Question:
How often should I water my poinsettia?Answer:
The key to watering a poinsettia is the moisture content of the potting soil. Check the potting soil daily with your finger. When the soil surface becomes dry to the touch, water the plant until water begins to flow out the bottom of the pot. Discard the excess water. The pots of most poinsettias are set inside decorative pot covers. When watering these plants, carefully remove the poinsettia from the pot covering, water the plant in the sink, then drop the poinsettia back into its pot cover. 
Both over- and under-watering cause problems for poinsettias. Over-watering will cause the lower leaves to turn yellow and drop. Over-watered plants may also develop root rots and die. Dry plants wilt and also drop leaves prematurely.
Learn more in this article: Guide to Selection and Care of Poinsettias