The words deadliest plant is castor bean plant it has a poison called ricin. The seed of the castor bean plant is very deadly. The castor bean plant makes its food by using air water and soil. There are other deadly plants like snakeroot and monkshood also called wolfsbane. Monkshood is purple and has flowers but is very deadly. snakeroot will poison cows and the milk of the cow gets poisoned and if someone drinks the milk of the poisoned cow they can die. they use hydrogen from water nitrogen from soil and oxygen from air to make poison