Polytunnel

[1] Polytunnels can be used to provide a higher temperature and/or humidity than that which is available in the environment but can also protect crops from intense heat, bright sunlight, winds, hailstones, and cold waves.

[2] Beyond season extension, polytunnels are also used to allow cold-hardy crops to overwinter in regions where their hardiness is not quite strong enough for them to survive outdoors.

Temperature increases of only 5 to 15 °C (9 to 27 °F) above outdoor ambient, coupled with protection from the drying effect of wind, are enough to let selected plant varieties grow slowly but healthily instead of dying.

The effect is to create a microclimate that simulates the temperatures of a location several hardiness zones closer to the equator (and protects from wind as well).

This does not increase the humidity levels in the poly house as the evaporated droplets are almost immediately ventilated to open air.

The recent Indo-Israel collaboration at Gharunda, near Karnal is an excellent example of Polyhouse farming taking place in a developing country.

Major themes of continuing development are (1) achieving the same results with lighter construction and less cost and (2) making hoophouses easily movable.