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How to Grow Autoflowering Cannabis Plants in a Greenhouse

  • The start of the outdoor season is an eagerly anticipated moment for many growers, and automatics are, increasingly, the choice of many who have been seduced by their many advantages. Outdoor cultivation, however, is burdened by a small handicap: you have to wait for good weather.
  • What if we told you that you could move your cultivation up a few months? Magic? A lie?
  • No, greenhouses! It's as simple as that.
  • Read on because in this post we will reveal the keys to growing autoflowering plants in a greenhouse, a simple method that offers many advantages.
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Autoflowering plants can be grown both indoors or outdoors, but in the latter case it is essential that there be sun. If the light is not strong enough, autoflowering cannabis strains cannot fully develop, and your harvest will be rather poor. A greenhouse is an excellent choice to move up the cultivation of your autoflowering plants, as in it your cannabis plants can receive the hours of sun they need without suffering the effects of cold and inclement weather. For example:

Imagine a crop located in the Mediterranean, an area with a generally mild and temperate climate, where winters are warmer than in other regions. In April the sun might be enough for automatics to receive the light they need, but be careful! Spring is a very precarious season; though it can feature sunny days portending the summer's arrival, it can also surprise you with torrential rains capable of drowning small and vulnerable cannabis seedlings before they are able to develop.

To grow your automatic strains during these months, we suggest using greenhouses. Want to know the ins and outs of this cultivation method? Read on!

The advantages of growing your autoflowering plants in a greenhouse

  • Protection: a greenhouse prevents plants from getting wet when it rains, and also from dust and birds.
  • Temperature increase: this can be an advantage or a disadvantage. It depends on each case. It is good for cannabis plants to develop in a temperate climate (24-28º), but when it exceeds 30 degrees they can be adversely affected.

Can you move up the cultivation of autoflowering plants by using a greenhouse?

Yes, you can. With a greenhouse it is possible to plant more automatic crops in the course of a given year, as inside it plants are protected from the effects of inclement weather, thanks to which you can move up sowing in the spring, and push it back in the autumn.

How does the greenhouse affect the development of automatics?

As a greenhouse protects plants from rain, you can avoid a common problem when growing autoflowering plants outdoors, as rain on this type of genetic can be deadly; when the soil is wet for too long, the plant's roots become waterlogged and it is rendered stagnant; that is, it does not grow. For an autoflowering plant this blow is decisive, because its short life cycle does not give it time to recover.

Can you grow autoflowering cannabis plants in the winter with this method?

It depends on the climate. If it is a very cold climate, the answer is no. But if, for example, you are growing in a southern Mediterranean region, then yes, you can.

Does the greenhouse's plastic reduce the lumens reaching plants?

Very little. There are many types of plastic, and that normally used in greenhouses is transparent, letting light pass through it without any problem. There are some plastics that are slightly more opaque, used in some greenhouses during the summer, when the sun is too intense.

When and where is a greenhouse the best choice for growing autoflowering plants?

  • Nordic climate: a greenhouse is a good choice for the summer season in regions with colder climates, as they maintain a higher temperature inside and protect plants from inclement weather.
  • Temperate / Mediterranean climate: a greenhouse is very effective for the spring and autumn months.

A greenhouse generally maintains a higher temperature inside than there is outside. Autoflowering plants cultivated in greenhouses grow more and higher. At Dinafem we chose to confirm this through an experiment, planting the same autoflowering strain inside and outside a greenhouse, simultaneously. After two months, the plants that were inside were twice the size of those outside. Why? It's quite simple: inside a greenhouse it's warmer, which means that cells multiply more quickly and tissues grow at a faster rate. And with automatic genetics, the larger the plant, the bigger the harvest, in general.

What disadvantages does growing automatics in a greenhouse feature?

  • Interior temperatures can get too high. Remember that for photosynthesis, at over 28 degrees the plant has to release lots of water in order to cool down. The greater this transpiration, the more photosynthesis is hindered.
  • With very high temperatures there will normally be a lot of humidity, in which case cannabis plants can become mouldy and sparse, and are at risk of botrytis.

In any case, we must stress that it is easier to control moisture levels inside a greenhouse than outdoors, because you can limit the water you give your plants. A well-managed greenhouse is well ventilated; ideally its two doors on each side are opened each morning, thereby renewing the air. Finally, if you decide on this method, here are some tips to ensure a good harvest ...

Tips for growing autoflowering plants in a greenhouse:

  1. Use a large pot (at least 11 litres and 30 litres max.)
  2. If you are planting in loamy soil, make sure the soil is spongy.
  3. Water frequently but in small doses to keep the substrate moist but light.
  4. Limit irrigation during the final phase. Keep the greenhouse as dry as possible during the last month of cultivation.

Comments from our readers

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  1. 5 out of 5

    There are some great tips here, thanks! What is the best compost/soil to use, please? Can you use a multi grow or is it best to splash out on a coco terra?

    1. 5 out of 5


      Thank you for this comment.
      Unfortunately, we cannot recommend any particular brand or type of soil.
      In the end, it all comes down to the grower's preference, and his personnal experience with the substrate.
      Usually, the best soils are a mix of different substrate (coco, perlite, ...) allowing the roots to develop properly without drying out or suffering from water retention, and therefore mold.

      Best regards
      Dinafem Seeds

  2. 5 out of 5
    Very helpful
  3. 5 out of 5
    How does this work out in places that get 12 hours of light year round?
    1. 5 out of 5
      You can do it, as autoflowering genetics don't depend on the photoperiod and start flowering in the third week. But the final yield will be lower.

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