Anyone who is just getting into horticulture should know about the amazing things you can do with a greenhouse. These artificial structures have made it possible to grow plants, flowers, fruits, and vegetables throughout the year. They also allow you to grow exotic plants and flowers that wouldn’t normally survive in your climate (https://www.gardeningknowhow.com/special/greenhouses/greenhouse-tree-care-growing.htm).
Greenhouses are able to perform these feats by creating and maintaining an artificial climate. Some plants tend to be very sensitive to environmental changes, so you should ensure that your greenhouse is able to maintain the conditions you have set.
Many greenhouses use plastic to trap heat and moisture within their structure. If you want to learn what kind of plastic to use for your greenhouse, you’ve come to the right place. Let’s look at the different types of plastic used for these remarkable structures.
Why use plastic for your greenhouse?
Whenever the term “greenhouse” is used, people tend to picture an outdoor structure composed of glass panes. However, many of the structures people mistake for greenhouses are actually conservatories, which aren’t suited for growing and nurturing plants.
Glass greenhouses do exist, but most modern greenhouses are constructed using plastic. This material offers many advantages over glass, which makes it a popular choice among growers. Some of the benefits of using plastic over glass in a greenhouse include:
Better insulation
Plastic offers better insulation compared to glass due to its lower thermal conductivity. Heat trapped within the greenhouse will have a harder time escaping via conduction through plastic material. This allows plastic greenhouses to maintain higher temperatures more effectively than glass ones.
Longer lifespan
Some types of plastic, such as polycarbonate may survive longer than glass. This material can undergo large plastic deformations without breaking. Due to these properties, a sheet of polycarbonate can withstand far more damage than glass.
Easy replacement
Greenhouse plastic is also easier to replace and install yourself. Plastic is lighter and more flexible than glass, which makes it easier to remove and fit into your greenhouse. Replacing a broken glass panel is a more challenging task and usually requires the assistance of a professional.
Better light diffusion
Plants grow better in greenhouses when they receive an even spread of diffused light. Since plastic sheets are usually thicker than glass panels, they can diffuse light more easily. Plants in glass greenhouses have a higher chance of burning from exposure to direct light transmission. (https://www.acplasticsinc.com/informationcenter/r/polycarbonate-sheet-is-a-better-investment-than-glass)
Some types of plastic, such as acrylic and polycarbonate, are also naturally good at filtering out UV rays that could damage plants. Using these plastics instead of glass panels helps protect your plants from some of the Sun’s radiation.
Affordability
Greenhouse plastic is also more affordable than greenhouse glass. This makes it a great choice for people with low budgets. Plastic’s durability also means it won’t have to be replaced as often, which adds to its cost effectiveness compared to glass.
Factors to consider before choosing plastic for your greenhouse
Your greenhouse plastic needs may vary depending on the climate you live in. If you live in a northern state, you will need to focus on choosing a material that conserves energy. Conversely, if you live a warmers southern state, you will need to choose a material that offers better shading.
Let’s look at some of the factors that could influence your choice of greenhouse plastic.
Energy conservation
Energy costs can be a major factor when it comes to choosing a material for your greenhouse. If you live in a cold climate, you will need a material that offers good insulation in the winter. Greenhouses located in hotter areas can get by with weaker insulation.
A material’s insulation properties can be assessed using its R-value. Greenhouse plastics with higher R-values tend to be better insulators than plastics with lower R-values.
Durability
Your greenhouse’s external covering will be exposed to the elements throughout the year. For this reason, it’s important to select a material that is capable of handling whatever mother nature throws at it. Depending on where you live, your greenhouse may have to weather through strong winds, heavy rains, and snowstorms.
Your greenhouse material should also be able to stand up to sunlight exposure. Some plastics, such as polyethylene, are known to become brittle from exposure to UV rays. This can shorten their lifespan. However, many polyethylene coverings feature UV-stabilizers that reduce the rate at which the material degrades under sunlight.
Thickness
The thickness of your greenhouse plastic can also affect its re-usability. 3 or 4 mil film lasts up a year when it is used on narrow tunnels and overwintering greenhouses. Thick film, such as 6 mil, offers better durability and can last multiple years with the right care and maintenance.
Condensation control
Some forms of plastic for greenhouses feature anti-condensate. This is a wetting agent that alters the material’s surface tension. Anti-condensate prevents water from beading together and forming droplets.
You generally want to avoid having water droplets present on your greenhouse plastic because they can partially block light from reaching your plant. Excess condensation dripping onto the plant can lead to disease problems.
Infrared (IR) film
Some plastic for a greenhouse feature an infrared film that helps keep out or trap infrared radiation. Some double layer poly installations feature this film on their underside. This feature helps retain night time heat and keeps your greenhouse warm.
It is believed that increased night-time temperatures help retain plant color and boost crop development rate (https://www.greenhousemag.com/article/gmpro-0510-choose-right-plastic-film-polyethylene). Greenhouse film with an infrared film cost a bit more than average, but they can be useful for growers living in cold climates.
Conversely, infrared films located on the external surface of greenhouse plastics can reduce heat gain during the daytime. This can be useful in areas that receive lots of sunlight, as infrared radiation tends to raise the temperature inside the greenhouse. Setting a cooler artificial climate within your growing area helps with plant development, lowering energy bills, and creating a more comfortable environment to work in.
Number of layers
If you are using a clear plastic film to cover the plants in your greenhouse, the number of layers could make a significant difference to their growth. Many growers operate using a single film for this purpose. However, a double film will be required when the greenhouse is being used during warm summer months.
This double layer helps trap heat and reduces heat loss at night. A double layer is also more durable than a single layer, as it is less likely to rip or tear at the edges where it has been fastened.
What types of greenhouse plastic are there?
Greenhouse plastics can be divided into the following two types:
- Type I: These are “glazing” materials, which resemble thin plastic films. Some common greenhouse film includes polyethylene, polyvinyl chloride (PVC), and polyester films.
- Type II: These are hard plastic panels. Some common examples include polycarbonate, acrylic, and fiberglass-reinforced plastic (FRP),
Type I plastics
Plastic films are popular choices for greenhouse plastic because they are lightweight and easy to install. They do not require structural support systems, so they can be put up in just about any greenhouse.
Polyethylene film is the most common type I plastic used in greenhouses. This material is affordable to purchase, comes in large sheet sizes, and offers good light transmission. This material also includes anti-dust additives that reduce the likelihood of dust accumulating on them. This is a beneficial feature because dust can reduce light transmission, which could affect plant growth.
Farm Plastic supplies a great 6 mil greenhouse film that comes with a four-year warranty. (https://farmplasticsupply.com/4year-clear). Farm Plastic also offers many greenhouse films that are white or clear, depending on your preference (https://farmplasticsupply.com/greenhouse-films).
Polyvinyl chloride (PVC) film offers good resistance against regular wear and tear. This material prevents infrared radiation from entering or escaping your greenhouse, which can be useful for reducing heat loss during the night. However, heat and light can break this material down in 2 to 3 years, so it may have to be replaced every couple of years.
Polyester film tends to be more expensive than the aforementioned film options; however, it offers better durability and a longer life expectancy. This material does not generate static, and is less likely to attract dust compared to other films.
Type II plastics
Hard plastic panels offer good light transmission, but this quality may decrease over time with sun exposure. After a few years, you may notice your panels changing color. These materials are heavier than films, but much lighter than glass. They are useful for most greenhouse shapes, but they can be tricky to install on curved or domed roofs. http://www.greenhouse-management.com/greenhouse_management/greenhouse_glazing/types_greenhouse_glazing.htm
Polycarbonate
Polycarbonate is one of the most popular greenhouse plastic choices. It transmits light better than polyethylene film and offers great heat retention. This material’s transmission of light is slightly lower compared to acrylic, but it offers better strength and fire resistance. With the right care, polycarbonate panels can last 10 to 15 years
Acrylic
Acrylic is a rigid form of plastic that is usually transparent. This clarity allows you to view the inside of your greenhouse, and transmits light incredibly well. Acrylic is also known to be flame retardant and fares well against impacts. If you live in an area that receives hail, you may want to consider this plastic for your greenhouse.
Fiberglass-Reinforced Plastic Rigid Panel
This material was more popular in the past, but it is still used in some greenhouses. Fiberglass panels come in flat or corrugated styles. The corrugated variety is sturdier than the flat variety. This material is flexible enough to use for curved roofs.
Frequently Asked Questions
Here are some frequently asked questions about plastics for greenhouses.
Q: How thick does the plastic need to be for a greenhouse
A: A 6 mm film is recommended for greenhouses as it will last for multiple years. However, you can use a 3 or 4 mm film if you don’t intend to use them.
Q: What is the best material to use to cover a greenhouse?
A: Polyethylene film is the best material to use for a greenhouse that doesn’t feature a lot of support structures. If you wish to use panels, polycarbonate is the way to go.
Q: Can I use 6 mil plastic for a greenhouse?
A: 6 mil plastic can be used for a greenhouse. This material can be reused multiple times with the right maintenance.
Conclusion
There are many types of greenhouse plastic available for growers. These can be categorized as either plastic films or plastic panels. Films are easier to install, but they may not last as long as panels. Polyethylene film is the most popular greenhouse covering because it is cheap, comes in large sheets, and offers great transmission of light. Polycarbonate panels are the most popular panel coverings for greenhouses because they are durable, offer good heat retention, and last for a long time.
Leave a comment if you have any questions.