Hardy lilies can be planted in containers but won’t survive winter in them. This is true for all hardy perennials, shrubs and trees. In containers, they will repeatedly freeze and thaw and freeze and thaw all winter long and this kills them. In the ground, they go dormant and stay frozen…which is what they need. If you want hardy plants in containers, you’ll have to sink those containers into the ground up to the top of the pot for the winter.