Mail in labs can now tell you a seedling's sex from a punched leaf sample at about ten days old, weeks before pre flowers show. At a few dollars per plant it makes regular indica seeds far more practical in a small space, since the males go before they use any real room. How the sampling works, turnaround times and which labs members have used are reviewed on https://kushindicaseeds.com (https://kushindicaseeds.com), along with the occasional wrong result. It is not worth it for feminized packs, obviously.