Is a light change needed to start pre-flower stage?

Hello All,

I am in my first indoor grow.
4’x4’x6’ grow tent. 9 plants in 3 gallon pots.
2x 1200watt greengo LEDs.
Current stage: Veg stage 18/6.
All started from seeds.

I have been looking all over for the answer to this question… Is a light change to 12/12 needed to begin the pre-flower stage?

The results say after 4 weeks of veg the pre-flower stage begins… Should sex the plants… Remove males then on to flowering stage. The articles I find fail to say if the pre-flower is automatically started during the veg stage after 4 weeks or if the switch to 12/12 is necessary.

Further more some say you should not switch to 12/12 until the plant shows pre-flower to reduce chance of herms.

I am confused and could truly use some advice/guidance.

Please help.


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Preflowers show up when the the plants are sexually mature, usually takes 5-6 weeks to be able to tell, no light schedule change needed.


Preflowers show during the veg stage. If they’re mature enough they’ll flower under 12/12.


Thank you so much… I wanted to make sure… It is amazing how quickly my plants grew in a week with all conditions controlled… My LEDs are doing great. Didn’t want to miss the sexing of them and had always thought the light change was necessary.

Now I know what to look for…for my other question… When to start the 12/12? When the preflowers show that the plants are sexually mature.

You are awesome… Thank you!

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I’d wait til you see preflowers, throw out the males, veg up the females til they are good size and then flower. I like to veg my plants at least 8 weeks before flowering.


Thank you once more… I had always assumed and was taught the 12/12 was necessary for sexing…

This info will keep me down the correct path.

You are awesome!

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Save the worry, next time get fem seeds. Hurts to spend 2+ months caring for plants that are 80% males. Lost grow time.
Males will show for a week before spewing harvest killing pollen.

That’s the plan… Just not sure of best way to get them… My options… Go to another state (state lines) hoping their dispenseries have seeds, or buying online and shipping.

What’s the best most secure way or site to get them?

UM…you could order from ILGM … second to none.
10+10 WW special is good price fem’d and an easy grow


Thank you I forgot they sold seeds… As well as awesome info.