Features to Look for in Greenhouse Plastics
When do I need IR, AC, or UV coating on my greenhouse poly?
Lighting and temperature inside the greenhouse depend on the type of greenhouse plastic used to cover the frame. Greenhouse plastic coverings are also called film or glazing. The plastic lets short waves of light through and blocks long waves that can be damaging. Radiation from the sun passes through the greenhouse plastic to transmit heat and light to plants.
Better quality polyethylene plastics can save you time and energy at marginally increased up-front cost. The following are some of the benefits of better plastics:
Improved Light Transmission: 87% is a good target figure for light transmission for your plants
Woven Plastic: Considerably a stronger due to cross-hatched fibers
Expansion & Contraction Resistance: Prevents plastic from getting blown out or distorted which can reduce light transmission
Anti-Condensate Coating: Helps prevent water from forming into droplets on the greenhouse film which helps with light transmission and prevents dripping on plants and the resulting spread of disease
UV Resistance: Helps with the life of your plastic, maintains clarity, and helps prevent yellowing and breakdown due to sun exposure
Greenhouse Plastic Features: Color
White poly is a greenhouse plastic that is mainly used when shade is needed. Panda film or black and white poly (white on one side, black on the other) is different than white poly. This type of greenhouse plastic is used in light deprivation greenhouses that cultivate short-day plants. You can see how this look in the picture below:
Choosing Greenhouse Plastics: Thickness
The thickness of the greenhouse plastic depends largely on climate and growing season. Here are some of the options you will see if you are looking to buy greenhouse plastic online:
4 mil poly and 5 mil poly is some of the thinnest greenhouse plastic that can be used to cover your greenhouse. These thin greenhouse plastics usually lack features like anti-condensate coating and anti-dust coating because the lifespan of the plastic is only about one year. Thinner greenhouse plastics are best used for greenhouses that do not operate year-round and are located in a mild climate.
6 mil polyethylene non-woven is a very common choice for greenhouse covering. This type of greenhouse plastic has a four-year lifespan. It is inexpensive because it is non-woven, and 6 mil is still fairly thin. Infrared and anti-condensate additives are features that help extend the lifespan of the plastic and reduce moisture accumulation. If you live in a climate with mild to moderate conditions, 6 mil non-woven poly could be a good option.
9 mil polyethylene non-woven is thicker and more durable than 6mil and is a better option for greenhouses in climates that experience severe weather and snow. The same features are available as with the 6 mil poly:
- Anti-condensate Coating
- Anti-dust Coating
- UV Protection
- 4-year lifespan
12 mil poly is very thick and can create light diffusion that diverts energy away from crops. However, in certain applications, this ultra-thick woven greenhouse plastic could help offer insulation and strength needed to withstand harsh climates and severe weather.
Light Diffusion With Greenhouse Plastics
Light diffusion in a greenhouse can divert usable energy away from crops. In general, light diffusion is something that people want to avoid. Here are some tips for avoiding light diffusion:
- Use clear greenhouse plastic
- Replace discolored greenhouse plastic
- Use a greenhouse plastic with anti-dust coating
- Use ventilation to help reduce dust and particle accumulation
- Keep the greenhouse clean
Insulation From Greenhouse Plastics
If you are a year-round greenhouse grower, or a grower located in a climate that experiences freezing temperatures, you have even more reason to buy high-quality greenhouse plastic. Not only will the glazing need to withstand the weight of the snow, but it will also need to keep heat in and conserve energy. The R-value will tell you if a material has good insulation properties. The higher the R-value, the better the plastic will be at insulating.
General Overview of Greenhouse Covering Insulation Properties
|Glazing Material||R-Value||Light Diffusion||Description|
|Polyethylene Film (single pane)||0.85||Semi-diffused||Inexpensive, easy to replace, good for large greenhouses, must replace every few years, most common|
|Polyethylene Sheeting||2.1 to 2.3||Diffused||Lightweight, stiffer than film and better insulation, UV resistant|
| 1.43 to 1.89
||Diffused||Light but durable, light transmission degrades from UV discoloration, lasts 15+ years, difficult to use with curved designs|