Growing in greenhouses is certainly the best way to start the urban farming season earlier and extend it late in the fall. Without using a heating system, this type of greenhouse makes it possible to start the season in early March and extend it until December, sometimes even in early January.
Many models of small home greenhouses are sold online, as well as in garden centers and supermarkets. Usually made from an aluminum frame and covered with polycarbonate or polyethylene, most of these greenhouses are affordable, lightweight and easy to assemble yourself. As for glass greenhouses, these are significantly more expensive, require a foundation and their installation should generally be entrusted to professionals.
On the other hand, a cheap method is to grow vegetables under tunnels covered with plastic wrap. Such a tunnel actually consists of a thin transparent polyethylene film installed in a simple structure made of flexible plastic or steel rods placed in arches.
The polyethylene film allows sunlight to pass through and retains enough heat at night so that some edible plants can grow during the cold days of late winter. The soil absorbs heat during the day and re-emits it at night in the form of infrared radiation, thus helping to keep the air under the plastic wrap warm enough to prevent plants from being affected by the cold. You can also install a ground heating cable to ensure the integrity of the vegetable plants during colder periods.
The size of a greenhouse depends on the budget, the amount of plants you want to grow and the size of the soil on which you want to install it. However, do not think too small, as to be able to work comfortably in a greenhouse, it must be at least 2 to 2.50 meters wide and a height of at least 2 meters from the ground to the roof, so that he can stay there. The height of the walls is also important and should be sufficient to allow easy access to the plants grown at the edges.
The ideal location for a greenhouse is a sunny spot, overlooking the south. It can be very helpful to support your greenhouse against a dense evergreen hedge on the northwest side to protect it from cold winds.
Above all, do not forget to check with your municipal authorities for regulations regarding the construction and installation of home greenhouses. Some cities encourage the practice of urban agriculture, but some do not allow the establishment of permanent greenhouses in their territory.
A small greenhouse, the structure of which is made of steel or aluminum, can be placed in the ground, if you want to grow vegetable plants in the ground, or directly in the cover of a terrace or a yard, in case the culture is done in a container .
Alternatively, if a greenhouse is installed on clay soil that is subject to movement during freezing and thawing cycles, it may be necessary to place the pillars supporting the structure on a compacted gravel foundation at least 30 cm thick to prevent displacement. her. or deforming.
For their part, wooden greenhouses should ideally be placed in a gravel bed to prevent them from coming into contact with the soil and thus prevent their decomposition by microorganisms.
Finally, if the covering material of a greenhouse is glass, it should definitely be placed on pillars or on a concrete foundation.
As it ensures the strength and durability of the greenhouse, the structure is an important element to consider. Several materials are available, the most common of which are steel, aluminum and wood.
Since steel has great strength, it allows the production of fine structures thus ensuring maximum penetration of sunlight. On the other hand, steel rusts when exposed to air and water. Thus, it is preferable to choose galvanized steel, i.e. covered with a layer of zinc that protects it from corrosion. On the other hand, some manufacturers cover steel structures with a highly weather-resistant baked paint. Steel is most often used with coatings made from plastic films.
Aluminum structures are generally lightweight, easy to assemble and require little maintenance as they do not rust. For all its convenience, the aluminum is solid, which allows for the production of fine structures and the use of larger polishes. In addition, polishing or polycarbonate panels can be easily inserted into an aluminum structure and held in place using clamps, rubber seals or simply interlocking.
Since aluminum tends to stain and heat up over time, some manufacturers offer anodized aluminum structures (silver, bronze, or black), or coated with baked paint as in the case of steel. Thanks to its many qualities, aluminum is undoubtedly the most used material for the production of small greenhouses for amateur gardeners.
Wood is generally a less expensive material than steel and aluminum for the production of greenhouse structures, but on the other hand, since it is a living material, it has a tendency to deform under the effect of moisture cycles and freeze-thaw. . In addition, the wooden structures of greenhouses are generally heavy and bulky, which makes them more difficult to mount and reduces the amount of light that can penetrate them. Wood also requires regular maintenance to prevent it from being affected by mold and rot.
Eastern or western nail, commonly known as cedar, is an excellent choice as it is relatively durable and does not need any treatment as it is naturally resistant to rot. Larch is another rot-resistant and weather-resistant species that is little known. Larshi allows the construction of greenhouses less costly and resilient.
To grow and develop optimally, edible plants need light and heat. Of course, the material covering a greenhouse should be transparent, even translucent, to allow as much sunlight as possible. The cover material also has the function of protecting plants from bad weather and reducing the effect of cold outside on the indoor atmosphere. There are several materials, the most common of which are plastic films, polycarbonate and glass.
Plastic films are usually made of polyethylene, a relatively cheap substance made from petroleum. Coated to capture a layer of air, these plastics offer good protection against cold winds. However, they should be replaced regularly, approximately every five years. In addition, the sun’s UV rays degrade the plastic surface, which can darken it if left untreated, thus reducing the amount and quality of light captured.
Maintaining a plastic greenhouse cover is easy; this includes washing it annually with warm soapy water. To extend the life of a plastic film, it is recommended to adjust it well in the structure. Under the influence of wind, a poorly stretched plastic cover will tend to rub and therefore deteriorate faster.
Polycarbonate is a plastic material made from petroleum – the production of which unfortunately emits greenhouse gases such as polyethylene – which is generally sold in the form of solid slabs composed of walls separated by cavities in which air is trapped. The lifespan of most types of polycarbonate is more than ten years.
Single-walled polycarbonate is almost as transparent as glass, but significantly more shock-resistant than glass. Simple polycarbonate panels are lightweight and easy to install, but they have poor insulating power. For example, a single 0.75 mm thick polycarbonate sheet has a thermal resistance of only R1.
There is also two- or three-walled polycarbonate, also called alveolar polycarbonate, offering better insulating power. For example, a 10 mm thick double-walled polycarbonate has a thermal resistance of R2, while allowing slightly more than 75% of sunlight to pass through. Double-walled polycarbonate panels retain approximately 40% more heat than single-walled polycarbonate. In addition, dual polycarbonate reduces the occurrence of burns due to periods of strong sunlight by stopping almost all UV rays.
Probably one of the most transparent materials in existence, glass is the most suitable material for building greenhouses, but it is also the most expensive. Since it is heavy and fragile, it is also better to entrust its installation to professionals. The glass allows 90% of sunlight while blocking a lot of UV rays.
Glass also has a low insulating power. That is why it is preferable to choose double or triple glass with energy efficiency, the interstices of which are filled with argon, an inert gas. For example, triple glazing sealed with argon and covered with a low-emission film has a thermal resistance of R6.5. In addition, tempered glass is stronger, reducing the risk of breakage. When broken, it breaks into small, clean pieces.