Will 12/12 work for sexing on 3-4 wk. old plant?

How old does a plant have to be before you can change to a 12/12 photoperiod to determine the sex? I only have room for 2 plants in my growing area. I'd like to find out if at least one of these is a female, take a couple of clones from it, and then devote the space I have to growing these 2 clones through a proper growing cycle.

The 2 on the left are 22 days old since germination (6 inches tall), the 2 on the right are 17 days old (4 inches tall).

Does anyone know if you can successfully determine the sex of plants this young by switching to a 12/12 day/night cycle?

Thanks

yeah you can flower them that young. and they will show sex in 1-2 weeks after 12/12. id recommend flowering around week 5 with cfls/floros. depending on growthrate maybe earlier or later. id give those a bit longer if i were you. flowering that small could take away from your yield. you will need some mroe lighting too. id add a few cfls or maybe get hps for flower if you can. if you get hps veg them longer

Erysichthon said:

yeah you can flower them that young. and they will show sex in 1-2 weeks after 12/12. id recommend flowering around week 5 with cfls/floros. depending on growthrate maybe earlier or later. id give those a bit longer if i were you. flowering that small could take away from your yield. you will need some mroe lighting too. id add a few cfls or maybe get hps for flower if you can. if you get hps veg them longer

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Thanks for the advice. You're right, I definitely need to get some more/better lighting, but I wanted to make sure I had a least one female before I went out to buy more "supplies".

When you say "flowering that small could take away from your yield", you mean the yield of the plants in the pictures, right? Cause I'm not really planning on doing anything with these plants, except for getting some clones from what I know is a female, and then growing 2 of those clones to fruition.