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A greenhouse tunnels is a type of greenhouse. It is known by a variety of names, but they all consist of a metal frame with a plastic exterior used to extend a crop’s growing season. Greenhouse tunnels come in two sizes, a low tunnel and a high tunnel, yet both look the same and function the same way. .
Cold frame, hoop house and French tunnel are all alternative names for the greenhouse tunnel, yet no matter the title they are all typically designed in the same fashion. They are shaped like a half cylinder and made with an open metal frame that is covered with clear plastic. This frame is then placed over plants or crops that are in need of extra warmth or protection.
There are two different types of greenhouse hoops, the tall hoop and the low hoop. Both are designed in much the same fashion, but the low hoop is close to the ground, often times not rising above 2 to 3 feet (.6 to .9 meters). High hoops are at least large enough for an individual to stand up in, and are able to grow tall crops.
Greenhouse tunnels work because their clear plastic exterior traps in the sun’s heat and keeps its interior warmer than the outdoor temperature. They are also able to protect plants from mild freezes and high winds or heavy rains. In hot climates the plastic exterior can be pulled back to ventilate the space, and if strong sun rays threaten to scorch the plants then the plastic covering can be replaced with a cloth covering that provides shade.
Because of these benefits, the greenhouse tunnel is able to significantly extend the growing season of many crops. Seeds can be planted outdoors in the tunnel when it would still be too cold to plant them outdoors otherwise. Crops can survive in the greenhouse tunnel longer into the end of the season than they could outdoors as the weather becomes colder.
Crops grown within the greenhouse tunnel can range from fruits and vegetables to flowers. Usually plants in a tunnel are planted directly into the ground as they would be if planted in a garden or field, rather than in pots or containers. Plants grown in a tunnel must be regularly irrigated as rainwater does not penetrate the exterior.
There are also a number of disadvantages to greenhouse tunnels. Many high tunnels are immobile or very difficult to move. This means there is limited opportunity for crops to be rotated or for the ground to lay fallow unless the gardener or farmer happens to own a number of greenhouse tunnels. Lack of plant rotation raises the chance of disease developing in the soil and also raises the risk for the soil under the tunnel becoming exhausted. Since the covering is made of plastic, tunnels can be damaged by heavy winds.