Good Morning Fabiene, 

Thank you for contacting the U of M Extension Service. 

Please click on the following link about castor beans: https://hort.extension.wisc.edu/articles/castor-bean-ricinus-communis/

This information states: 

The seeds are extremely poisonous, so keep plants out of reach of children (or trim off flowering spike if this is a concern).

The plants are not poisonous, only the seeds. You can compost the plants and I would suggest you pull off the seeds and dispose of them in the trash. 

Good Luck!