Male plants produce pollen. Female produce flowers. If the female becomes pollinated her flowers will produce seeds. If she is un-pollinated her flowers will grow bigger, producing coveted resin laden buds with cannabinoids such as THC – the primary chemical in cannabis that gets you high.
When a female is pollinated the buds do not grow as large or potent. This is why male plants are typically unwanted in a garden when the goal is to produce resinous buds. Male plants produce some resin but not nearly as much as the female plants.
Physical characteristics of male and female plants
Male plants tend to grow a bit taller than females and they have pollen sacs that look somewhat like clusters of mini ripe bananas. The pollen sacs have a small stem with a football shaped ball at the end. You can spot them at the base of the branches where they connect to the stem. Females have pistols with white or amber hairs. Look for slender pistols at the base of branches with two white or amber hairs growing out. The male sacs release pollen that is caught by the female pistols, pollinating the female. A small percentage of cannabis plants are hermaphrodites and have both pollen sacs and pistols.
Identifying male vs. female plants
Male pollen sacs and female pistols usually start to show up in late vegetative growth. Once the plant switches to flowering the pollen sacs and pistols will show up aggressively. This is when they can become a problem if you are trying to avoid pollination. If you want to learn earlier the sex of the plant you just have to force a change of the light schedule. Cannabis experiences a phenomenon called photoperiodism which is a response to changes in day length. When the days become shorter, or when the plant is kept in darkness indoors for 12 hours per day, it switches to a reproductive mode where it slows its vegetative growth function and switches energies to the production of sex organs instead. By shrouding the plant in darkness for 12 hours a day it will quickly switch to its reproductive mode and you will be able to spot the telltale pistols and pollen sacs.