As cannabis is a annual plant - i.e. reaches maturity within one season - for a plantation to be operational continuously, a grower has to take care of constant supply of seedlings. Two schools of growing say that this should be done either using freshly germinated seeds, or clones, cut from the mother plant.
Either way, you will have to get baby plants in order to bring the up to maturity, when they will produce heavy buds of marijuana. Those seedlings require special care, slightly differing from the conditions that are nurturing older plants. Humidity should oscillate around 80%, slightly less intensive light and possibly a 24 hour lighting cycle.
In order to facilitate the process of propagation, a variety of handy accessories is available, such as germination trays, heated propagators etc. For large scale productions, a dedicated box for clones and seedlings might be a good idea that allows one to use the available space at its maximum, increasing total yield.