What Material Should I Use for My Greenhouse Covering

Which Material is Better for greenhouses, Glass or Plastic?

Good Question and we’re going to answer it. But first, we have a question for you.

What do you get when you combine a physician, a cucumber, and an Emperor of Rome? A strange query, no doubt. But before you get too humorously creative, we’re going to give you the answer. And that answer is, a greenhouse. That’s what you were thinking, right?

What material is used for greenhouses is essentially based upon your needs, preference and budget. A greenhouse can be very large and expensive to build or quite small and made on the cheap depending on size and materials. Galvanized steel costs more than aluminum. Glass, tends to be more expensive than plastic. Especially should you use double-paned glass.

To see how all this greenhouse business got started…let’s go back to the very beginning.

A Bit o' History

Legend contends that around 30 A.D., the physicians of Roman Emperor Tiberius recommend he eat one cucumber a day to maintain his health. It was no secret Tiberius was a great lover of cucurbits (KYOOcur-bits), which are gourds in the family of melons, squash, zucchini, and as the name suggests, cucumbers.

Keeping Tiberius supplied was not an issue during the growing and harvesting season. The problem arose when the storage bin ran out of cucs and Tiberius had to wait until the next growing season to enjoy one. No surprise, there was nowhere to get fresh cucurbita (plural form) in the dead of winter or if a crop flooded out or was stricken by drought.

Rome...We Have a Problem

Realizing that ticking off Tiberius wasn’t in their best interest, the Emperor’s engineers set to work on solving that problem, eventually coming up with the solution. They designed and implemented what is widely considered to be the first specularia…the Roman Greenhouse.

Naturally, it bore no resemblance to the greenhouses of today. Indeed, greenhouses have come a long way since the days of Tiberius, as have the materials used to construct them. Especially, when it comes to the material used to cover the greenhouse.

Crude but Effective

The first greenhouses were constructed atop open, wheeled carts. These carts were large enough to grow vegetables in, yet, small enough to be manageable and moveable. Creating a garden that was readily mobile held an immediate advantage over traditional, stationery gardens.

Without the benefit of today’s greenhouse plastics and modern glass to protect their garden plot, these carts were often framed using mica, a translucent silicate mineral thin enough for light diffusion and offered some protection from the winds and rain and even a too bright sun. 

This new method of growing ensured Tiberius stayed happy and well-stocked with his beloved cucurbits. What seems crude by today’s standards with the advancements made in greenhouse covering, like clearer glass or tinted or even polycarbonate sheets, in its time, the Roman Greenhouse was a revolutionary concept.

Fast Forward To The Past

It took nearly 1700-hundred years before the greenhouse reached the shores of America. Wealthy store merchant, Andrew Faneuil, is credited with building the first greenhouse in Boston, Massachusetts, way back in 1737. Since then, greenhouses and greenhouse construction have come along way in their development, design and efficiency.

As the idea of growing food under a roof and year-round spread quickly, the greenhouse revolution was born. Protected from the elements, vegetables, shrubs, flowers and even trees, could now be grown year-round with a good degree of success. This was of tremendous benefit for those living in parts of the world with shortened growing seasons or those people who simply enjoy puttering in the garden during those unfriendly rainy or cold, wintry months.

From Tiberius to Today Greenhouses Then and Now

Greenhouses and the greenhouse structure have made some tremendous strides since the cucurbit days and its burgeoning beginnings in early America. Let’s jump ahead to the modern day greenhouse. While appearing much different than their early predecessors, today’s greenhouses serve the same purpose as those original greenhouses of ancient Rome.

The modern greenhouse offers the gardener a number of materials from which to choose. From protective glass to newer plastics like polycarbonate panels. There is practically a greenhouse for everyone and within most folk’s budget. New developments in the efficacy of plastics that come in a host of price ranges, also offer much improved light diffusion than the old brittle plastic coverings.

Next to design, the obvious differences are the advancement made in the materials used to cover greenhouses.

Let’s look at some and we’ll start with one of the most common in the early to mid-twentieth century and still to this day.

Glass Greenhouses

In the last century, and before the technical development of specialized greenhouse plastics, the great majority of greenhouses were covered in glass panels. Glass provided the perfect medium for indoor plant growing by keeping plants warm, weather-proofed, and bathed in constant sunlight. Plus, they generated heat via the sunshine.

The greenhouses were also made sturdier with the advent of galvanized steel used for framing. Galvanized steel is steel that has been coated with a layer of zinc to prevent corrosion. Galvanized steel was a major improvement. Aluminum is also used, but generally as poles for smaller greenhouses.

It’s easy to see why galvanized steel became so popular. In addition to its anti-rusting properties, galvanized steel is strong and a top choice of industrialists due to its sturdiness and is especially used in constructing greenhouses that operate commercially.

A greenhouse structure framed with galvanized steel is designed to last and will provide years of solid protection for your plants regardless the material you cover it with, be it glass or a plastic material.

A Downside to Glass?

As good as glass is at insulating and allowing light to enter the grow room, it is not without its drawbacks. Glass is susceptible to being cracked or broken by falling limbs or branches, especially under windy conditions. You also don’t want to be working under a broken glass panel from the ceiling, either.

In addition to having to remove the broken glass panel which can be a bit tricky, the glass panels also require resealing each time one is replaced to ensure there are no leaks which can be time consuming and a pane to deal with. Glass greenhouses can sometimes cost more to construct and can get pretty dirty after a summer of rain or if there are large trees close by that drop twigs and leaves.

Glass Alternatives

Some gardeners prefer not to use glass on their greenhouse and instead, opt for plastic in an effort to protect birds from flying into it. Unfortunately, this is not so rare an occurrence with glass greenhouses. Birds tend to see the clear glass as open sky. Much like house windows that reflect a blue sky replete with clouds and trees.

While glass undoubtedly has a scorecard of benefits, it is gradually being usurped in many greenhouses by improved sheets of strong polymer plastics. Polycarbonate panels and polycarbonate sheets keep heat in and cold out. Especially those with double wall construction.

Size Doesn't Matter

Keep in mind that greenhouses don’t have to be large buildings with a football field of ground space. A good many backyard gardeners do quite nicely having a size-to-need greenhouse structure in which they grow their plants. A home-made, plastic greenhouse can prove very effective for growing a variety of flowers, vegetables and even some fruits.

It stands to reason a smaller plastic greenhouse is going to cost less to construct than a large glass greenhouse. There are also kits available to build your own greenhouse. For some people, that is the way to go. These kits range from complicated to easy to construct. They provide adequate heat in winter but sometimes a small heater is needed to give a little extra heat to the plants.

Plastic Replaces Mica and Glass

With the advent of plastic film, greenhouses have attained new levels of efficacy. Many indoor growing facilities being built now, use as their covering material various types of plastics as their sheath.

Greenhouse plastic or greenhouse film as it is also known, offers the buyer more options than standard glass panels do. Lightweight, cheaper, and less likely to break or crack, these newer plastics come in sheets rather than separate panels and are becoming the greenhouse covering of choice for many home gardeners.

Let’s take a look at four of the most popular and commonly used greenhouse films. Or greenhouse plastics as they are known. Below is the answer to the title of this article.

Polyethylene

Polyethylene plastic is popular with gardeners and used as greenhouse covering because it is lightweight and adequately functional. Polyethylene can be ordered in two thicknesses which are measured in millimeters. There is a utility-grade greenhouse covering for the backyard gardener and a thicker, more durable version offered as a commercial-grade for industrial applications.

Polyethylene as your greenhouse covering is a popular choice but only lasts a year or two according to the experts. And while that could seem problematic for the long term grower, this covering material holds some advantages. Small rips or tears can be easily patched up using a poly repair-kit. Additionally, being that it is a cheaper grade of greenhouse covering, it is less expensive to purchase than the others listed here but is still quite effective.

Copolymer Greenhouse Plastic

Copolymer plastic is a step above polyethylene and is more durable and longer lasting than the aforementioned greenhouse coverings, as they are now called. Two to three years of good use is not uncommon. Weather is the main threat. The constant freezing and thawing, heating and cooling, will eventually cause the plastic to become brittle and cracking can eventually occur. Higher grade copolymers are available that will last longer but they will also cost you more money.

Polyvinyl

Polyvinyl is an even better grade of plastic material, more durable and longer lasting than the previous two plastics. And as you might suspect, costs more to buy. Polyvinyl Chloride is an extremely versatile material and comes in two forms, rigid and flexible. You may know the rigid version as this is used to make PVC pipe. Being rigid, it may be listed RPVC.

The flexible form is used to make everything from greenhouse covering to food wrapping, and from credit cards to vinyl records. As a stronger grade of plastic, polyvinyl can last five-years or longer with regular maintenance and care. Polyvinyl is a favorite with gardeners who want a higher grade covering over their greenhouse that requires little maintenance.

Polycarbonate

Most users agree Polycarbonate is the most durable greenhouse plastic for home gardening greenhouses. Polycarbonate greenhouse covering is 2 layers-thick. Two sheets of polycarbonate are pressed together for twice the thickness and protection from the elements. These layers are also know as twin-walled or a double wall polyethylene plastic. Cost effective but not cheap.

This double wall thickness allows for better heat retention and humidity thus creating a favorable environment for indoor gardening. Its extra sturdy construction means you won’t have to replace this plastic sheeting for at least a decade with a little care.

In Closing

If you’re considering a greenhouse in which to grow your favorite plants, be sure to check out all the options available to you with plastics sheets in lieu of glass panels. Plastic sheeting is less expensive than glass, is easier to maintain and is quickly repairable should the need arise. Another perk is that you can fix small tears and cracks yourself.

There are lots of companies that offer greenhouse plastic coverings to fit nearly any budget or cover any size greenhouse. Naturally, prices vary according to the quality of the plastic and the amount used. If you only have a small greenhouse you can buy a medium grade film that will give your indoor garden all the protection it needs while not requiring you to open a Line-of-Credit at the bank to put up.

Some suppliers even offer a white overwintering film designed for those colder months and also a clear overwintering plastic that allows in a bit more light and heat. There are also standard greenhouse films available online and at many of your local garden centers and nurseries.

​Thanks for reading and good luck!