This is a naturally occuring hybrid of Yucca Thomson and Yucca Rostrata, only found in the Big Bend area. This Yucca tree is winter-hardy around -15 (Zone 5) and prefer well-draining soil. They have beautiful blue rigid leaves with yellow highlights along the edges and put off large white blooms in the summer. Some grow as a single head but many are multi-headed. You can leave the plant as-is for  a natural look or many homeowners prefer to trim the browned/fallen leaves which give it  a neater trimmed look.