Polytunnels

A polytunnel is a tunnel-like structure that first appeared in the 1960s. It is framed with steel and is generally made of crop bars, base rails, and a plastic polythene cover. Although primarily used by gardeners and commercial growers for growing vegetables, fruits, and flowers, they can also be used to house livestock, or for storage. They can range from 6 to 30ft in length and come in various sizes, catering to small- and large-scale operations.

Most polytunnels are semi-circular in shape, but some also have straight walls. In essence, they are similar to greenhouses, but polytunnels are much more affordable. The main purpose of a polytunnel is to create a microclimate that provides higher temperatures and humidity to grow vegetable and fruit plants all year around.

What to Look for when Purchasing a Polytunnel

Polytunnels are available in various sizes. The hoop diameter of the tunnel is relevant to the overall strength of the structure. A thicker hoop will mean the overall structure is stronger. Before purchasing a polytunnel, determine a suitable size for your area. The polytunnel should be strong with a durable plastic sheeting cover, resistant to ultraviolet rays, and has sealable doors.

Ventilation is extremely important and should always be considered in polytunnel construction. During the hottest months of the year, you will need a temperature-controlled fan or a polytunnel that can be rolled up around the sides. Opening large sealable doors and vents on either side of the polytunnel should provide good airflow and prevent plants from drying out.

Durability is also important in polytunnels. The metal structure can last between 15 to 20 years, but the plastic covers need to be replaced every few years. The placement of your polytunnel will also determine how long the cover will last, like placing it where it won’t be greatly affected by strong winds. In extreme wind conditions, you can also space the polytunnel hoops closer together for extra stability and add brace bars to increase its strength and durability.

Polytunnel Benefits

Polytunnels have various benefits. Firstly, crops can grow quickly and possibly larger depending on your harvesting method. They are an excellent form of crop protection as they protect plants from wind, rain, snow, direct sunlight, cold, and heat. Further enabling growers to plant during all seasons. Since polytunnels absorb the sun, they can achieve productive germination and appropriate growing temperatures. Polytunnels are available in a wide range of sizes and are less expensive than glass or traditional greenhouses.

Another major benefit is that they are not permanent structures, meaning they can easily be taken down or moved. This also means that if the frame is not attached to the ground properly, it can be blown away by strong winds.

Growing in a Polytunnel

All types of flowers, fruits, herbs, trees, and vegetable plants can be grown in a polytunnel. Almost 80% of all soft fruits on the market are grown in polytunnels. Some common fruits include strawberries, raspberries, and melons, and some common vegetables include tomatoes, cucumbers, and artichokes. For a polytunnel to function effectively it needs flat, even ground, access to a water supply, and sunlight. A structure facing north to south is ideal for equal amounts of shade on either side to reduce overheating in the summer and minimize direct heat from the sun. An east-west structure in a hot climate is not ideal in the summer as it means the crops in the north bed will be in the shade while the crops in the middle grow tall.

Types of Polythene Plastic

There are various options of polythene plastic, including more expensive thermic or anti-condensation polyethene’s. It is recommended to begin with the standard, light-diffusing polythene which admits around 89% of daylight. Using a horticultural grade polythene will ensure you have a UV stabilizer, preventing it from becoming brittle. The polythene should be buried all around the trenches of the polytunnel. This will protect it from animals such as rabbits, slugs, cats, and dogs and protect it from weeds.

Pest Control in Polytunnels

Polytunnels offer good protection against pests, but as a preventative measure, you should keep the polytunnel well ventilated. This will help maintain good temperatures and avoid too much humidity which can enable the establishment of various pests and diseases.

What are High Tunnels?

While often equated with traditional greenhouses, high tunnels are designed to be a more versatile, larger, and taller polytunnel. They are light, mobile, flexible, and versatile. They can provide a growing area for plants while also accommodating tractors, tillers, and other farm machinery. Though originally designed as a space to bring large machines, they have been newly designed to provide the same benefits as other polytunnels. They have a single layer of poly covering that can easily be removed to give crops exposure to the outdoors. Since they do not require a traditional foundation, they can be installed very easily and quickly, and like traditional polytunnels they can be moved.

What are Hoop Houses?

Though polytunnels are often called hoop houses, they are not the exact same. Their name originates from a cold frame, which is a transparent outdoor frame that protects plants from the cold weather and uses solar energy. Hoop houses are simply a smaller sized tunnel designed for small-scale farms that extract the same benefits as other polytunnels or high tunnels. Just like polytunnels, they do not require a durable foundation, but they are a good solution for small to medium sized operations looking to grow flowers, vegetables, fruits, and herbs while also providing protection from light winds, sun, and rain.