In most parts of the world the climate is such that cannabis is an annual plant, living roughly 6 months. If pollinated it would drop seed and then die, fertilizing the earth for the next generation. Indoors, mothers can be kept for several cycles but obviously you'd be cutting it back regularly so it wouldn't have the chance to grow to any great size. Once the trichs on your plant begin changing from clear to cloudy it's just a matter of harvesting at the ratio you prefer. Waiting to harvest=waiting to cure=waiting to smoke =)