Last reviewed 1 Oct 2026 · Facts as of 1 Oct 2026 · 7 min read
Protected cultivation and the greenhouse effect
A greenhouse (polyhouse, glasshouse) is a framed structure covered with a transparent or translucent material in which the crop environment — temperature, humidity, light, CO₂, water and nutrients — is partly or fully controlled. It permits off-season and higher-value production, higher yield and quality, and protection from rain, wind, frost, birds and pests.
Greenhouse effect (in the structure): the cover transmits short-wave solar radiation, which is absorbed by the crop, floor and frame and re-emitted as long-wave (infrared) radiation; the cover blocks most of this long-wave radiation and restricts air exchange, so the inside air becomes warmer than outside. In Indian summers this heating must be removed (ventilation, cooling, shading); in cold northern winters it is useful.
Classification of greenhouses
1. By shape (cross-section)
| Type | Description | Remarks |
|---|---|---|
| Lean-to | Half a greenhouse attached to an existing building or wall (one slope) | Cheap, small; uneven light; home gardens |
| Even-span | Two equal roof slopes, symmetrical, gable roof | Common design; good light, ventilation, single or multi-span |
| Uneven-span | Two roof slopes of unequal length | Used on hill slopes |
| Ridge-and-furrow (gutter-connected, multi-span) | Several even-span units joined by a common gutter | Large commercial units; saves material and heat per m²; good for fan-pad; common for roses/gerbera |
| Quonset (hoop) | Semi-circular arched pipe frames covered with film | Low cost, simple, strong against wind |
| Gothic arch | Pointed arch roof | Sheds snow and water; strong without purlins |
| Saw-tooth | Staggered roofs with vertical vents | Natural ventilation in hot regions |
| Dome / geodesic | Triangulated spherical shell | Strong, minimum surface per volume, expensive |
2. By structural material
| Type | Remarks |
|---|---|
| Wood and bamboo | Low cost, short life, local material — bamboo-frame low-cost polyhouses in the North-East and rural India |
| GI (galvanised iron) pipe | Most common in India; durable, moderate cost; (rust/corrosion must be watched) |
| Mild steel (hot-dip galvanised) sections | Large commercial structures, strong |
| Aluminium | Light and corrosion-resistant, expensive — glasshouses |
| Concrete | Permanent installations |
3. By covering material
| Cover | Properties |
|---|---|
| Glass | High light transmission (about 85–90 %), long life (25+ years); heavy, expensive, breakable; commercial glasshouses in cold countries |
| Polyethylene (LDPE) film, UV-stabilised | Most used in India; 200 micron (about 800 gauge) UV-stabilised film, 3–5 years life; light transmission about 80–90 %; cheap and light; can be anti-drip, diffused, IR-blocking, or multi-layer |
| Polycarbonate (twin-wall) sheets | Strong, good insulation; 10–15 years; higher cost |
| FRP (fibre-glass reinforced plastic) sheets | Durable, diffuses light; yellows with age |
| Acrylic (PMMA) sheets | Excellent transmission, expensive |
| Shade nets (HDPE, 35–75 % shade) | Not a greenhouse covering for heat retention, but a "net house" for shade, insect-proofing and hail protection |
| Insect-proof net (40–50 mesh) | Side vents to keep out whitefly and thrips |
4. By level of technology and ventilation
| Class | Features | Typical use |
|---|---|---|
| Low-cost / low-tech | Bamboo or pipe frame, film, manual vents, no cooling | Nurseries, vegetables in cool/hill areas |
| Naturally ventilated polyhouse (NVPH) | Tall (about 5–7 m ridge height), large side and roof vents, insect nets; no fan | Most subsidised type in India; flowers, capsicum, tomato, cucumber |
| Medium-tech (fan-and-pad) | Fans and wet pad, sometimes with fogging/shade screens | Hot dry plains (cooling by evaporation) |
| High-tech (climate-controlled) | Computer controller, heating, cooling, CO₂ enrichment, artificial lighting, fertigation, thermal screens, recirculating | Cut flowers, seed production, tissue-culture hardening |
| Tunnels (low and walk-in) | Small hoops with film | Off-season vegetables, nursery protection |
(In India government horticulture missions (NHM, NHB, state horticulture departments) support greenhouses with subsidy at a fixed percentage of the cost norm per m² that depends on the type — check the current cost norms.)