Answer: Actually, the color change in nandina is related to temperature. In fall most will turn purpley/bronze and then more red/crimson in winter, especially if they are in sun and there is some frost. They'll grow in any fairly good soil. They do not like to have dry feet, however, so keep
the soil well mulched and water when nature doesn't provide it during the growing season. Temperatures have been warm this fall--that might explain why yours haven't turned red.
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