to fungal diseases and rot.
• Structural Failure: Large glass panels are heavy and fragile; plastic can be torn by high winds.
• Maintenance: Glass requires regular cleaning to maintain light transmission.

Related Inventions

• Passive Ventilation: Essential for temperature control.
• Simple Irrigation: Often integrated for plant maintenance.