Polytunnels: Maximising Your Garden’s Growing Season

Polytunnels, commonly known in the as polyhouses, hoop greenhouses, or grow tunnels, are an essential structure for anyone interested in horticulture and agriculture. These tunnels are usually constructed from sturdy steel frames and covered with a durable layer of polyethylene, which creates a controlled microclimate that can significantly extend the growing season for a variety of plants. Their design can vary from semi-circular to square or elongated shapes, catering to the specific needs of the plants being cultivated and the space available.

The utility of polytunnels extends beyond just season extension. They provide protection for plants from harsh weather conditions, pests, and diseases, while also facilitating the cultivation of fruits and vegetables that may otherwise be unsuitable for the local climate. This versatility has made them increasingly popular among home gardeners, small-scale farmers, and commercial growers alike.

In the South African context, for instance, the cost of these tunnel structures can vary greatly, reflecting the level of technology and sophistication they embody. Simple, low-cost structures might be available at an accessible price per square meter, while more advanced, automated tunnels with better ventilation systems can command a higher price. This variation in cost and design ensures that polytunnels can meet the needs of a wide variety of users, from those seeking basic season extension to those requiring high-end growing environments for more sensitive crops.

Understanding Polytunnels

A polytunnel, also known as a hoop house or high tunnel, functions similarly to a greenhouse, providing an enclosed environment for plant cultivation. It consists of a frame, typically made of steel, and is covered in polyethylene. The structure is predominantly semi-circular, square, or elongated in shape, creating a microclimate that is conducive to plant growth.


  • Shape and Size: Varied, with common dimensions ranging from 6ft to 14ft in width and 8ft to 20ft in length.
  • Materials: Frames can be metallic, plastic, or wooden, covered with durable polythene or equivalent materials.

Comparison with Greenhouses

  • Material: Unlike greenhouses, which are often glass-encased, polytunnels use a polythene covering.
  • Affordability: They are generally more cost-effective than traditional greenhouses.


  • Microclimates: They create microclimates that protect plants from the elements and pests.
  • Versatility: Suited for a variety of vegetation, they can accommodate different gardening needs.

Design Considerations

  • For polytunnels wider than 8 feet, it is advisable to design multiple paths to ensure easy access to planting beds.
  • Placement of the tunnel should take into account exposure to sunlight and shelter from the wind.

Polycarbonate tunnels serve as a practical solution for extended-season gardening, allowing horticulture enthusiasts to cultivate a broader range of plants throughout the year. They are revered for their utility in creating optimal growing conditions, making them a popular choice for those seeking an alternative to conventional gardening methods.

Design and Structure of Polytunnels

Polytunnels, versatile structures paramount in modern agriculture, have evolved to meet diverse horticultural demands. Their construction involves various frame types, coverings, dimensions, and additional features, carefully planned to enhance plant growth and extend growing seasons.

Types of Frames

Frames constitute the backbone of polytunnels, usually fashioned from steel, timber, or plastic materials. Steel frames offer corrosion resistance and durability, while timber presents a more natural look but may require more maintenance against decay. Plastic frames, lightweight and cost-effective, provide an alternative with easier installation.

Covering Materials

The most common material for covering polytunnels is polyethylene, known for its light penetration and UV protection. Alternatives like reinforced PE plastic and commercial-grade covers provide additional strength and longevity.

Size and Shape

Polytunnels vary in size, with widths starting at 16ft, stretching up to 30ft, and lengths that can extend from 66ft to well over 100ft. The shape is typically semi-circular, maximising volume and reducing wind resistance, though square and straight-walled designs are available for certain applications.

Access Points

Access is granted through various means, such as doors, roll-up doors, or dual-zip entrances. Modular designs allow for straightforward integration of additional access points as needed.

Ventilation Systems

To regulate temperature and humidity, polytunnels incorporate ventilation systems like roll-up side windows and insect nets, essential for climatic control within the growing environment.

Anchoring and Stability

Anchoring systems, using anchor plates, base rails, or a trench digging method, ensure the stability and strength of the structure against adverse weather. Skirting material may be added for extra weight and security.

Additional Features

Supplementary features such as insect screens, shading, internal partitioning, and irrigation systems can be integrated into the design of polytunnels to meet specific agricultural needs.

Building Instructions

Construction kits typically come with full instructions, clarifying the build process step by step. Erecting a polytunnel requires a methodical approach, with foundation tubes, corner bracing, and a ridge pole being key components.

Considerations for Site Selection

Selecting an appropriate site is critical, with priority given to areas with good drainage, level ground, and optimal sun exposure to ensure light penetration for enhanced plant growth.

Construction Tools and Materials

Essential tools include cement mixers for foundations, bricks or compost for raised beds, and various fittings for the assembly. The choice of tools and materials will impact the overall life of the polytunnel.

Maintenance and Repairs

Regular maintenance ensures longevity and performance. Common repairs might involve patching the polytunnel cover or replacing parts subject to wear, like the polyethylene sheet or frame joints.

Building a Polytunnel Kit

Polytunnel kits are designed for self-assembly, containing all required components, from frames to covers and anchors, simplifying the construction process for gardeners and commercial growers alike.

Polyculture and Crop Rotation

Implementing polyculture and crop rotation within polytunnels can optimise soil health, control pests, and improve overall yield.

Enhanced Plant Growth

The controlled conditions inside a polytunnel facilitate enhanced plant growth, allowing for more efficient use of resources like water and compost.

Extending the Growing Season

The use of polytunnels offers a significant advantage in extending the growing season. Plants can be cultivated year-round, with particular benefits for winter growing in temperate climates.

Agricultural Productivity

Compared to traditional outdoor farming, polytunnels can lead to increased agricultural productivity by providing a protected environment less susceptible to variable weather and pests.

Gardening and Lifestyle

For hobbyists and lifestyle gardeners, polytunnels offer a flexible and rewarding way to enjoy fresh produce, cultivate exotic plants, and engage with sustainable practices right in their back garden.

Frequently Asked Questions

In this section, one will find a compilation of common queries regarding polytunnels, addressing topics from their agricultural benefits to the specifics of material choices for cladding.

How do polytunnels benefit agricultural practices?

Polytunnels extend the growing season by providing a controlled environment, protecting plants from harsh weather, and promoting faster growth. They offer flexibility in cultivation, allowing a range of crops to thrive throughout the year.

What factors should one consider when selecting a polytunnel kit?

One should consider size, structure material, cover durability, and local weather conditions. The choice of a polytunnel kit should align with the intended use, such as the types of plants one wishes to grow and the available space.

What are the potential drawbacks of using polytunnels for cultivation?

Potential drawbacks include the initial cost of installation, the need for regular maintenance, and the risk of overheating on hot days. Ensuring proper ventilation and shading can mitigate some of these issues.

For what reasons might one choose a polytunnel over a traditional greenhouse?

Polytunnels are often more cost-effective than greenhouses and can be more easily extended or modified. They also allow for a higher degree of customisation to suit specific agricultural needs.

How do polytunnel prices vary in South Africa compared to the UK?

Polytunnel prices in South Africa may differ from those in the UK due to variations in material costs, availability, and demand. Currency differences and shipping fees also affect the final pricing for South African consumers when importing from the UK.

What materials are most effective for polytunnel cladding?

Polyethylene plastic, commonly referred to as polythene, is the most effective material for polytunnel cladding. It provides durability, light diffusion, and insulation while being cost-effective compared to alternatives like polycarbonate or glass.

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