Protected cultivation:- Protected cultivation is cultivating plants inside a structure that protects plants from wind, precipitation, excessive radiations, temperature extremes, insects, and diseases.it is also vital important to create an ideal microclimate around the plants

The main aim of protected cultivation

• To increase the productivity of the crop/ unit area
• To year-round cultivation
• To improve cultivation
• To control various environmental factors

Different protective structures (Green House) for ornamentals

1) Glass House:- The earliest type of greenhouse. Glass houses have a long life span, are the least affected by weathering, are non-combustible, resistant to VU radiation and air pollutants. Glass houses are of different types. Glass requires regular cleaning to maintain maximum light transmission.

2) Plastic Houses:- Modern plastics provided an alternative to traditional glass for covering the greenhouse. Plastic glazing includes rigid plastic structured panels like fiberglass reinforced polyester (FRP), polycarbonate (PC), acrylic, polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and ethylene-vinyl acetate copolymer. These materials are used in single double and even triple layers to cover the greenhouse. Judicious use of plastic helps to reduce ill effects on the environment.

3) Shade Net House:- these are hand-woven nets with different light transmission capacities; shading is often the most suitable procedure to overcome high humidity and temperature or low humidity in the greenhouse or outdoors. Light waves passing through the nets are affected by shade created by the shape and weave of net threads and by the net quality and material surface.

Type of Green House Based on Shape

1) Lean-to design- This is used when a greenhouse is a place against the side of an existing building. This design makes use of sunlight and minimizes the requirement for roof support. In actual practice, the lean-to type is the cheapest to build.

2) Even span Greenhouse (Gable Type):– In these two roof slopes are equal width. It is easy to structure.

3) Uneven span Greenhouse:- This has roofs of unequal width which make the structure adaptable to the side of a hill. This is rarely used now because they are not adaptable for automation.

4) Ridge and furrow type (Multispan):-Ridge and furrow refer to two or more greenhouses connected to one another the length of the greenhouse. The sidewall is eliminated since it has a single interior. Consolidation of interior space decreases the cost of automation, generally used for the production of carnation, rose, pot mums, or crops that can tolerate comparable environmental conditions.

5) Gothic (Pointed roof):- It is highly efficient have a pleasant appearance and withstands wind due to its curved superstructure.

6) Quonset (Semicircular Type):- The roof of this type of greenhouse will be semi-round in shape the roof covering may be polythene, fiberglass, or polycarbonate panels.

7) Gome (ground to ground type):- These can be constructed by using steel tubing and with either single or double polythene cover. The major disadvantage is that we cannot grow tall plants on the side, thereby losing some valuable greenhouse space.

Construction of a greenhouse

Site Selection:-

The site selected should have a proper drainage facility. A greenhouse needs a dependable source of good quality water and electricity. The greenhouse should be located away from the buildings and trees to avoid obstruction to sunlight.

Orientation:-

In the single-span greenhouse, the orientation should be in any direction. But multi-span greenhouse should be oriented in North-South direction only to avoid shading effect. A free-standing greenhouse that had its long axis perpendicular to the wind direction was relatively free from wind damages.

Fabrication of frame:-

A poly house of 300-500 m² area would be desirable for growing commercial flowers. To reduce the cost of construction, depending on the size and durability of the structure use of mild steel or GI pipes as the structural frame is desirable. This is less expensive than aluminum angles. The length, width, and height of the structure could be varied depending on location and intended purpose.

Covering/ cladding/ glazing material:-

Materials should be selected according to the type of greenhouse, the climate of the place, crop requirement, and economics. In India, polyethylene film, acrylic, and shade nets are commonly used.