Two houses
Dioecious
Most plants are distinctly male or female
Imperfect flowers
Staminate and pistillate flowers normally sit on separate plants
Wind pollen
Cannabis is wind-pollinated and makes achenes, the dry fruits growers call seeds
Rare combo
A true hermaphrodite carries both sex parts on one flower. That is less common than mixed-sex plants
Monoecious plants
Both flowers
Some plants make male and female flowers on the same body at different spots
Label
Growers often call these hermaphrodites even when the flowers themselves are single-sex
Origins
Mixed-sex plants show up more in some South Asian lines and after stress such as weak light or poor nutrition
Sinsemilla risk
Pollen from those male flowers seeds females the same way a true male does
Garden practice
Cull
Pull mixed-sex plants as soon as they show if you want seedless flower
Keep males
Hold males only when you intend to make seed
Day length
Most strains are short-day plants. Ruderalis and some equatorial lines can auto-flower or act day-neutral
Indoor clock
The grower, not the calendar, decides when sex expression starts
Wild annual cycle
Spring start
Outdoor plants germinate in early spring and grow hard as days lengthen
Late-summer flip
Flower starts when nights get long enough for that variety
Latitude
High-latitude indicas usually need less darkness to flip than low-latitude sativas
Seed drop
Seed sets in fall as weather turns, then the annual dies