Rhododendron (Rhododendron ponticum)
Why we grow it: Give them moisture and shade, and rhododendron shrubs offer showy red, white, pink, or purple flower clusters in spring and thick, glossy leaves that thrive into the winter.
Deadly parts: The entire plant.
Toxic toll: Who knew both West Virginia and Washington's state flower was a silent killer? Swallow any part of this plant, and you're going to look as bad as you feel. While drooling from the mouth and teary-eyed, you'll begin vomiting violently, just as your pulse slows down and low blood pressure sets in. Death can occur shortly after falling into a coma or during a violent seizure.