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Introduction
The Cannabis L. is a botanical genus of the Cannabaceae family that contains annual plants. The plant is native from the Central Asia, however, it is currently cultivated in all regions of the globe, outdoors or indoors.
It comes in 3 main varieties:
_ Cannabis sativa
_ Cannabis indica
_ Cannabis ruderalis
The varieties are listed according to size, habit, growth rate and chemical composition. The height of the plant varies between 60 cm for the smallest varieties to 7 m for the tallest ones. The average is around 3 m with optimal growing conditions.
Source : Jose Luis Sanchez Pereyra
The active substance responsibles for psychoactive effects is the delta-9-Tetra-Hydro-Cannabinol or THC. There is also the Cannabidiol (CBD) – no psychoactive effects -which has sedative, analgesic and antibiotic effects. We can also mention the Cannabinol (CBN) and the Cannabigerol (CBG) . The cannabis is coveted for its medicinal and recreational properties due to the presence of these different molecules.
Growing cannabis under greenhouses
There are different ways to grow cannabis under greenhouses using low or high-tech model with more automation and equipment. In the article, we will describe both growing system with examples.
Low-tech greenhouses
Low-tech greenhouses generally have less volume, less equipment / automation with more manpower inside. This model has the advantage of being less expensive (greenhouse cost) and easier to implement. Climate control will be limited with less flexibility to reduce insect and pest attack using biological control methods. Indeed, structures are less hermetic and generally have a fixed or manual ventilation.
The yields and the quality of the crop will be more dependent on the outside climate. However, low-tech greenhouses require less energy which improves the profitability of this system.
As an example, we can mention the cannabis production in Colombia using low-tech greenhouse with open-air sides and fixed roof ventilation. The plastic film protects the crops from the rainfall, inside the greenhouse low-pressure sprinklers and circulation fans are used to control the relative humidity %, temperature and air recycling.
The lower cost of the manpower, the rich and fertile soil and the high-lands climate of Colombia explained the presence of foreign companies investing in low-tech greenhouses to grow quality cannabis for pharmaceutical purpose.
High-tech greenhouses
In the other hand, farmers are growing cannabis using fully equipped greenhouse more particularly in the North America. It looks like “hyper-mechanised” factory plants rather than transparent and open greenhouses. All functions of the greenhouse are centralised and managed using modern climate control technology which allows to accurately monitor and change the parameters such as T°C, HR%, CO2%, PAR… inside the greenhouses.
Hi-tech factory greenhouse models using the following technical specifications:
- Wider span ;
- Semi-rigid cladding and roof covered with PVC and/or polycarbonate ;
- Black-out system and shading screens ;
- LED lighting with specific spectrum to grow cannabis ;
- Heating hot air with propane gas (high power) / water heating systems ;
- Cooling system ;
- Dehumidifcation ;
- Active air circulation using powerful blowers and extractors ;
- Passive natural ventilation with motorised vents and roll-up :
- Accurate climate computer with remote control (computer/smartphone) ;
The objective of this cultivating model is to be more efficient using less workers and latest technology. The market price and the cost of the energy are a key factors which will determine the profitability of this system.
Conclusion
In summary, the cannabis market is currently evolving quickly. Two models seems to stand out from the rest : low-tech / hi-tech greenhouses.
The selection of the growing media pots at each stage strongly conditions the cultivation system, possibly mechanised, then the general organisation of the growing phases. It goes from the 5 cm square to the 10 L pot or bag. The tall crops are partially trellised, with a horizontal wire and 2 V-shaped wires taken on the tie-beam to guide the stems. However, the plants can be placed on the ground, directly or indirectly : gutters placed on the ground, small portal frame, benches…
What is more, the ferti-irrigation depends directly on the size/type of containers. In fact, cannabis requires a lot of water, but the plants fear a relative humidity excess in the air. The percolation rates (drainage) is bigger on culture bags for example.
Sources:
https://www.lepoint.fr/monde/colombie-nouvel-eldorado-de-l-or-vert-17-01-2019-2286708_24.php (French)
https://dutch-passion.blog/growing-cannabis-in-a-greenhouse/
https://sensiseeds.com/en/blog/growing-cannabis-in-greenhouses/
