Key Concept: This unit deals with "Protected Cultivation" – the technique of growing plants in a controlled environment to protect them from harsh weather and pests, allowing for year-round, high-quality production.
Green house
A greenhouse is a general term for a structure with walls and a roof made chiefly of transparent material (like glass or plastic) in which plants requiring regulated climatic conditions are grown.
Technology
The core technology of a greenhouse is based on the "greenhouse effect."
Light Transmission: The transparent covering (glass or plastic) allows short-wave solar radiation (sunlight) to pass through.
Heat Trapping: The sunlight is absorbed by the plants and soil, which then radiate the energy back as long-wave thermal radiation (heat).
Containment: The covering is opaque to this long-wave radiation, trapping the heat inside and raising the internal temperature.
Modern greenhouses use advanced technology for full climate control:
Climate Control: Heaters, cooling systems (e.g., fan-and-pad evaporative coolers), and ventilation systems (roof/side vents).
Automation: Sensors and computers automatically control temperature, humidity, and light levels.
Irrigation: Automated systems like drip irrigation or misting systems (foggers).
Lighting: Artificial "grow lights" to supplement natural sunlight, especially in winter.
[Diagram: Showing short-wave radiation entering a greenhouse and long-wave (heat) radiation being trapped inside]
Management
Managing a greenhouse is a technical job requiring daily monitoring.
Temperature Control: Preventing overheating (the biggest challenge) by using ventilation and shade nets. Preventing excessive cold in winter with heaters.
Humidity Control: High humidity can cause fungal diseases. Ventilation and fogging systems are used to manage it.
Pest & Disease Control: The enclosed environment is ideal for pests. Management involves strict sanitation (keeping it clean) and often using biological controls (e.g., releasing "good" predator insects).
Carbon Dioxide (CO2) Management: In high-tech greenhouses, CO2 levels are artificially increased (CO2 enrichment) to boost the rate of photosynthesis and increase plant growth.
Advantages
Year-Round Production: Allows for "off-season" cultivation of vegetables and flowers, which fetch a higher market price.
Protection from Weather: Protects high-value crops from heavy rain, hail, wind, and frost.
Higher Yield & Quality: The "ideal" growing environment results in faster growth, higher yields, and better-quality (blemish-free) produce.
Water Conservation: In a controlled system like drip irrigation, water use is far more efficient than in an open field.
Pest & Disease Control: The physical barrier reduces pest entry, leading to lower pesticide use.
Acclimatization: Used to "harden off" (acclimatize) young, delicate plants grown from tissue culture before moving them outdoors.
Polyhouse
Polyhouse: A specific type of greenhouse where the transparent covering material is polythene (polyethylene) film (plastic sheet).
This is the most common and cost-effective type of greenhouse in India. The structure itself is usually a simple frame made of GI pipes or bamboo.
Advantages:
Much cheaper to build than a glass house.
Lightweight and easy to construct.
Plastic films are often treated with UV stabilizers (to prevent breakdown) and anti-drip coatings.
Disadvantages:
Plastic film degrades over time (3-5 years) and needs to be replaced.
Less durable than glass; can be torn by high winds.
Glass house
Glass house: A specific type of greenhouse where the covering material is glass.
These are the "classic" greenhouses, often seen in botanical gardens and research institutes.
Advantages:
Extremely durable and long-lasting (glass doesn't degrade).
Excellent light transmission.
High aesthetic appeal.
Disadvantages:
Very expensive to build.
Requires a strong, heavy frame (aluminum or steel).
Glass is brittle and can be broken by hail or impact.
Shed house
A "shed house" is not a standard horticultural term, but it likely refers to a simple structure used for nursery operations that are *not* plant growth.
Probable Use: A "potting shed."
Function: A simple, roofed structure (often with 3 walls) used for:
Storing tools, pots, fertilizers, and equipment.
Providing a dry, shaded area for nursery workers to perform tasks like potting, mixing soil, and sowing seeds.
Net house
Net house (or Shade house): A structure covered with agro-shade nets (woven plastic fabric) instead of a solid film.
This structure does not trap heat. Its primary purpose is not to heat, but to protect.
Technology: The nets come in different "shade percentages" (e.g., 30%, 50%, 75%) and colors (green, black, white).
Shade Percentage: A 50% net blocks 50% of the sunlight.
Color: Green is common for general growth; white reflects heat.
Function:
Reduces Light Intensity: Used for growing shade-loving plants (e.g., ferns, anthuriums, orchids) that would burn in full sun.
Reduces Temperature: By blocking sunlight, it creates a cooler environment.
Physical Protection: Protects crops from heavy rain, hail, and strong winds.
Pest Control: Fine "insect nets" can be used to physically block insects, reducing pesticide use.
Use: Very common in nurseries for hardening off young plants and growing delicate ornamentals.