I can't imagine a lotus surviving outdoors in a zone5, but I'm always ready to be surprised. I would overwinter them in a tank or tub with depth of water anywhere between 16 and 50cm and at a temperature between 8 and 13C from October to March.

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Zone 5 is about the edge of lotus's hardiness. If the plants are small, they may not make it through the winter. I would go with Peter's advice. Just keep them in water, maybe in a cold garage or basement where they can stay dormant but away from really cold temps.

update! I have them in the greenhouse, I thought they would continue growing, but it seems they are going dormant. The leaves are coming off, but I checked one out and it has made a little tuber. I did put one in the pond just to see how it does. My pond is 48" deep, way below the frost line here.Most of the websites say lotus are hardy to zone 3.

From my understanding, you should be okay. It is fun to experiment though, because then you really know which method is the most successful.