is it safe to flip to 12/12 a few days to help show sex

I have 3 girls 6 weeks since germination. Will flipping them to flower for a few days be detrimental to them?

For planning & space purposes i need to know how many girls i have.

Any thoughts?

I would try your best to figure out the sex by looking at the preflowers. If you aren't able to do that, take a clone and flower it to see it's sex as it will be the same as its mother's. You can put them into flower for a week and then go back, it does stress the plant though and irregular light patterns can cause hermies.

Heres a guide with helpful pics here on RIU: https://www.rollitup.org/t/sexing.340683/

Basically if the preflowers are small and spade shaped with no pistils its a male, females preflowers are longer and more slender and will eventually grow the pistils. Only 100% way really is to flower a cutting.

Force clones

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I'm currently experimenting with this idea on my current grow. I had a transplant into my tent during the last week of flower for another plant and she showed her sex within the week. I have her now back under a 18/6 light schedule and she is showing slowed growth vertically (also partially due to a super cropping fuck up) and she seems to be stunted for now but only a little.

I understand re-vegging my plant could possibly stress it and cause a hermie but it's a risk I'm taking in the name of experimentation.

No worries though, I have a brand new baby Fem Lemon Kush from Herbies that just popped the soil yesterday whilst under the 18/6.