Black edges on bracks
by Vicki
(Yellville AR)
poinsettia
Doug says that the black or brown crispy edges on the leaves is due to a change in humidity and watering from the greenhouse to the home environment. Your house is much drier than the greenhouse and this is what has happened. Nothing you can do to reverse this process on existing leaves.
Do not overwater the plant - this is another partial cause of tip and leaf browning.