I accidentally overwintered a small (10 in) Red Star Cordyline in a plunge pot outside. I have read they are hardy to zone 7. There was only about 3 inches of straw over it, the leaves died off but has come back and is now about 14 inches tall. Has anyone successfully overwintered a more mature plant - say, 2 to 3 feet tall? If so, did the leaves survive? How was it protected?