Castor plants are gorgeous, and can grow to be huge! Mine tend to be in the 4-6 foot height range, but I've seen them get even taller!
These are warmth-loving plants. I've had no trouble growing them in zone 7 and they could probably be grown farther north without much difficulty. However, it's important whether you're transplanting seedlings or direct sowing seeds in the ground to wait until the ground is warm and there is no risk at all of frost.
CAUTION: The seeds of the castor plant are HIGHLY TOXIC. DO NOT CONSUME ANY PORTION OF THEM. DO NOT LEAVE THEM WHERE CHILDREN OR PETS CAN GET AT THEM.
A lesser caution: The seed pods, shown in last image, are kinda spiky. I strongly advise using thick gloves if you"re going to be handling them.