No hibiscus is not poisonous to turtles or anything else. In fact the dried flowers are used in herbal teas for people. However, the turtles could be toxic to the hibiscus plants in that they can do...
Yes they are very poisonous. Every part of the plant is poisonous, especially the sap. Be careful when handling this plant, it can cause eczema, and other skin rashes. Definitely do not allow...