Phormium Tenax Seedlings help please

Hi. I wanted just a couple of hardy Phormium Tenax for our garden (needs to be tough up north) and so I grew some from some seed i collected..... so here i am a year and a half later with not a couple, but 27 seedlings/plants which i have just potted on to bigger pots.... but.... i cant find any advice on how hardy they are when young, would these be ok outside in their pots during their first winter? (they are about 2-6 inches high so far), we are really wet and cold in winter so wondering if i should keep them in the conservatory until next year and then put the pots out/plant out in spring (and also it would mean any i give away wont die as well).