When planned well, commercial greenhouse combine the benefits of natural light with the advantages of a controlled environment. A quality greenhouse would provide you with year round cultivation, will reduce your energy bill, and will improve your control throughout the stages of the crops development.
Some growers advocate cannabis indoor cultivation, solely depending on artificial lights. This trend may be effective in terms of crops development, but turns to consume too much energy and may prove to be economically inefficient.
Why grow in a greenhouse?
The vegetative stage of cannabis lasts about 60 days, although some growers shorten it even to 3 weeks. This period is the time the plant deepens its roots and expands its foliage. The more volume the plant will accumulate at this stage the more potential yield it will have at the flowering stage. At this time period the cannabis plant needs light. The more the merrier. This is where natural light penetrating through the greenhouse roof is a blessing, and where you utilize your control systems to ensure a stable temperature and humidity conditions.
You want to use a greenhouse covers that transmits very high levels of photosynthetic active radiation (400-700nm) and that provide good light diffusion properties (Haze factor) for better light penetration and scattering. You need that cover material to let near Infra-Red radiation (780nm-2500nm) into the greenhouse, but you also want it to block the returned radiation (Far Infra-Red) and keep that precious energy in. These properties will ensure your plants get the light they require, and the greenhouse will accumulate the energy it needs to maintain a steady temperature.
A good greenhouse with the right cover will retain so much solar energy, that growing during sunny seasons in subtropical climate zones will require the use of ventilation and cooling systems to prevent overheating.
Additional climate control systems (heaters, dehumidifiers, blackout system and artificial lights) and well insulated reflective opaque walls will give you the flexibility to extend or to shorten any of the plants development phases, to plan multiple harvest every year, and to keep your energy consumption low.
The optical properties of your greenhouse cover
Given the right attention, cannabis thrives in a greenhouse, insulated from the open field conditions while enjoying the best light source in our solar system.
Choose a greenhouse covering that diffuses the light. This will not only protect your crops from prying eyes, but will also reduce excessive heat and reduce crops stress, eliminate shadow spots caused by structural elements, and most importantly- improve light penetration into the crops and generate better and more even growth.
Use Opaque sheets for your greenhouse walls, and make sure they provide a reflective surface. You don’t want to lose that bit of light. Make sure the overlaps between the sheets of your covering and walls systems are properly sealed. A good system is supplied with suitable polycarbonate or metal profiles for that purpose.
Which greenhouse covering is best?
In some countries glass still remains the traditional material for greenhouse glazing, in spite its heavy weight, tendency to crack and the high costs of construction. Polyethylene films are the economic option, but they fail to provide the safety and security that a large scale cannabis facility requires. Only with polycarbonate, with its excellent strength to weight ratio, its flexibility and superior optical properties, you can enjoy high light transmission and diffusion, a wide range of insulation values, and reflective opaque versions for the greenhouse walls.
If you know how to use your equipment well, you can take advantage of what nature gives you. Somedays you may open the vents and enjoy cool, dry wind. You will rid the greenhouse of access humidity and condensation. On other days you will have to use artificial dehumidifiers, heaters and other climate control systems. I like to compare our job as modern growers in controlled environments to playing the almighty: LET THERE BE LIGHT!