Agapanthus (not a true lily, btw, but a fleshy rooted perennial) has a range of hardiness depending on species. If the tag says 10F, then I'd venture this is one of the less hardy forms, as that's quite a bit warmer than any zone 5 :-)

I find these are very successfully grown as a container plant. First, they appreciate being rootbound and tend to bloom more frequently in my climate under these conditions. Second, container culture offers the option for very good drainage, as they tend to rot out in our wet winters. And in climates like yours, they can be moved inside for winter protection.

You might want to try posting a similar inquiry on the Perennials forum. I know the topic of growing agapanthus in colder climates has come up before. And it would help if you could provide the full botanical name and cultivar to narrow down the hardiness issue.

thanks a lot!