Greenhouses are a great way to expand your gardening capabilities. Whether you use them just to get plants started or keep plants growing in there full-time, greenhouses offer a stable growing environment, trap in precious moisture, and protect plants from weather. If you’re considering a greenhouse, you may be wondering whether a plastic one is a good option.
What are the pros and cons of a plastic greenhouse? Here are the top 6 considerations:
- Heat retention
Most of these factors are in comparison to glass greenhouses. There are more details and factors to consider when you decide on your greenhouse building material. We’ve gathered a few questions and answers you should check into before moving forward.
6 Pros and Cons of Plastic Greenhouses.
The transparent material that makes up the walls and roof of your greenhouse is called “glazing.” There are several types of plastic glazing you may choose for your greenhouse. We’ll get into all of those options later. Right, now let’s focus on the pros and cons of choosing plastic in comparison to glass.
Pro: Cost is usually lower
Cons: Can vary in cost depending on the plastic and its durability
One huge benefit of plastic glazing is the price. Plastic greenhouses will generally start at a lower cost. Smaller and plastic greenhouses can be found for under $100 online like this one available on Amazon.
The main difference in price will be the shape of the greenhouse, construction, building material, style, and overall size that you are looking for.
Keep note that these prices can mainly differ in the type of construction material and plastic that you want to use for your greenhouse.
If it is not a pre-built glasshouse you are looking for (like the example given previously), you will have a lot of more options to pick from when regarding your greenhouse build material.
Since plastic materials for greenhouses are popular, there are also various types of plastic and sheaths of plastic that are available. More on this later in the upcoming section.
Pro: It’s easy to install plastic, which means cheap labor! It is also much lighter and requires less structural support.
Installation might as well be a subcategory to the cost. Since it is much easier to install and replace plastic panels compared to glass, it is cost-saving but also beneficial to labor cost and labor time.
After all, time is money, and in addition, time waiting on a repair or installation affects how quickly you can get your plants’ environment in good order.
If you also want to save more money, you can also go with lighter glaze options to keep the cost down on the structure of the greenhouse. The less weight it has to bear, the supporting structure material and build style can be easily adjusted to fit your budget.
There are also helpful videos on how to install plastic covers like this polyethylene cover video:
3. Heat Retention
Pro: Pretty high heat retention
Con: Will depend on the region/climate you live in and the type of lights you get. It could be too much heat retention in some places.
Depending on how much heat you want (for instance, this could be less for those that live in Texas), consider what kind of material you want to build the overall greenhouse with.
This can be a stark difference between glass and plastic.
For plastic, you will have higher heat retention and good insulation. Most plastics will have properties that outperform heat retention in comparison to glass.
There are methods of providing different levels of heat retention, such as layering several sheaths (popular double-layered configurations), which are simply separated in between with a layer to help with the glaze.
Multiple sheaths help retain heat and provide high insulating values but also strength. If you live in colder regions and want to retain the heat from the sunny afternoons into the cooler nights of the evening, multiple sheathing is the way to go.
Pro: Thicker options are even more weather resistant than glass, easier to clean, and easier and cheaper to replace
Cons: It could easily fade and yellow making the plastic less preferred for transmittance and aesthetic purposes
There are many explanations for the longevity of the plastic greenhouse:
- Plastic greenhouses in comparison to glass greenhouses are generally stronger (as mentioned previously).
- If the plastics are provided in multiple sheaths, then they are stronger and more durable, but on the flip side, plastic can also be seen as less durable if you are choosing a thinner glaze option. Thin options can tear or rip and would need replacement due to wear and color change. If the glass is broken or cracked, it would be hard to clean and expensive reinstall, but a small break would be easier to patch up.
- Plastic stands up to weather well and is durable to physical impacts such as hail or other objects that may impact it. There are more options that are shatter-resistant (in comparison to glass options).
Side note about safety: If you also have kids (or the ones with four feet and paws) that may run around the glasshouse, you may want to consider plastic for the safety aspect of it. If it breaks, it won’t leave the glass on the floor, and the replacement of it will be a lot easier and cheaper.
One thing to look into in the upcoming section is the type of plastic to buy. Depending on the plastic, there could be some that are more durable simply because it doesn’t expand and contract too dramatically during the seasonal changes.
5. Transmittance of Light
Pro: There could be more control on transmittance, depending on the glaze and number of sheaths.
Cons: You may or may not want more or less transmittance and diffusion.
The transmittance – or simply the amount of light and type of light you want in your greenhouse – is an important factor you need to consider for your plants.
Most plants will require light that is from the visible light spectrum, which is called photosynthetically active radiation (PAR) transmittance. Both glass and plastic options provide this transmittance (just make sure before you purchase!)
How Much Transmittance of Light Do Your Plants Need?
Depending on the type of glaze, there can be different amounts of transmittance. A single layer glaze can transmit up to 90 percent, and with a double layer glaze, you can see a decrease of transmittance at 80 percent.
Direct or Diffused lights?
The diffusion of light that your plants are exposed to can be controlled by the type of glaze as well. Light is identified as direct or diffused, depending on:
- The type or amount of glaze
- The concentration of contaminants in the air
- Different reflection factors of the lights that are entering the greenhouse
Although there are benefits of direct lights, a diffused light disperses lights to more crevices of the glasshouse that would normally not get a lot of exposure to the light rays. This increases the chances of different plants and different parts of the plants to receive the lights.
Theoretically, a double glaze (plastic) will be optimal as it will help with the deflection of the lights to further diffuse throughout the greenhouse.
With this in mind, now there are types of glazes that target this behavior. There are certain plastic glazes that are able to change this type of diffusion and selectively filter the acquired wavelengths from the sun.
The shape of the greenhouse can take a huge part in the angle and amount of transmittance you want.
6. Aesthetic of the Material
Pro: Various options
Con: Most people like the look of the traditional glass
In general, without considering specific shapes and build, there is a general preference to the glass greenhouse aesthetics than the plastic. Glass provides a clear and reflective look that is more traditionally seen as the classic greenhouse.
Plastic tends to have more of a translucent look that can also yellow in a short time frame, then at worse case wear and tear. It isn’t always as visually pleasing as glass.
Are Plastic Greenhouses Any Good?
Whether a plastic greenhouse is good will depend on the region and climate of where this greenhouse will be built and the type of plants that will be grown in the greenhouse.
Read on to see what shape of greenhouse you will need to consider depending on the region you live in and also what best suites your ideal greenhouse set up.
That being said, there are different types of plastic greenhouses, and they are comparable to glass greenhouses.
What Kinds of Plastic Greenhouses Are There?
There are different types of plastic glazing to choose from, but the two main genres split into plastic films or the thicker polycarbonate panels.
Let’s just break it down to look at the three main types. There are advantages and disadvantages to each material selection and the best
Polycarbonate vs. Glass vs. Plastic Films (Polyethylene)
Here is a comparable list of the common areas of advantages we’ve discussed previously:
|Categories||Polycarbonate (Plastic)||Plastic Film||Glass|
|Installation||Easy Installation||Easy installation and fix|
|Heat retention||High thermal efficiency|
|Longevity||Good longevity||Best longevity|
|Transmittance||Slightly diffused light||High diffused light||Light clarity|
|General Durability||Tough and Durable||Takes knocks well|
|Categories||Polycarbonate (Plastic)||Plastic Film||Glass|
|Heat retention||Poor thermal efficiency||Poor thermal efficiency|
|Transmittance||High and strong clarity|
|Aesthetics||Scratchy||Clarity is short-lived|
|General Durability||Moisture and mold entrapment. Sealing is required||Prone to rips and tears||Fragile and not good with knocks|
- Overall a polycarbonate is most preferred if you are looking for a thermally efficient and easy to use greenhouse material.
- Most polycarbonate setups are with the double to multilayer configuration with a flute in the middle. This is what provides the glazing effect mentioned previously.
- If you use polycarbonate that is made from new raw-material and not recycled material, it will help with enhancing the glazing effect.
- Many recommend that polycarbonate sheaths are also UV protected. This can be something you can make sure with the supplier before you purchase.
- Varieties in polycarbonate greenhouses vary in their thickness. Thickness can range from 10mm to 20mm and how many layers of it will be used (commonly twin-wall to tri-wall).
Polyethylene Plastic Films
Plastic films, also known as poly-films or AgPhanes, are a great alternative to polycarbonate when it comes to being budget-friendly. They have a significantly low cost per square feet and are generally easy to install.
- Depending on the climate of your region, windy or heavy snowfall, you will need to consider its durability and what kind of supports will best hold up the plastic films. We have an article here that goes into more depth on some important things to consider to help you determine if yours might blow away including some ideas how to secure greenhouses in order to prevent that from happening.
- For most growers, plastic films are layered in double-layer systems. This helps with the rips and tears from debris.
- To compensate for the low thermal efficiency, some commercial growers use warm air in between the layers (e.g., between a double layer), to help with the insulation and keeping the temperature of the greenhouse at a certain value.
- Although polyethylene films are cheaper on the budget, they are subject to more frequent replacements. As the films tend to lose their clarity with time and often change in color (opaque, yellowing, etc.), it is commonly changed out every 3 to 5 years.
The clarity and type of wavelength that enters the greenhouse are crucial for your plants so frequent replacements will be something you need to consider if you go with this choice.
Like the polycarbonate option, polyethylene films can vary in thicknesses and ways of layering. Here is a shortlist of recommended polyethylene films:
|UV-Protected||Limited sizes (2 sizes)|
|Affordable, good price||Larger size option not available|
|91% light transmittance|
|Cheapest option in the list||Larger size option not available|
|UV-protected||Opaque than most films|
|Diffuses light (well)|
|Comes in multiple (8) sizes|
|Affordable, good price||Larger size option not available|
|92% light transmittance|
|Comes in multiple (14) sizes|
|UV-protected||More expensive than most options|
|Fairly durable||Does not come in small sizes|
|Comes in multiple (8) sizes|
|Longer warranty option|
|UV-protected||Most expensive in the list|
|5 layer technology – durable||Does not come in small sizes|
|90% light transmittance|
|Comes in multiple (11) sizes|
Do Shape and Location of a Greenhouse Matter?
The last part of this review will be about selecting the greenhouse shape and location. As the main concern may be selecting the right material to build your greenhouse, you should also consider the shape of your greenhouse.
The climate or general weather conditions in your region will be what determines what kind of thermal efficiency you will need, what angle roof you might need, and what kind of material will work best for you and your plants.
Greenhouses can either be an attached lean-to style, attached even-span, attached window-mounted, or free-standing.
Let’s focus on free-ranging greenhouses here. There are six major types of freestanding greenhouses:
- Gothic arch
- Raised Dome
Most of these shapes can determine what kind of plants you want to grow. For example, tall trees or multiple shelves may best work with the gable roof style as you have more of a vertical space.
Choosing the Pitch for Your Greenhouse Roof
In general, most greenhouse designers recommend taking your latitude and adding 20 degrees. This is a simplification, and more things should be considered for your greenhouse to be sufficiently nurtured throughout the year.
Depending on the glazing and the angle of the glazing, your light transmittance and overall degree of the roof will change.
To best apply this concept, follow the two steps below:
- Take your latitude and add 20 degrees to get the perpendicular (90-degree) angle of the sun during your winter season.
- Take this number and subtract 45 degrees. This will be the minimum angle before significant light transmission is lost due to reflection.
Relationship Between Climate and Roof Slope
If you are in a heavy-snow fall region, you may want to consider steeper roofs as it will shed snow much easier. This will be less pressure on your structure and panels, which will help its longevity and durability.
Less Steep roofs
If you have a very steep roof, it could be less convenient in the summer-time. This could lead to more reflectance rather than transmittance when the sun is generally high at a sharp angle.
The secret is that selecting the right shape is your tool and money. If you select the right slope, match it with a good transmittance amount and angle, you will have a greenhouse that is productive throughout the year regardless of the season.
If you want to learn more about it, start with this book available from Amazon on building a year-round solar greenhouse!
Selecting Greenhouse Location
Location is very important when setting up your greenhouse. You want to provide optimal sunlight and also provide good amounts throughout the year.
Setting up your greenhouse where the lengthwise North-South is optimal for most regions as it has less shade and more light can be received in comparison to setting up a greenhouse that has its lengthwise in the East-West.
This is generally a good set up for limited light intensity. Whether you are in a region with limited sunlight hours or it is during the winter months.