How Good Are Polycarbonate Greenhouses? Are They Really Worth Buying?

By Paul Smart •  Updated: 06/20/21 •  6 min read

How Good Are Polycarbonate Greenhouses? If you are someone that really loves to garden, having a greenhouse is something that most gardeners aspire to have in their back garden. However, if you start to look around at the cost of some of those beautiful greenhouses you see on television shows like gardener’s world you may get a bit of a shock.

A high-quality glass greenhouse can set you back several thousand dollars, which for most gardeners, including myself is a cost that I find hard to justify. The alternative is to purchase an aluminum-framed polycarbonate greenhouse which costs a few hundred dollars, which is what I did. So was it a good purchase or not?

Polycarbonate greenhouse for me was an item that was worth purchasing as it gave me the ability to grow masses of seedlings in my own greenhouse at a low cost but you definitely get what you pay for. These types of greenhouse do work well but they need modification to ensure that are able to withstand the worst of the winter weather.

The problem with the design of these types of greenhouses is that polycarbonate panels slot into grooves in the aluminum frames but they have no screws for fasteners to hold them in place. This makes them extremely cheap to produce and easy to put together but when exposed to prolonged high winds the large panels tend to flex inward. This flexing is sufficient to push the panels out of the grooves.

Once the panels are out of the grooves they either get completely removed or the panel gets damaged. In my experience, this only happens on the side and roof panels because they longer. This increases the chances of the panel bowing. The photographs of my greenhouse after a winter storm show that smaller end panels around the doors remain intact whereas the longer panels are more susceptible to damage.

The result of winter storms and not enough reinforcement

How To Reinforce A Polycarbonate Greenhouse

When purchasing a polycarbonate greenhouse it is best to put the reinforcement in place immediately to avoid damage rather than have to deal with it at the most inopportune moment. ie in the middle of the storm

There are two methods I have used to reinforce the panels. The first method, which is the easiest is using tape, which will last a season or two but will require reapplication periodically due to the disintegration of the tape over time or the loss of adhesion. The quality of the tape used will determine the period of time it lasts.

The best tape I have found is fiber-glass reinforced tape which is stronger than the ordinary packing tape and will last a lot longer. The type of tape I have used is available on Amazon, click here to see the latest price.

When applying the tape it is generally only necessary to apply it to one or two strips across the center are areas of the largest panels. The tape should be applied perpendicular to the grain of the panel, which for most greenhouse means the tape needs to applied in the horizontal direction.

It easiest to apply the tape in a single strip across the length of the greenhouse. As the tape is applied, it is important to ensure that every section makes good contact with each panel to ensure a strong bond is formed. Additionally, the tape should applied to both sides of the panels for maximum strength.

The second method, which is a longer-term solution, is to screw reinforced timber rods along the sides and roof of the greenhouse. This is best applied by screwing the timber into the frame of the greenhouse at either end on the inside and out. The timber can then be joined together by drilling through the timber and polycarbonate sheet to the other. The two pieces of timber can then be joined together with a nut and bolt.

To minimize the movement of the panels it will necessary to have a third piece of timber between the main pieces to ensure that the timber butted up against polycarbonate on both sides.

If you chose to use this method it is important to use hardwood timber and paint it prior to attaching it to the greenhouse to maximize the life of the reinforcement. Secondly, always have the nut on the inside of the greenhouse to avoid rust so that the timbers can be removed and replaced as required.

What Size Greenhouse Should I Purchase?

The size of greenhouse that most people purchase is either 6′ x 4′, 6′ x 6′ or 6′ x 8′ greenhouse. I personally would recommend a 6′ x 8′ greenhouse, which the size I have, for a couple of reasons. The first is that if you are going to bother putting one in it is better to get the larger size, as it provides maximum flexibility in the future.

The second reason is that have greenhouse can be used to stagger the harvest date of crops by splitting seedlings into those planted outdoors and those planted in the greenhouse. I personally devote around half my greenhouse space to producing crops and the other half to producing seedlings for the garden.

The third reason is that having a greenhouse that is larger reduces the degree of fluctuation in the temperature within the greenhouse. Smaller greenhouses tend to heat up in warm conditions much more quickly.

How Long Does It Take To Erect A Polycarbonate Greenhouse

Polycarbonate greenhouses are relatively easy too erect, however, it is much easier and faster to erect them with 2 people. Typically, they can be erected in a half a day to a day, and only require an alum key, a screwdriver, and sometimes a spanner.

However, it is advisable to wait until there is a still day as a windy day makes it extremely difficult and it increases the likelihood of panel damage.

Are Polycarbonate Greenhouse Easy Top Repair

Polycarbonate greenhouses are extremely easy to repair. As mention earlier in the article the main thing that can go wrong with them is damage to the panels. A new panel can generally be purchased from the local hardware store. They are can be easily cut to size using a knife. The biggest hassle is removing the additional reinforcement to put the new panel in.


Polycarbonate greenhouses are in reality relatively flimsy structures that can be damaged easily in storms. However, if you spend the time reinforcing the panels adequately they provide a relatively low cost alternative to glass greenhouse.

I personally think that if you have a large garden they are really worth having and they are far superior to the mini greenhouse that can be purchased. Just don’t do what I did which is erect on the assumption it will be ok as is. Good luck with whatever you decide to do.

Paul Smart