The most common method is to force flower a labeled clone to determine the sex, rather than the incorrect method of forcing the seedling and then reverting it to vegetative growth again.
If you are a seedling grower who does not clone, or a grower who has no seperate vegetative and flowering grow spaces, the easiest method is simply to wait for the preflowers (primordia), and sexual maturity to appear while the seedling is still in vegetative growth.
Seedling growers who don't clone are really missing out on the full potency potential of their finished crop whenever they force their seedlings before they've become sexually mature.
Preflowers, as opposed to full blown flowers, generally appear after the fourth week of
vegetative growth from seed. Check carefully above the fourth node. Please note that preflowers are very small and impossible to differentiate without magnification. A photographer's 10x loupe is handy indeed when examining preflowers.
As the images below demonstrate, the female preflower is pear shaped and produces a pair of pistils. Frequently, the female preflowers do not show pistils until well after the preflowers have emerged. Thus, don't yank a plant because it has no pistils.Pistillate preflowers are located at the node between the stipule and emerging branch.
Female (pistillate)
Female (pistillate)
Image courtesy of Uncle Ben
The male preflower and flower may be described as a "ball on a stick." Frequently, a male plant will develop mature staminate flowers after prolonged periods of vegetative growth. These appear in clusters around the nodes.
The following image shows a male plant in early flowering. Staminate flowers are located at the node between
the stipule and emerging branch. Note the clusters of flowers.
Male (staminate)
The image below shows a male pre flower after 24 days of 18/6.
