Answer: It's not normal for nandina to develop black leaf tips, but it might be due to environmental or transplant stress and it may never happen again. I'd prune away the damaged foliage. Cut the stems of the affected foliage down to a level that they are hidden by the rest of the foliage. The stem will sprout again and the new foliage it develops should be healthy.
Best wishes with your new plants.
Q&A Library Searching Tips