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Benefits of hemp cultivation under greenhouses – high tunnel type

Intensive hemp production under plastic greenhouse

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Introduction

Industrial hemp(Cannabis sativa L.) has been cultivated for many years in the world. The plant has been used to make ropes, sails and clothing. Indeed,hemp fibers, found on the outside of the hemp stalk, are the most resistant natural plant fiber.

Hemp is also cultivated for itsinflorescencewhich can containcannabinoids(THC, CBD, etc.). Industrial hemp contains only about 0.3% – 1.5% THC (under 0,3%THClegally in Canada and US: check 2018 Farm Bill) while cannabis contains about 5% – 10% or more THC (delta-9-tetrahydrocannabinol). The THC molecule has psychoactive properties when consumed.

However, industrial hemp has higher concentrations ofCannabidiol (CBD). The CBD is a chemical compound from thecannabinoid family. Some studies show thatCBD sourced treatmentsmay help fight anxiety, ease schizophrenia symptoms, epilepsy and reduce pain… all without resulting in too strong side effects (Rock et al., 2011).

Nowadays, there is a growing interest in cultivating hemp forCBD oilandseeds(used in the food industry). The oil is very nutritious and rich in protein as well as omega-3 and omega-6 fatty acids.

Hemp growing conditions

Hemp seedsneed a minimumtemperatureof 1-2°C for germination and emergence. The temperature range for hemp growth is 19-25 °C (66-77 °F). When the average temperature rises to 16°C the plant grows quickly (about 5cm or 2 inches/day).

Both hemp and cannabis crops require avegetative and flowering stageof development. During the flowering phase, the optimal temperature is 16°C (61°F) during night period, and 28°C (80°F) during the day.

Hemp favorsmedium-heavy soilsthat are well irrigated but free from standing water and compaction. The optimal pH is above 6.0, neutral toslightly alkaline(pH 7.0 – 7.5) is preferred.

Hemp is anundemanding cropto grow requiring little more than a fertile and well-drained soil. The plant is robust, botrytis being the main disease that affects it. Young plants are very sensitive to wet soils during the first 3 weeks.

Source : http://www.omafra.gov.on.ca/

Normally,male hempplants are less developed compared tofemale plants(Small, 2017). Below a picture showing hemp inflorescences : male (left) and female (right)

资料来源:小,2017年

Advantages of growing hemp under a high and wide tunnel type

The main challenge and disadvantage ofoutdoor cultivationis the fact of not being preconditioned to yield homogenous hemp produce. Crops will also be more exposed to weather events such as hail, heavy rain…

大麻种植者使用greenhouseswill be able to have one or two additional cycles of cultivation in the year (instead of one in outdoor cultivation). Moreover, it is possible to artificiallyshorten the light exposurein greenhouse production using ablack-out screen systemand therefore induce flowering (12h of darkness) earlier and more often.

Wide and high ground-to-ground tunnelof 12,80m wide x 60m long (or 42′ wide X 200′ long) isan ideal alternative大麻种植者来说,想从空旷的田野farming to a more controlled environment. It offers more parameters and efficiency to produce hemp for its medicinal purposes. Professionals will also say that it is moreaccessible financially(in terms of cost per sqm or sqf) andeasier/quicker to buildthan a gutter connected greenhouse.

The farm manager can operate the被动ventilation(roll-up, roof ventilation manual or motorized) to provide the optimal environment for growing hemp. In fact, growers like lots offoliage movement, it ensures/ assists with minimizing “pooling” of humidity in the canopy. In fact, humidity can cause mold, a big issue with flowering cannabis growers. Air recycling allowscarbon dioxideto enter the greenhouse in the most cost-effective way.Artificial lightingcan be added however you might keep an eye on the electricity bill to stay competitive.

In addition, the growing environment could be more easily in compliance withGood Agricultural Practices (GAP). The usage ofbiocontrol solutionssuch as beneficial insects is also more efficient in a greenhouse covered with PE film and netting on sides.

Sources:

https://www.hempbasics.com/hhusb/hh2cul.htm

http://www.omafra.gov.on.ca/english/crops/facts/00-067.htm

Hemp (Cannabis sativa L.) for Medicinal Purposes: Cultivation under German Growing Conditions, Eva Vogel 2017.

Rock, E. M., Goodwin, J. M., Limebeer, C. L., Breuer, A., Pertwee, R. G., Mechoulam, R., & Parker, L. A. (2011). Interaction between non-psychotropic cannabinoids in marihuana: effect of cannabigerol (CBG) on the anti-nausea or anti-emetic effects of cannabidiol (CBD) in rats and shrews. Psychopharmacology, 215, 505–512. https://doi.org/10.1007/s00213-010-2157-4

Small, E. (2017). Cannabis: a complete guide. CRC Press Taylor & Francis Group.

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Agricultural engineer (MSc) working in the greenhouse and horticulture industry. My international experiences and my knowledge allow me to work with farmers and professionals across the world to advise them.

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