Growing cannabis in greenhouses

Photomontage of two greenhouses with flowering cannabis plants under a clear blue sky. On the left, a small greenhouse seen from the side, with a flexible roof; on the right, a larger glasshouse, seen from the front, with a rigid roof.

Growing cannabis in greenhouses is the way of the future! This is the only way to combine the benefits of both outdoor and indoor growing. Cultivation is safer, more reliable and simpler than in the open air. You also save a lot of energy, which is good for your wallet as well as the environment.

The media regularly reports on raids in the cannabis scene. These reports usually concern commercially run indoor plantations intercepted by the police. We can thank prohibition that when we think of cannabis today it is linked to suspicious warehouses and energy-guzzling lighting.

There is, however, not a single lamp in the world that can compete with the power of the sun. In just one hour, 430 trillion joules of solar energy hits the earth. Just to be clear: That is 430 with 18 zeroes behind it. In theory, that’s enough to meet global energy needs for a whole year.

A greenhouse makes use this natural sunlight, which is superior to any lamp in terms of light intensity and light spectrum. No wonder that greenhouses are booming – from California to Israel, growers are backing this sustainable form of cannabis cultivation.

No life without the greenhouse effect

The atmosphere consists primarily of oxygen, nitrogen and argon, which are also described as greenhouse gases. They act as the earth’s protective shield and ensure stable, life-supporting temperatures.

A greenhouse works in exactly the same way: Light enters through the glass window and is stored in the form of heat. The terms ‘hothouse’ and ‘glasshouse’ are also used as synonyms.

The benefits of a greenhouse

Indoor shot of a huge greenhouse with flowering cannabis plants. Along the centre of the greenhouse there is a walkway, at each end of which there are fans.

If you want to grow cannabis, you need one thing above anything else: light. Lots and lots of light. And what better to provide it than a greenhouse with a transparent roof? The greenhouse effect ensures stable temperatures.

Cannabis likes it warm, but not too hot. Ideally, the temperature in a greenhouse should be between 21 and 25 degrees Celsius. Because a greenhouse can heat up very quickly, a ventilation system with one or more fans is recommended. Additional lights and heaters can be installed at the same time.

The flexible microclimate of a greenhouse offers multiple benefits: It allows the grower to intervene in the cannabis lifecycle and, for example, extend the vegetation phase. Cannabis can be planted earlier and harvested later. Theoretically, several harvests per year are possible – a benefit that is typically associated with growing indoors. In contrast to a grow room, however, the energy costs remain low.

A greenhouse not only provides protection from wind and poor weather, but also from burglars, thieves and vermin.

The disadvantages of a greenhouse

Close-up of a rainy window-pane with raindrops running down it.

If you want to grow cannabis in a greenhouse, you need enough space and a suitable location available. Ideally you want somewhere facing south or west.

A simple greenhouse does not cost much, but if you want to exploit the benefits of a microclimate, generally you will need additional lights, heating and a suitable blackout system. If you also want all these functions to be automated, then the costs can soon reach the same level as indoor growing.

Unwanted odours can be a problem. Active carbon filters can provide a solution, combined with fans. But in contrast to indoor growing, their effect is limited.

Tips for growing cannabis in a greenhouse

Whether indoors, outdoors or in a greenhouse: high quality seeds are a must! They are the starting point of any successful cultivation.

In principle, you can grow any variety of cannabis in a greenhouse. Even late-flowering Sativas, which tend to become mouldy in cold, wet Europe, will thrive wonderfully. Protected from the wind and the rain, they have enough time to reach full bloom. Remember that some Sativa varieties grow very tall, so the greenhouse will need to provide enough space. If that is not available, then the more robust, bushier Indicas might be a better choice.

They are also easier to hide between other plants; tomatoes, for example, are perfect for this. Here is another tip for anyone who wants to keep their growing away from prying eyes: Use white shading paint. It will also protect the plants from excessive heat. More modern polycarbonate greenhouses are not transparent, in which case no whitewash is necessary.

Plants in pots need regular watering and feeding. If they are growing directly in the soil, then the cost of caring for them can be kept to a minimum. In either case, the soil needs to be replaced each year.

Hydroculture is also possible in greenhouses, but is really only suitable for experienced or commercial growers.

Greenhouses require regular cleaning, otherwise diseases and vermin may establish themselves here too.

Which greenhouse is best?

From home-assembly constructions to a fully-automated glass palace – there is a greenhouse to suit every budget. There are basically three different types:

  1. A greenhouse extension is attached to a house, garage or wall. It does not need much space, and can also be used as a conservatory if required. Because it is an extension to an existing building, the cost of the materials remains low.
  2. If you have enough space available, you could consider a free-standing greenhouse. It’s fairly easy to erect a suitable construction made from wood, plastic or metal strips, and then cover in a transparent material. Ready-to-go greenhouses are of course also available to buy. They are delivered in sections and usually consist of profiles made from wood or powder-coated metal.
  3. At the commercial level, there are connected greenhouses. Generally a separate space is created for each phase in the plant’s life. Automated systems ensure optimum watering and feeding.

From the shadows into the light

Prohibition drove cultivation indoors but more recently, cannabis has found its place in the sun. Even today, a large part of the cannabis consumed in Europe and North America comes from greenhouses.

Greenhouses represent the cheapest, most efficient and most environmentally friendly option for producing consistently high-quality cannabis. This benefits not only commercial operations, but cannabis patients and recreational users too. One thing seems certain: cannabis from greenhouses is the way of the future!

  • Disclaimer:
    Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.

Comments

13 thoughts on “Growing cannabis in greenhouses”

  1. Hi Guys,

    I’m looking at materials to build a greenhouse for this years grow. It seems one of the most common materials used for cannabis is the 200micron PE film but depending on the grade of the film used it can reduce light penetration to between 77&91%. Will a loss of up to 23% light penetration greatly affect yield?

    1. Scarlet Palmer - Sensi Seeds

      Hi Jason,

      Thanks for your comment and question. Unfortunately, I cannot give you a definite answer as this is outside my experience – I would guess that you will have a slight reduction in yield, but there are other factors that can influence a greenhouse grow (compared to an outdoor grow) that might compensate for it.

      Our other readers will often weigh in on questions like this, so you might be able to get feedback from someone who has tried this. Good luck, and happy gardening!

      With best wishes,

      Scarlet

      Hopefully

  2. Cid wouters

    Dear Sensi seeds

    Do you guys think white washing the greenhouse roof and sides will reduce the yield in a drastic way?

    Friendly regards

    1. Scarlet Palmer - Sensi Seeds

      Hi Cid,

      For legal reasons, we can’t answer direct questions about growing on this blog. However, other readers will often contribute their experience and knowledge to help answer questions like yours. I can tell you that the more light plants get, the happier they are, but they are also capable of growing in less-than-perfect conditions. Good luck!

      With best wishes,

      Scarlet

  3. I’m in a state that it’s not legal in any form yet. suggestions on an underground green house with clear roof. at its tallest point will be 3ft angled towards the west down to 1 foot. but goes 4 ft in the ground. looking for suggestions just trying to keep the ditch weed growing everywhere to not pollinate my plant

    1. Scarlet Palmer - Sensi Seeds

      Hi Aaron,

      Unfortunately, legal restrictions mean we can’t answer grow-related questions or give grow advice on this blog. However, we do have the Sensi Seeds Forum where you can browse through questions and share the experiences of a community of cannabis and gardening enthusiasts.

      Also, other readers of this blog will often answer questions like yours. Sorry I can’t be of more help, and I hope you continue to enjoy the blog!

      With best wishes,

      Scarlet

  4. Does some greenhouse glass block uv light,resulting in a lack of potency,when flowering.

    1. Scarlet Palmer - Sensi Seeds

      Hi Dave,

      Thanks for your comment and question. There are some types of glass which are specially made to block UV rays, but greenhouse glass is not usually one of them because all plants rely on light for growth so it would be counterproductive to use glass that blocks light. Ultraviolet waves, infrared light waves, and visible light waves – which are the three types of light produced by the sun – all pass through standard glass.

      I hope this answers your question, and that you continue to enjoy the blog.

      With best wishes,

      Scarlet

      1. Mitchell Williams

        Ok if I buy a green house and it says UV protected. Will the right amount of sunlight get through or does any get through????? And can you grow cannabis

      2. Scarlet Palmer - Sensi Seeds

        Hi Mitchell,

        Presumably your greenhouse is designed for standard gardening, in which case it should be fine for growing cannabis. Is it made of plastic? Plastic is photo-degradable, so if it says ‘UV protected’, this is probably to prevent the plastic from becoming weak and brittle when exposed to sunlight for long periods of time. I hope this information answers your question.

        With best wishes,

        Scarlet

  5. Grass Chief

    A greenhouse is superior to grow cannabis because it is better than any lamp in terms of light intensity and light spectrum. It uses natural sunlight which is a renewable energy. A fabulous post with lots of incomparable ideas.

  6. Frederick Monaghan

    All your pictures above are of `polytunnels` covered in plastic.
    At horticultural college, they taught me that glass is better than plastic because the plastic cuts out some of the light spectrum.

    1. Olivier - Sensi Seeds

      Hi Frederick, thanks a lot for your input. I was not aware that transparent plastic cuts out some of the light. All the best, Olivier

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    The Sensi Seeds Editorial team has been built throughout our more than 30 years of existence. Our writers and editors include botanists, medical and legal experts as well as renown activists the world over including Lester Grinspoon, Micha Knodt, Robert Connell Clarke, Maurice Veldman, Sebastian Maríncolo, James Burton and Seshata.
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