Answer: In my experience early spring is the best time to divide them, but it can be done almost any time if you are careful to keep them well watered. The least desirable time to do it would be while they are in bloom because you would have to remove the blooming stems to compensate for root loss during the dividing process. These plants prefer full sun all day long, but yes, they are quite capable of tolerating a half day of hot afternoon sun. They will also grow in a half day of morning sun.
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