Does acidity hurt poinsettias

No, acidity does not harm poinsettias (Euphorbia pulcherrima).

Specifically, poinsettias are acid-loving plants. They prefer to grow in soils whose pH ranges from the acidic to the lower reaches of the neutral zone, from 4.5 to 6.5. In fact, a quite acidic soil pH below 4.8 protects poinsettias from the dreaded black rot (Thielaviopsis basicole) to which they are so susceptible.