Omar Khalid
Low tunnels are temporary structures that are used to extend the growing season for crops and protect them from the elements. They are typically made from wire or plastic hoops that are covered with a layer of plastic sheeting or greenhouse plastic. The type of plastic used for low tunnels is important, as it needs to be durable enough to withstand high winds and provide adequate protection from the cold for the crops. While some people use regular builder's plastic for their low tunnels, others opt for thicker, more durable plastic such as polyolefin or construction-grade plastic that can last for several years.
| Characteristics | Values |
|---|---|
| Plastic type | Polyethylene, Polyolefin, Construction-grade plastic, Premium plastic |
| Plastic thickness | 0.8 mil, 4 mil, 6 mil |
| Plastic properties | Tear-resistant, Ultra high-quality, Anti-drip, Anti-aging, Anti-fog coating, Hard to tear, High tensile strength |
| Plastic use | Covering for low tunnels, Greenhouse plastic, Row cover |
| Tunnel structure | Temporary, approximately 4 feet tall and 3 to 6 feet wide, Supported by wire hoops or plastic/metal pipes |
| Tunnel use | Protection from frost, cold injury, wind, insects, high temperatures, snow |
| Tunnel ventilation | Plastic should be lifted on warmer, sunny days to allow ventilation and prevent overheating |
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Polyethylene plastic
Polyethylene, also known as PE, is a versatile plastic that can be modified to exhibit specific physical properties while retaining its thermal and chemical resistances. For tunnel lining applications, very low-density polyethylene (VLDPE) is often used. VLDPE has a highly branched molecular structure with many side chains, resulting in low density and crystallinity. This gives VLDPE-based products increased flexibility and lightness compared to other materials of the same thickness.
The flexibility and low density of VLDPE make it ideal for use in low tunnels as it can be easily draped over supporting structures without adding excessive weight. Additionally, its thermal properties help regulate the temperature inside the tunnel, providing frost protection at night and solar warming during the day.
Compared to other plastics, polyethylene is generally more affordable and accessible. However, it is important to note that polyethylene plastic can cause moisture buildup inside the tunnel, so it should be used sparingly and only when necessary. To mitigate this issue, low tunnel clips can be used to secure the sides of the plastic to the hoops, allowing for ventilation and preventing overheating.
Overall, polyethylene plastic is a cost-effective and functional choice for creating low tunnels, providing crops with a warmer and more protected environment while also being flexible, lightweight, and easy to work with.
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Plastic thickness
The 6-mil-thick plastic is a 5-layer plastic film that provides UV stabilization to resist degradation from sunlight. It also comes with an anti-drip, anti-aging, and anti-fog coating, further enhancing its durability. This thickness is suitable for creating poly low tunnels using Kwik Hoops or similar structures, providing a cost-effective solution for farmers and growers.
On the other hand, thinner plastics, such as 0.8-mil thickness, are also available for low tunnels. This thickness is designed for use over small, vulnerable crops at the beginning of the season. It provides moderate frost protection and shields plants from wind and environmental hazards. The thinner plastic allows for solar warming during the day and a more protected environment at night.
It's important to consider the trade-offs between thicker and thinner plastics. While thicker plastics offer greater durability and tear resistance, they may be more expensive and might not be necessary for all applications. Thinner plastics are more affordable and lightweight, making them easier to install and remove. However, they may not provide the same level of protection or durability as thicker plastics.
Ultimately, the decision on plastic thickness depends on the specific requirements of the crops and the environmental conditions they need to withstand. Both thicker and thinner plastics have their advantages, and choosing the right thickness can ensure optimal crop growth and protection.
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Ventilation
Low tunnels are temporary structures that can be used to extend the growing season and protect crops from the elements. They are typically made from wire or plastic hoops that support a plastic cover.
When using plastic for low tunnels, it is important to consider ventilation. On warmer, sunny days, the plastic cover of a low tunnel will need to be lifted to allow ventilation and prevent plants from becoming overheated. This can be done by securing the lifted sides of the plastic to the hoops using low tunnel clips.
It is important to note that plastic can cause moisture build-up inside the tunnel, so it should only be used as needed. On sunny days with ambient temperatures above 55°F (13°C), the plastic cover can be removed for cool-season crops. However, it may need to be replaced in the evenings and overnight when temperatures drop below 32°F (0°C).
To improve ventilation, some gardeners choose to cut holes in the plastic and attach screening. This allows for air circulation while still providing protection from pests and other elements.
In addition to ventilation, it is important to consider the type and thickness of plastic used for low tunnels. Clear plastic is often preferred as it allows more light to reach the crops. The thickness of the plastic will depend on the expected wind and weather conditions, with thicker plastic providing more durability and tear resistance. Polyolefin plastic, for example, has higher tensile strength and heat retention than cheaper polyethylene plastics.
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Clips and clamps
Garden clips or snap clamps are specifically designed for this purpose and can be purchased from garden and greenhouse supply stores. These plastic clips are easy to work with and provide a convenient way to attach the plastic cover to the pipes or hoops of the low tunnel. They are available at various retailers, including Johnny's and other garden specialty stores.
For those who prefer a DIY approach, it is possible to make your own clips from plastic pipe. However, it is important to note that pre-made clips are generally more user-friendly, especially if you need to frequently remove and reattach the cover.
When using low tunnels, it is crucial to consider the potential for moisture buildup inside the structure due to the plastic cover. Therefore, it is recommended to only use the cover as needed and employ ventilation techniques, such as lifting the sides and securing them with low tunnel clips, to maintain optimal conditions for the plants.
Additionally, clips can be used strategically to address wind-related issues. One effective method is to alternate a cord across from one arch to the next, using a ridge pole to hold the cord in place. This technique reduces the reliance on numerous clips while still providing stability against high winds.
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Plastic durability
When choosing plastic for low tunnels, it is important to consider the durability of the plastic. Low tunnels are temporary structures designed to cover and protect a single row of plants from environmental factors such as rain, wind, and frost. They are constructed using long sheets of plastic draped over semi-permanent structures or hoops.
The durability of the plastic used for low tunnels is crucial to ensure the protection and healthy growth of crops. Thicker plastics, typically ranging from 4 to 6 mil in thickness, offer greater durability compared to thinner plastics. They can withstand multiple seasons of use and provide higher tear resistance, making them less prone to rips and tears. Thicker plastics also offer UV protection, preventing degradation from sunlight exposure and extending their useful life.
However, thicker plastics have some drawbacks. Due to their weight, they are more likely to sag or fall down when raised for ventilation. Additionally, thicker plastics can cause higher temperatures inside the tunnel during the day when closed, which may negatively impact the crops.
On the other hand, thinner plastics, ranging from 0.8 to 2 mil in thickness, are specifically designed for low tunnels. While they may be more prone to tearing and punctures, they offer flexibility and ease of use. Thinner plastics are also more cost-effective, making them a popular choice for farmers on a budget.
To enhance the durability of the plastic used in low tunnels, some manufacturers employ advanced extrusion technology, blending materials to achieve optimal strength, flexibility, and UV resistance. These plastics offer high tear resistance while remaining lightweight and easy to install. Additionally, certain coatings can be applied to the plastic to enhance its durability, such as anti-drip, anti-aging, and anti-fog treatments.
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Frequently asked questions
Polyolefin plastic film is a high-quality option that is tear-resistant and durable. It has a higher tensile strength and higher heat retention than cheaper plastics made from polyethylene.
Most greenhouse plastic is 6 mil thick, and this thickness should be sufficient for a low tunnel.
You can use plastic clips, called garden clips or snap clamps, to secure the plastic cover to the pipes.
