Answer: Overwintering perennials in pots can be tricky. Some gardeners will cover the pots with row cover fabric and/or place them in a cold frame. Another method and my personal preference is to sink the pots into the ground in order to insulate the plants' roots. Another method would be to mulch around them or otherwise insulate them. Keep them in a sheltered spot in the shade if possible. (The reason for shade is to keep them from freezing and thawing during temperature swings.)
Watering is a judgement call. You will water less as the temperatures cool down, but the plants should never go bone dry. On the other hand, if they are too wet they may rot although this is not usually a problem if the pots are kept outdoors where air circulates freely. Finally, I am assuming these are in nursery type pots -- you should be aware that terra cotta pots generally self destruct if allowed to freeze. Good luck with your project!
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