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When to Flip From Veg to Flower

Many new growers struggle with the dilemma when they should flip their plants from veg to flower. Unfortunately, there is no concrete answer to this, but instead depends on a variety of different factors. Want to know when the perfect time to flip is for your garden? Become an expert & learn it here!

Some say that the key to life is divine timing – but I won’t claim to know the answer for life. As for growing marijuana, it’s one of the most important factors.

It’s essential to know when: when to be light, when to be dark, when to water, harvest and of course, when to flip from veg to flower. It is extremely common for new growers to wonder when it is time to induce the flowering stage for their cannabis plants, and most of the information available is vague.

There is no strict rule on when to switch your plants from the vegetation stage to the flowering stage and it will depend on a lot of different factors, such as the amount of time and space you have to work with. The amount of time the plant spends in vegetation will also depend on the strain and whether you are growing from seed or clone.

In this case, copying another grower’s timing schedule won’t be of any use, unless they are growing the same strain in the same setup and with the same amount of space. To know when to flip from veg to flower, the grower should consider all the factors that are specific to their growing setup.

This article is a comprehensive guide to the basics of timing. With all the information covered here, you should know enough to be able to make an informed decision about the perfect switch time for your cannabis plants.

What does it mean to flip?

To start with, before you go flipping, you should remove all the male plants from your garden (but don’t throw them away!). If they are left with the female plants during flowering, you will end up with seeds instead of buds. So, what does it mean exactly to flip from veg to flower?

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An indoor grower’s task is to successfully mimic the elements indoors. So, flipping is a way to tell the plants that the seasons are changing by increasing the number of hours they spend in the dark. More specifically, this means changing the light/dark cycle from 18/6 to 12/12.

Female plants will not begin to develop buds until they enter the flowering stage. This means that the moment you switch the light/dark cycle, plants will stop sending energy into root development and start sending it into flower development.

Autoflower 12/12 Light Cycle

Autoflowering plants as we have determined earlier grow best when you give them between 18 and 24 hours of light each day but there are many circumstances when a grower need to give his plants only 12 hours of light. And today I will try to explain the what, why and when about autoflowers and 12/12 (day/night) light cycle.

First of all I need to say that you can absolutely grow autoflowers on a 12/12 light schedule and they will produce great buds but because those plants will receive less light then their yield will be smaller than if you compare them with plants that are grown under 20/4 or even 24/0 light cycle.

Why use 12 hour light cycle?

There are many reasons why a grower would grow autoflowers under 12 hours even if autoflower plants do best under 18 to 24 hours of light. And here are the most common reasons:

  • Autoflowers in the “flower room” – If you are growing regular (photo-sensitive) plants but still want to get some early autoflower buds then you can put autoflower seeds in the flowering chamber and get decent buds well before your photo-sensitive strains have matured. You can even grow your autos together with photos from the start giving them 24 hours of light and then switching the light cycle to 12/12 when you want your photos to start flowering. Autoflowers will not mind the light cycle change and contrary to popular belief this change won’t increase the hermaphrodite rates.
  • Growing autos outdoors – If you are growing autoflower plants outdoors in the spring or in the autumn when the day is about 12 hours long then that won’t impair autoflower plant growth and they will still flower and produce you great buds.
  • Too hot temperatures during the daytime – If you are living in a climate where the summers get really hot then you might want to only turn on your grow lights in the night when the sun is down and the ambient air gets cooler. In this situation you can still get some indoor autoflower buds even with 12 hours of light that turns on only in the nighttime.
  • Cutting electricity costs – If you are on a tight budget then you can reduce the light cycle from 24 to 12 hours and cut your electricity costs in half but still get some decent buds. But be careful because some autoflower strains will take longer to mature when grown under 12 hours so your savings may end up eroding due to longer grow time and less yield.
  • Bad genetics – If your “autoflower” plant does not automatically flower under continuous light cycle after 3 to 6 week then you might have a bad batch of seeds and you will need to manually adjust the light cycle to 12/12 and kickstart the flowering phase.
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As you can see then there are quite a few reasons when you might need to grow autos under 12 hours of light but this practice also has some drawback.


  • Increased stretching – If you give your autos only 12 hours of light each day and 12 hours of darkness then that can promote some unwanted and excessive stretching so you need to get your autoflower as close to the light source as you possibly can when those lights are on. And you should also give them complete darkness in the night-time so that the plant doesn’t try to stretch to the light that leaks in your grow room trough some openings.
  • Slower growth – If you give your plants less light they will grow slower and won’t produce as many new branches and leaves so you will end up with a smaller plant and less leaves / branches and fluffier buds.
    Longer growing cycle – Some autoflower strains will take longer to mature if you give them only 12 hours of light. And I have seen plants that need more than 30% longer growth time to get to the harvest stage when grown under 12/12.
  • Less yield – And ultimately when you are giving your plants less light then they will give you less yield and that can be a big drawback to many growers. But sometimes 12/12 is your only choice and even with less yield from a single plant you are still getting at least some buds and you can also grow more plants to compensate this decreased yield.
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So the most popular light cycles for autoflowering plants are growing under 12/12 from the start or switching from 24/0 to 12/12 when the autoflower flowering phase starts.

  • 12/12 from the start – If you are growing autoflowers in your flowering room then you can grow them from start to finish under 12/12 light/dark cycle but that will produce the worst results as your plants will get the least amount of light.
  • 24/0 then switching to 12/12 – The best option if you want to use the 12 hour days is to start your plants under 24/0 or 18/6 while they are in their vegetative growth stage and then switch that light cycle to 12/12 when the first pre-flowers appear. This will give your autos the most amount of growth and the yield will not suffer that much.

And there are also some more exotic light schedules like 14/10, 14/8 13/11 (light/dark) that are used of regular photo-sensitive plants and where autoflower have been grown. But I do not see the advantage in these schedules as they don’t produce more buds or if they do then the difference is usually miniscule.

And now you can make an educated decision if you want to grow your autoflowers under 12/12 or better wait and grow them under 18/6 or 24/0 light cycle.