Adam’s Needle (Yucca filamentosa) should bloom mid to late summer. Blooming can be inhibited by your watering practices. Yucca does not like to be over watered always keep yucca towards the dry side. Water regularly in the spring thru fall but sparingly in the winter. It is also important to feed Yucca weekly through the spring and summer.

The fact that your Yucca is producing several rosettes may also be the reason your plant is not blooming.

Try changing your watering practicecs and fertilizing this should make a difference.