What Types of Polytunnel Plastic Cover Are Available for Gardens & Allotments?

When I started growing crops commercially I had a series of 120×18 ft and 120x14ft tunnels and the plastic choice was very limited. Plastic lifespan was usually 2 years with it rarely reaching three years. I was growing mainly salad and vegetable crops with the occasional flower crop. The plastic was UPV inhibited but the plastic weathered very badly and would split in areas where heat and abrasion high wear. Both these were common over the steel hoops and the sheet would rip in hight winds.

A garden polytunnel can user various Types of Polytunnel Plastic Cover

Saving a broken sheet in high winds was next to impossible as the surface area was 120 ft by the distance over the hoops … Pi r squared divided by two if you want to calculate it. That’ a huge windsock or sail when the wind is behind it. It’ll lift a human off the ground. Even a heavy one!

This mean there was also a potential problem when sheeting a tunnel. We had to drape the open sheet over the tunnel frame before securing it. The best way was to drag it over the metal frame at dawn when the sun was low and winds had died down. Then when the sun came up it would make the sheet pliable and we could stretch it on to the frame and secure it. Two people was considered the minimum for this though I have done it on my own a few times. It’s an interesting experience!

In case you are wondering what the difference between a polytunnel and a hoop house is, there really isn’t one. A hoop house, aka hoop greenhouse, poly hoop house, hoophouse etc is just the American term for what I call a polytunnel.

Polytunnel Purpose Defines The Type Of Plastic Cover

Depending on the polytunnels purpose we now have a choice of tunnel liners we can use. In most cases it will be a transparent type of plastic cover. But, in some cases an opaque or even blackout type is preferred. Think mushrooms being grown in the dark.

Polytunnels can be used for many purposes and one complaint is they are hard to cool down in hot weather. Follow the link for my advice on cooling polytunnels in hot weather.

Here’s my quick rundown on Types of Polytunnel Plastic Covers with the pros and cons. I’ve not mentioned plastic thickness as that is a whole new article for the future.

Large commercial polytunnel
  1. Clear Polyethylene Liners:
    • Purpose: Ideal for maximizing sunlight penetration and promoting robust plant growth.
    • Positives: Allows ample natural light, especially beneficial for light-loving plants. Cost-effective option.
    • Negatives: May lead to excessive heat buildup in warmer climates, potentially causing heat stress. Prone to UV degradation, resulting in a shorter lifespan.
    • Life Span: Typically 1 to 3 years.
  2. Diffused Polyethylene Liners:
    • Purpose: Scatters sunlight to ensure more uniform distribution, reducing hot spots and promoting even growth.
    • Positives: Addresses uneven lighting issues, providing consistent illumination. Suitable for a wide range of crops.
    • Negatives: May reduce the overall intensity of direct sunlight, potentially affecting the growth of light-sensitive crops.
    • Life Span: Around 3 to 5 years.
  3. Thermal Polyethylene Liners:
    • Purpose: Provides insulation to retain heat within the polytunnel, extending the growing season.
    • Positives: Enhances temperature control, creating a warmer environment. Suitable for cooler climates.
    • Negatives: May trap excessive heat in warmer weather, potentially leading to overheating. Vulnerable to punctures.
    • Life Span: Approximately 3 to 7 years.
  4. Shade Cloth Liners:
    • Purpose: Filters sunlight to provide shade and control temperature, preventing overheating of plants.
    • Positives: Protects plants from excessive heat. Reduces the risk of sunburn on sensitive plants.
    • Negatives: Reduced light levels can hinder the growth of sun-loving plants. Cloth may tear in strong winds.
    • Life Span: Typically 5 to 8 years.
  5. Reflective Liners:
    • Purpose: Enhances light distribution by reflecting sunlight onto plants.
    • Positives: Increases overall light exposure, promoting photosynthesis and growth. Useful for optimizing light in shaded areas.
    • Negatives: Reflection can cause hot spots if not managed properly. Material may lose reflectivity over time.
    • Life Span: Around 3 to 6 years.
  6. Blackout Polyethylene Liners:
    • Purpose: Blocks out light entirely for specific light control applications.
    • Positives: Provides complete darkness for light-sensitive processes. Useful for certain crops’ growth cycles.
    • Negatives: Complete darkness may affect natural processes like flowering and fruiting. Lack of UV exposure shortens the material’s lifespan.
    • Life Span: Typically 2 to 5 years.
  7. Ventilated Polyethylene Liners:
    • Purpose: Integrates ventilation for airflow control, preventing overheating.
    • Positives: Regulates temperature and humidity. Suitable for improving air circulation within the polytunnel.
    • Negatives: Ventilation mechanisms may require maintenance, and the material is susceptible to tearing.
    • Life Span: Approximately 4 to 7 years.
  8. Anti-Drip Polyethylene Liners:
    • Purpose: Reduces condensation within the polytunnel.
    • Positives: Effectively minimizes condensation. Helps prevent diseases associated with excess moisture.
    • Negatives: May not eliminate all condensation. Susceptible to punctures and tears.
    • Life Span: Typically 3 to 6 years.
  9. Anti-UV Polyethylene Liners:
    • Purpose: Blocks harmful UV rays, protecting plants from UV damage.
    • Positives: Shields plants from UV radiation, reducing the risk of sun damage. Offers enhanced plant protection.
    • Negatives: May reduce overall light levels, impacting plant growth. Vulnerable to tearing.
    • Life Span: Around 4 to 8 years.
  10. Insect-Proof Polyethylene Liners:
    • Purpose: Acts as a barrier to insects and pests, minimizing infestations.
    • Positives: Provides a protective shield against pests. Reduces the need for chemical interventions.
    • Negatives: May restrict airflow within the polytunnel. Periodic cleaning may be necessary.
    • Life Span: Typically 3 to 6 years.
  11. Construction Plastic: Plastic manufactured of damp proofing or as construction membranes aren’t ideal. They aren’t designed to cover crops and are not cost effective.

As amateur growers and gardeners we need to weigh up the positives and negatives of each type and select a polytunnel liner based on our specific needs, plant types, and local climate conditions.

Best Vegetable Plants To Grow In the Shade; Growing in polytunnels
Best Vegetable Plants To Grow In the Shade; Growing in polytunnels
Tag: Types of Polytunnel Plastic Cover

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