I've found this incredible book that gets into details not normally found in a gardening book. The book is Cannabis Encyclopedia by Jorge Cervantes. The king pothead! After reading his book one can be sure that Cannabis doesn't permanently ruin your intellect!
Cannabis plants are dioecious, male plants and female plants and hermaphrodite misfits with both sexes on one plant. One of the hurdles one must face with this plant is not knowing whether a seedling is male or female and one puts a lot of time raising these seedlings only to find they are all or a large part males. Unless one is growing for seed all one wishes for are females. The boys get killed.
Then there are the hermaphrodites, an unknown. It is almost common to one day find just ONE male flower on one of their female plants in the midst of female plants, the fan is blowing all of the time. Blowing that fine fine pollen only later to find that one flower has fathered seed in all of the plants! The process of making seed is a huge energy expenditure and reduces the amount of 'bud' or female flower or 'cash crop'.
In a nut shell, one can increase the likelihood of one sex or another during the first 2 weeks of life as a growing seedling. To promote your seedlings to be female; increase Nitrogen (for males increase potassium), higher humidity and moisture in the air and soil for females (males lower humidity and dryer soil), fewer daylight hours 14 versus 16/18 hours (for males the reverse) and using blue light in the vegetative state. Red light during the seedling stage promotes males. Red spectrum light is always used to shift the female plants into reproductive growth at the same time changing the day/night hours 12/12.
The moral of the story is the sex of a dioecious plant is not carved in stone within the seed. The environment is in a very large way responsible for determining the sex.
Those who try to grow this plant on a budget and don't purchase both sets of bulbs (blue spectrum and red spectrum) will most likely have chosen red spectrum. As the studies show, red spectrum light used on seedlings will promote males. Bummer. Go get those blue bulbs to have both spectrums!
In addition, those that have purchased expensive seed ($10 to $20 per seed or more) can relax knowing the sex of their plants can be manually enhanced. Otherwise, cloning was the only option to be sure of females. Hermaphrodites can still pop up anytime with females.
The power of the Cannabis plant for reducing pain, nausea, boosting immune systems, the few studies out there about cancer cures with the CBD's (not the THC) are pretty convincing. Humans have evolved with this plant to the extent we have receptors DESIGNED just for CBD (canabinoids). Our body actually makes its own, checkout endocanabinoids. Don't know and don't care about the laws and politics surrounding this plant, the beauty of this book is it deals with just ONE PLANT, an oversize book an inch thick and I think is a must have for any gardener's library.