HESPERALOE PARVIFLORA 'THUNDER WOLF'
Red Yucca aka Hesperaloe parviflora is a cold hardy yuccacea from Texas and Mexico. This unique form of Red Yucca we call 'Thunder Wolf' in honor of the mascot at the local college that grows these in great numbers (Colorado State University Pueblo). These plants are gown out in open plains where the wind whips thru them all winter long. Plants have taken -22F and survived with no damage. However from experience we suggest protecting the Hesperaloe the first year so they get enough roots to bulk up for the next winter.
I do not guarantee these in a zone 5/6 because everyones growing conditions are different but this would be a good trial plant to grow in your cold outdoor garden. Try to plant outdoor 90 days before 1st hard freeze.