In its natural environment a photoperiod cannabis plant will grow for around 8-9 months. They will start growing in early spring, and be harvested in late autumn. Indoors, photoperiod cannabis plants can be kept in veg for years. But most growers will give around 6 weeks of veg, and then flower the plants. The length of the flowering period will depend on whether the plant is Indica or sativa dominant. Autos will grow for around 90 days before they are ready for harvest. But again their flowering period will depend on how Indica or sativa dominant the plant is.