I'm not sure where you live , but in the north they're treated as for summer annuals and they die with the first good freezes come the fall, but in warmer climates of course they are considered perennial and may live for a number of years. Perhaps a "temporary" living fence perhaps, is your goal? They are considered tropical!

I believe Newkid lives in WI, therefore, Castorbean can only be grown as an annual that far north..If you're still inclined to grow them, CB should be planted, at the minimum, several feet away from a tree..The roots of CB grow huge, as well as the trunk..I've had CB growing that was so difficult plucking in fall, it was like pulling out a tree..LOL.
BTW, Newkid, this plant is toxic..so if you have pets/children, please keep them away from this plant..toxins includes seeds, leaves, stems, trunk and roots..Toni

I agree with Hopefulauthor. The plant is toxic, it's where ricin comes from. I don't know much about northern plants but I'm sure you could find something better.
Barb