Certified GKH Gardening Expert
You don't encourage yucca to bloom. They only bloom when they're ready to. If the yucca is planted in the ground, it's more likely to bloom than container-grown plants kept indoors. However, it will still be awhile before it is mature enough to produce blooms. In fact, with some yuccas, it can take years before you see any blooms. My advice...be patient.