Controlling and making use of the heat and light energy is relatively easy. The beauty of growing in a greenhouse is that you can extend growing season and increase production. Who doesn’t like to look after plants year round without worrying about rain and wind?
Most of the time gardeners aim to increase humidity, control air flow or heat up the greenhouse structure without electricity. Sadly, greenhouse lighting requirements are often overlooked. Understand what light plants really need will make the difference in production.
Many growers believe that it is crucial to maximize all available light to provide optimal growing conditions. However, what plants actually need is a diffused and not a direct light. You might be confused at this point, so let’s start from the beginning. There are two types of natural light: direct and diffuse.
Direct light consists of sun’s direct rays. Diffused light consists of scattered light waves. Direct light turns into diffused light when it passes through translucent material. Examples of translucent materials are frosted glass and some plastics.
In nature diffused light occurs when sun rays are scattered by the atmosphere or clouds. In comparison to translucent material, transparent material like regular glass let light to pas through the material without scattering it.
When choosing greenhouse glazing you need to keep in mind these properties. That is why when choosing plastic for a greenhouse a question pops up – does greenhouse plastic have to be clear?
If you are planning to use a greenhouse for germinating seeds and starting plants which will then move outside, plastic has to be clear because it will let direct sunlight that heats up the soil and encourages germination. However, if you want plants to mature in a greenhouse, get opaque or frosted plastic which will provide diffused light.
There are different types of greenhouse glazing material but the most common are polycarbonate and glass. In this blog post we will talk about their diffusion properties and if green plastic is better for greenhouse.
Clear vs opaque (frosted) greenhouse plastic
The most common greenhouse covers are plastic and glass. Regular glass is a transparent material, so it allows light to pass through without scattering it. Direct light, which gets to a greenhouse, is intense, forming shadows and burning rays.
Alternatively, twin-wall polycarbonate cover is a translucent material which partially diffuses light but still tends to overheat. Diffuse light wraps around plants and reaches lower leaves as well as top leaves. That way plant energy production increases during photosynthesis.
The pros of using clear greenhouse plastic is that it delivers direct light into the structure which heats the soil providing optimal temperature for seed germination. Only use clear plastic if you use greenhouse for germinating seeds and growing starters for transplanting outdoors.
Direct light encourages germinating seeds to sprout and develop into strong seedlings ready for transplanting outdoors. For this purpose you need to choose clear covers like glass, single-wall polycarbonate and acrylic plastic. You can check what is the best glass for greenhouse in this post.
What plastic is best for greenhouse?
The main disadvantage of using clear vs opaque or frosted greenhouse plastic is that direct light creates hot spots while leaves other plants in shade. It also produces excess heat that is trapped in the greenhouse. In a meantime opaque plastic scatters light waves and provides even light for optimal plant growth.
Diffuse light reaches all areas of greenhouse and produces the the most efficient photosynthesis. Also, because it reaches plants at different angles they are not leggy as they don’t try to grow towards available light. It is especially important if you are growing tall vegetables or growing vertically on benches.
Finally, diffused light reduces fungus spore development and insect propagation. Opaque or frosted greenhouse coverings like polyethylene film, fiberglass and Solexx provide the best light diffusion. Some greenhouses also come with semi-diffused covers.
It is a perfect option for someone who wants to use a greenhouse for propagation in early spring and for growing plants all year round. A semi-diffused greenhouse most of the time has diffused covers on the roof and clear plastic on the sides. That way you can have an all-purpose greenhouse!
Green or clear plastic for greenhouse?
Green greenhouse plastic cover reflects a large portion of green waves and allows to pass through the rest of the light spectrum. As you know the colors of the spectrum are red, orange, yellow, green, blue, indigo and violet.
Plants need blue waves during growing and maturing stages and red waves during blooming and producing stages. They hardly absorb any green light, so the green color reflect back into our eyes and that is why leaves appear green.
Also, during photosynthesis a pigment chlorophyll just absorbs blue and red light and the green light is reflected out since the pigment does not absorb it. Essentially, green plastic cover will filter out green light and pas through the rest of the spectrum when clear plastic lets in the full spectrum of light inside greenhouse structure.
Are green polytunnels any good?
Using green color plastic for greenhouse is beneficial if you live in hot climate regions because it lets in 78 to 90 percent of natural light, so sun energy will not be converted to heat and will help to cool down the greenhouse.
However, if you are choosing between green or clear plastic for greenhouse, go for clear option and use a green shade cloth to cool the greenhouse. To achieve green plastic color manufacturers can use chemicals which might leach.
To sum up, if you are growing plants long term in a greenhouse, go for opaque or frosted plastic and not clear plastic as well as stay away from green color plastic. If you want to filter out different wavelengths, use different colors shade cloths instead.
What plastic (clear of opaque) do you use for your greenhouse? Let me know in the comments section down below!
Happy growing 🙂