There are many options available for a polytunnel cover material. These can differ in flexibility, resistance, durability, and especially price. It should be remembered that the cover applied onto the frame is the most important factor impacting plant growth. It affects air and soil temperature as well as humidity inside. A poorly sealed structure will allow the heat accumulated inside to escape from the tunnel. As for all year round production, the cost of heating will be much higher during cold months . On the other hand, if it is too tight, the temperature will rise quickly, meaning you will have to ventilate more often. Of course, both cases are extremes. However, even a small element affects working conditions and the environment in which vegetables and fruits will mature.
Contents
Types of cover for garden constructions
Foil tunnel with polyethylene film
The film is made of plastic, with optimal light diffusion. It is used both in small polytunnels for hobby cultivation and professional vegetable and fruit production. Thanks to a low price, it is entirely or partially replaced if a particular segment has been damaged. Special tapes are used for repair work, but this is only a temporary solution to the problem.
Foil sheets are applied onto the frame, pulled with a string, laid following arches or installed straight onto the structure. The foils strips are secured by latches or clips. In the case of hobby foil tunnels, the tunnel is mounted by the customer, for multi-bay or multi chapel units, by a company or employees of a given manufacturer. The installation of a foil cover is very simple, following the tunnel assembly instructions is just required. Most of these greenhouses are seasonal structures, which can be fitted with heating systems to be suited for all year round cultivation.
Pros:
- Cheap
- Easy to assemble, disassemble and easy to store.
- It provides good diffusion of light.
- Protects against frost.
Disadvantages:
- Place the structure away from trees and shrubs and handle it carefully.
- Difficult to clean, a much more reasonable and cost-effective way is to replace it.
Fiberglass foil tunnel
Much more expensive than foil, however more durable and equally effective. They have similar light-collecting properties, but in the case of fiberglass, the material becomes completely transparent over time, and the diffusion of light is significantly affected. This fading process, whose first visible phenomenon is a yellowish taint, begins after one year. Glass fiber is more often used for shelters and roofs than for horticultural constructions, as the level of light transmittance is 73% in the highest range .
Pros:
- Good light diffusion when the product is new.
- A durable cover
- Permanent, though less effective over time
Disadvantages:
After several seasons, and sometimes after the first one, if the material is of low quality, the fiber glass shrinks and the material gets rough. Then it becomes more susceptible to dirt and requires thorough disinfection.
Characterized by low heat retention inside the tunnel.
Polycarbonate tunnel
Solid, stiff material with good light transmission and insulation. The whole assembly of a polycarbonate tunnel is much more difficult. It requires matching the slabs, cut into pieces, onto the structure. Be careful not to bend the panel too much, as it may break. Although it is a cover with good features, it is the least modifiable. It will be difficult to extend the greenhouse with additional segments without purchasing them directly from the manufacturer. Therefore, before deciding to opt for such a cover, we recommend checking if additional elements are available separately. For this reason, all non-standard constructions are available only on request.
Pros:
- Attractive appearance
- Durable
- It insulates heat well
Disadvantages:
- Spreading of light not optimal with dark patches appearing inside, so crops grow uneven and the plants compete with each other for access to light.
- Prone to scratches
- It breaks if the pressure is too big
- Not a cheap materials
Greenhouse with glass cover
Glass is chosen because of its aesthetics qualities, unfortunately it is a very expensive material. Low-quality material is prone to damage when used at production stage and the durability of such panels is quite low. The structure gets too hot without shading screens, even with proper air circulation, it also takes a long time to release excess heat. Installation is quite difficult, so we recommend that you hire professionals. This, in turn, involves additional fees. It is not possible to move such a greenhouse to a different location, as it is the case with the other types, so the chosen area will be final.
Pros:
- It looks beautiful
- Perfect for professionals
- Good heat retention
Disadvantages:
- Prone to damage
- Not for amateurs and beginners
- It does not deflect light
- Very expensive material
Which material for the professional polytunnel, and how about the hobby tunnel?
To a large extent, it depends on the financial resources available for the construction. It is difficult to determine which one is the most effective. Each material has its advantages and disadvantages. It is important that design allows the gardener to change the cover without any hassle. In the event of damage, one must be able to repair such a defect right away.
What not to buy?
It is much easier to determine what materials not to buy. This certainly applies to cheap green foil tunnels. Such a cover supplies only from 32 to a maximum of 54% of light, whereas light diffusion is barely non existent. The cover itself creates a number of dark areas meaning plants are fighting for every ray of light inside the structure. With only 32% of the accumulated heat going through, all the rest is reflected or ends up on the top of the cover which has a low level of thermal insulation. However, the difference is that plants suddenly get cold rather than gradually. This may lead to their wilting, dwarfing, and in the worst case – death.
Other factors worth mentioning is that green covers in those foil tunnels can burn and melt on the structures. They are treated with chemical preservatives that are released during cultivation. Winds and the smallest amount of snow can damage them, while hail can create holes.
Although this may seem exaggerated , the difference in the material between the very cheap foil tunnels and a solid foil tunnel is clear to see. The first type of construction is a one or two-season structure at best, the latter will be used for many many years.