Polyhouse Farming Guide (2024) – Advantages, Cost & Profit

Polyhouse farming in India is gaining fast popularity as farmers can make huge profit from a small piece of land. It is considered as the future of farming. Here is an overview of polyhouse technology, how to make a polyhouse and how to manage it.

Polyhouse cultivation is a relatively new concept under which crops are grown in a controlled environment. In this system crop duration, harvesting time, yield, crop quality, etc. are enhanced by regulating temperature, humidity, sunlight, wind, rain, etc. factors. Disease, pests and weeds are reduced in protected cultivation. The quality of the produce is also superior due to low pollution, pesticides, pests, etc. external factors.

The main objective of polyhouse cultivation is achieving year-round, off-season high value crops with higher yield per unit area and more profit per unit resources like land, water, pesticide, etc.

What is a Polyhouse?

A polyhouse is a type of protected cultivation structure that is covered with UV stabilised polythene to create an artificial climate inside the structure and help grow crops under optimum conditions.

Principle of a Polyhouse

Polyhouse is only a type of protected cultivation structure among many. The main principle of a polyhouse is to capture the greenhouse gas inside the structure. As greenhouse or polyhouse is made of transparent glass or polythene cover where interiors grow warmer when exposed to sunlight as the cover blocks the greenhouse gas to exit. Therefore, while it may be cold outside the temperature is survival friendly and warm for the plants growing inside. Some greenhouses using high-end technology have installed equipment like heating and cooling system, lighting, screening installations and even computerized facilities to provide optimal growth conditions for the plants. This is done especially to reduce the risks of crop loss in greenhouse cultivation.

Difference Between Polyhouse and Greenhouse

All types of protected cultivation structure is commonly known as greenhouse for their ability to create a greenhouse effect artificially by controlling the interior environment. A polyhouse is a type of greenhouse structure where UV stabilised polyethylene is used as the cover material.

A. Greenhouse: A greenhouse is made of some kind of transparent material to create a microclimate inside the house. Different materials like glass, wood, polyethylene etc. are used as greenhouse cover to create the microclimate. When a greenhouse is made with glass cover it is referend as glass greenhouse or glass house.

B. Polyhouse: A polyhouse is one type of greenhouse where polyethylene is used as the cover. In India, polyhouse farming is the most popular greenhouse technology for it’s low cost of construction. Lath house is another greenhouse technology where wood is used as the cover.

Poly house is economical compared to glass house or glass greenhouse but the later is more durable than polyhouse and is more suitable in cold places where it snows.

Best Crops for Polyhouse Farming

Many crops can be grown in a polyhouse but farmers should calculate the ROI (Return on Investment) when selecting a crops for growing in a polyhouse as the construction cost of a polyhouse is quite high. Cut flowers, high value vegetables, some fruits and disease free planting materials are best suited for polyhouse/ greenhouse cultivation.

Crops Grown Under Polyhouse Cultivation

Types of Greenhouse

There are different types of greenhouses according to cost, shape, structure type, construction material, glazing type and environmental control. Farmers should choose a greenhouse type as per their particular needs and investment capacity.

1. Greenhouse Types Based on Cost and Suitability

a. Low Cost Greenhouse/ Bamboo Greenhouse

As the name suggests, low cost polyhouse is constructed using locally available materials like bamboo. The light intensity is controlled using shade nets. UV stabilised polyethylene film is used for covering. Simple techniques like side wall opening or closing is used for controlling temperature during summer and winter. They serve as good shelters for rain. This type of structure does not have high technology facilities and is mainly used in places with cold climatic conditions. The cost for constructing this type of polyhouse varies between ₹ 300- 500 per square meter. Marginal farmers with small land holdings can take the benefits of greenhouse farming using low cost bamboo polyhouse.

b. Semi-Automatic Greenhouse

Some greenhouses are partially controlled with minimum investment conditions. Pipes made of galvanized iron are used for the construction and the canopy is held together with the help of screws. It is lodged firmly in the ground to withstand the wind. There are exhaust fans with thermostat system to control the temperature. There are also cooling pads and arrangements for misting to maintain humidity levels. Such structures are suitable for areas with dry and composite climate. The cost for constructing this type of greenhouse varies between ₹ 800- 1100 per square meter. This type of polyhouse is the most popular greenhouse structure farming in India.

c. High-End Greenhouse

These structures are installed with polyhouse automation devices to control temperature moisture, humidity and other environmental parameters. The cost for constructing this type of greenhouse is approximately ₹ 2000-3500 per square meter. This type of polyhouse is used for very high value crops and hydroponics in commercial greenhouse farming.

2. Greenhouse Based on Structure Types

There are 3 types of greenhouses in this category:

1. Quonset type
2. Curved roof type
3. Gable roof type
4. Sawtooth type

The main category of classification is based on the type of material used for support such as PVC frames, steel supports, etc.

3. Greenhouse Based on Glazing

This classification is based on the type of material used for covering the structure. They maybe:

1. Fiberglass reinforced plastic glazing
2. Glass glazing
3. Plastic film

The material used for fiberglass reinforced plastic glazing can be plain sheet or corrugated sheet. The plastic film used is UV stabilized low density polyethylene. This is the most popular covering material for polyhouse farming in India.

4. Polyhouse Based on Number of Spans

1. Single span
2. Ridge and furrow

5. Polyhouse Based on Environmental Control

a. Naturally Ventilated Polyhouse

The structures have good ventilation systems to prevent basic weather and natural damage. However, they do not have any additional provisions to control the environment in polyhouse farming.

b. Environmentally Controlled Polyhouse

This type of greenhouse is basically constructed for off-season production. Factors like light, temperature, carbon dioxide levels, humidity, etc. are controlled.

Polyhouse Design

A polyhouse is designed based on environmental conditions of the site and those required for plant growth in polyhouse farming. Taking into consideration the Indian climatic conditions, multi-span, Quonset type greenhouse is the most preferred. It is economical and can be easily constructed. For naturally ventilated greenhouses low density polyethylene films stabilized under UV is used. Some people also use films having a thickness of 200 microns. Screws and nails are not used since the films may get torn off. Instead, they are fastened using T-lock or L-lock. While designing the greenhouse it should be remembered that the structure must bear different types of loads like:

• Dead Load- It is the weight of all the equipment fixed on the frame such as water pipes, service equipment, heating and cooling systems, cladding and the weight of permanent constructions.
• Live Load- A greenhouse is devised to carry a maximum weight of 15 Kg per square meter. In addition, the roof members must be capable of supporting shelves, hanging baskets, people, etc.
• Wind Load- The structure must have the capacity to withstand 50Kg per square meter of wind pressure.
• Snow Load- This is considered in areas having snowfall. In case of snow fall, the structure must be able to bear all the different loads in addition to the snow load.

Components of a Polyhouse

A polyhouse is made of multiple components. The different components of a polyhouse are

• Roof- It is the transparent overhead cover of the greenhouse.
• Gable- The wall of the greenhouse is called gable which is transparent.
• Gutters- Gutters collect and drain out the snow and rain water that is gathered between the spans.
• Column- It is vertical structure that carries the greenhouse.
• Ridge- It is the horizontal section on top of the roof.
• Bracings- Bracings are erected to support the structure against wind.
• Arches- They are the structures that support the covering materials.
• Foundation Pipe- Foundation pipes connect the structure to the ground.

Orientation of Polyhouse

The orientation of a polyhouse depends on the shadow movement, shading effect, type of temperature control, wind direction and latitude. In case of other polyhouses nearby, the orientation should be such that its shadow does not fall on other greenhouses. For this purpose, they are oriented in an East to West direction.

Dimensions

To decide the dimensions, a host of factors like size of the polyhouse, wind effects, height, spacing between the greenhouses and its structural design must be considered.

• Wind effects: The length of the polyhouse must be perpendicular to the direction of the wind. In case of fan and pad arrangement, the direction of natural wind must be the same as that of the air blown by the fan.
• Size of polyhouse: A bigger polyhouse would have more temperature build-up especially if there is no proper ventilation. In case of naturally ventilated greenhouse, the length must not exceed 60m.
• Spacing between polyhouses: There should be a distance of 10-15m between two polyhouses. This is to avoid shadow from falling on each other. In addition, the exhaust from one polyhouse greenhouse must not enter the other polyhouse.
• Height: A 50m X 50m polyhouse can attain a maximum height of 5m. A taller polyhouse would have larger wind load for the glazing and structure.
• Structural design: The structure of the polyhouse must be able to bear all the different loads. Hence, the column, foundation and truss must be designed accordingly. They must follow the guidelines specified by the National Greenhouse Manufacturers Association (NGMA of US) standards.

Cladding Materials for Greenhouse Farming

Cladding is nothing but covering of the greenhouse. There are different materials used for cladding a greenhouse such as polycarbonate, polyethylene, fiberglass, UV resistant polyethylene films and Tedlar coated fiberglass. Double strength glass and polycarbonate have a durability of 50 years and require very low maintenance. Polyethylene films in polyhouse require high amount of maintenance but are durable for only 3-5 years. Fiberglass is durable for seven years while Tedlar coated fiberglass can sustain upto 15 years.

Containers for Greenhouse Farming

Different types of containers are used in a greenhouse for different purposes like growing plants under controlled climatic conditions, raising the seedlings, growing plants for hybrid seed production and for growing ornamental plants in pots. Using containers increase capacity of the production while reducing the crop time in polyhouse farming. Containers ensure uniform growth of plants and minimum transplantation shock. In addition, it eases monitoring of plants and plant nutrition.

Here is a table with different types of containers used in polyhouse farming along with their advantages and disadvantages:

Watering System in Polyhouse Farming

Drip irrigation is the best technique for watering the plants owing to the small root system. It must be ensured that the water is dispersed at the root area only and that it does not fall on the leaves or flowers. Falling on leaves and flowers may lead to infection, disease spread and even scorching. Water is forced out through the nozzles under very high pressure through the micro-sprinklers. These sprinklers are arranged at a height of 1 foot above ground level so as to ensure that water is dispersed at the basal part of the plants.

Maintenance of Greenhouse

The chief expense of greenhouse is the maintenance of the transparent films. The biofilm on the walls and roof must be washed periodically since dust settles on them reducing the light transmittance. The greenhouse must be solarized annually. Solarization is done by mulching and the interiors are fumigated. Biological control of insects or installation of insect traps is mandatory in greenhouse agriculture. The pipes and sprinklers of the irrigation system must be cleaned periodically so as to prevent accumulation of microbes that may lead to infection in plants. If following organic farming then extra care should be taken.

Problems in Greenhouse Farming

Since plants are being cultivated under controlled climatic conditions in a greenhouse, it has its own share of problems too. One of the chief problems is ensuring nutrient availability and protecting the plants from deficiency of various minerals like boron, nitrogen, phosphorous, calcium, iron and potassium. Similarly, plants may also suffer from excess of nutrients. Constant monitoring and soil testing is necessary to ensure that the plants get adequate amount of nutrition and grow properly.

Site Selection for Greenhouse Construction

In its early years, the aim of a greenhouse was to grow species that require heat in colder regions. It was easier to control climatic factors like temperature and moisture level inside a greenhouse and protect the plants from the harsh external cold winds. In India, the following points are to be considered for selecting the place to set up a poly greenhouse:

Water Logging

The site must be a well-drained area and not a place that has water logging issues. Water logging can cause potential harm to the crops especially in areas with heavy rainfall and floods.

Pollution

The greenhouse must not be built near industrial units. This is to protect the crops from possible pollution effects.

Accessibility

Although it should not be placed very near the roads, yet, they must be easily accessible through various modes of transport.

Conclusion

Construction of a polyhouse may seem a costly affair but one can make a huge profit from polyhouse cultivation compared to traditional farming. Horticultural departments and state governments provide subsidies to encourage polyhouse farming among farmers.