Sofia Martinez
Plastic greenhouses are increasingly being used in place of traditional glass greenhouses due to their lower cost and greater flexibility. However, the sun's intense UV radiation and heat can cause the plastic films to become brittle and dull within a few weeks. To address this issue, light stabilizers such as Tinuvin® XT 200 are added to the plastic to protect it from weathering and prolong its service life. Additionally, different types of plastic films, such as clear, white, or black plastic, can be used to control the amount of light entering the greenhouse, with some blocking up to 99% of light transmission. The choice of plastic film depends on the specific needs of the plants and the growing conditions.
| Characteristics | Values |
|---|---|
| Type of plastic | Polyethylene (PE) |
| Additives | Light stabilizers (e.g. Tinuvin, Tinuvin XT 200) |
| Light transmission rate | 87% is a good target figure for light transmission for plants |
| Thickness | 4-9 mil polyethylene non-woven |
| Colour | Clear, green, white, black |
| UV protection | Yes, UV-resistant plastics help extend the lifespan of the greenhouse |
| Heat protection | Yes, plastics can block or retain heat |
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What You'll Learn
Plastic films are more flexible and durable than glass
Plastic films are increasingly being used in greenhouses due to their flexibility, durability, and lower cost compared to conventional glass. They are made from polyethylene (PE) and typically last one year, but can be treated with light stabilisers to extend their lifespan. These light stabilisers, such as Tinuvin® XT 200, protect the plastic from the sun's intense UV radiation and heat, preventing the plastic from becoming brittle and dull.
Plastic films are more flexible than glass because they are pliant and shatterproof. They can withstand impacts from hailstorms, falling rocks, and other extreme weather conditions, making them safer and more durable than glass. Glass sheets, on the other hand, are brittle and delicate, prone to cracking under extreme heat or sudden weather changes.
The flexibility of plastic films also makes them much easier to handle and fit than glass sheets, which are bulky and heavy. This is especially advantageous for larger greenhouses or those in areas prone to harsh weather. Additionally, plastic films are more lightweight, allowing them to take on various shapes and sizes without sacrificing durability.
While plastic films are generally more durable than glass, it is important to note that not all plastics are created equal. For example, copolymer plastic is more resilient than standard polyethylene plastic, but it can become brittle over time, especially with exposure to harsh weather conditions. Polyvinyl plastic films, on the other hand, are known for their strength and resilience, lasting up to five years with proper care.
In terms of sun protection, plastic films can provide efficient light diffusion and UV protection. Some growers prefer plastic sheets as they offer better protection from radiation due to their UV treatment. UV-treated plastic films can manipulate the transmission of specific sun wavelengths, optimising plant growth. Additionally, coloured plastic films, such as green or red, can be used to filter out certain colours of light, providing an optimal spectrum for plant growth.
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Light stabilizers protect plastic from UV radiation
Greenhouse films are usually made from polyethylene (PE) and are produced worldwide. To make these films resistant to intense sunlight, light stabilizers are added to the material. These light stabilizers, such as Tinuvin, protect the plastic from the sun's intense UV radiation and the heat that develops at the contact points with the metallic greenhouse frame. Without these stabilizers, plastic films can become brittle and dull within a few weeks, with this effect being intensified by the use of some agrochemicals.
UV stabilizers are added to materials to protect them from ultraviolet radiation, which is found in sunlight and can cause the chemical structure of materials to break down over time by photooxidation. UV stabilizers work by absorbing, reflecting, or scattering UV radiation and preventing photo-oxidation. This helps to prevent issues such as fading, discoloration, and degradation.
UV stabilizers are used in a wide range of applications, including agro textiles, greenhouse film, mulch, and silage film. They are also used in products such as sunscreen, clothing, automotive paint, and building materials. By using UV stabilizers, farmers can increase the lifespan of their greenhouse films, enabling them to produce profitably throughout the entire growing season.
In addition to UV stabilizers, there are other ways to protect crops from heat and light during the summer. One method is to use temporary coatings, such as those offered by ReduSystems, which can be applied to the outside surface of the greenhouse. These coatings can extend the lifespan of a plastic greenhouse film by one to two seasons, depending on the climate and the properties of the film.
Overall, light stabilizers play a crucial role in protecting plastic from UV radiation, ensuring that greenhouses remain durable and effective for crop production.
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Thicker plastic may cause light diffusion
Plastic films are commonly used in greenhouses to protect crops from heat and light during the summer. These plastic films are usually made from polyethylene (PE) and are treated with light stabilizers to protect them from degradation caused by UV radiation and heat.
While thinner plastic films are typically used in greenhouses, thicker plastic films can also be used and may offer certain benefits. One important consideration when using thicker plastic films is the potential for light diffusion.
Thicker plastic films can cause light diffusion, which refers to the scattering of light as it passes through the film. This diffusion reduces the intensity of direct sunlight, creating a more uniform distribution of light within the greenhouse. This uniform light environment minimizes shadows, ensuring that all parts of the plants, including the lower leaves, receive sufficient light.
The reduced light intensity provided by thicker plastic can help prevent leaf burn and plant stress, promoting more balanced growth and higher yields. Additionally, the diffusion of light can enhance plant health by reducing the need for artificial lighting, resulting in more sustainable greenhouse operations.
However, it is important to note that the ideal percentage of light diffusion depends on the specific crop and greenhouse conditions. While a range of 70% to 80% diffusion is often considered optimal, thicker plastic films may exceed this range, leading to reduced light availability for the plants. Therefore, when using thicker plastic, it is crucial to monitor light levels and ensure that plants are receiving adequate illumination.
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Greenhouses with plastic sheeting are cost-effective
Plastic sheeting for greenhouses is a cost-effective solution for growers of all scales. It is a durable and effective way to protect plants from the elements while ensuring they receive enough sunlight to grow healthily.
The sheeting is made of reinforced polyethylene, with embedded polyester strings, which makes it resistant to tears and punctures. This means that the sheeting can withstand harsh weather, including strong winds and heavy snow.
The durability of the sheeting, combined with its UV resistance, allows it to last up to four years in typical outdoor conditions. This reduces the frequency of replacements, making it a more economical option compared to less durable coverings.
In addition to its longevity, plastic sheeting is also a flexible and strong option for greenhouses. It can be easily installed and adapted to various structures and sizes, including hoop houses, cold frames, and high tunnels.
Plastic sheeting also offers optimal light transmission, with 84% light transmission, which is ideal for most plants. The sheeting can also be purchased in different colours, such as clear, translucent white, or light-blocking black, depending on the specific needs of the plants.
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Plastic blocks some light and heat
Plastic greenhouse coverings are a popular alternative to glass greenhouses, offering greater flexibility and lower costs. However, the plastic used in these greenhouses needs protection from the sun's intense UV radiation and heat.
Plastic films used in greenhouses are often treated with light stabilizers, such as Tinuvin® XT 200, to prolong their lifespan by protecting them from degradation caused by UV radiation and heat. These stabilizers act as a barrier, blocking and diffusing a portion of the sun's radiation and heat.
The effectiveness of light stabilizers in plastic greenhouse films varies depending on the product and the climate. For example, in harsh conditions with intense solar radiation and high temperatures, the Tinuvin XT 200 stabilizer can provide a service life of up to 24 months. In contrast, untreated plastic films may only last one season before degrading due to sun exposure.
The colour of the plastic can also play a role in light and heat blockage. Green plastic coverings, for instance, are often treated to resist UV radiation, prolonging their lifespan. Additionally, the thickness of the plastic can impact light diffusion, with thicker plastics causing more diffusion. White polyethene, for example, is used when more shade is desired, as it allows only about 1% of light through.
Overall, plastic greenhouse coverings are designed to block and diffuse a certain amount of sunlight and heat while still allowing enough light transmission for plant growth. The specific amount blocked depends on the type of plastic, the presence of treatments or coatings, and the thickness of the material.
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Frequently asked questions
The type of plastic you should use for your greenhouse depends on your climate, growing season, and crop. Clear plastic coverings are the most common option and are great for plants that need lots of direct sunlight. They are capable of diffusing 23% of UV light with a total light transmission rate of 90%. However, they are unlikely to survive sunlight for more than one season. Thicker plastics may experience more light diffusion. White plastic is mainly used when shade is needed, while black plastic is used in light deprivation greenhouses that cultivate short-day plants. Green plastic is often treated to resist UV radiation, which means it can last two or more years.
You can extend the lifespan of your greenhouse plastic by using a temporary coating on the outside surface. Light stabilizers can also be added to the plastic to protect it from the sun's UV radiation.
Plastic films are much easier and more flexible to use than glass. They are also a more cost-effective option.
