To plant castor beans, soak the beans in a cup of water for 24 hours. Drain the cups, and sort the beans to find those with a pink or white sprout growing at one end. Discard the unsprouted beans, and plant the sprouted beans in a container with high-quality, well-draining soil. Keep the soil moist and maintain soil temperatures of 70 to 75 F to encourage growth. Transplant the beans outdoors after the danger of frost has passed.
When sowing seeds indoors, allow 15 to 20 days for germination, and start the seeds six to eight weeks before the last expected frost of the season. To promote successful germination, rub the seeds lightly with a coarse file before placing them in the water to soak.
When planting castor beans directly in the garden, wait until May, or when soil temperatures have warmed significantly, to plant the beans. Work the soil to ensure it is loose and well-draining, and place five to 10 beans in each hole along the row.
Allow the plants to grow to a height of 3 to 4 inches before thinning to one plant every 12 inches. As castor is toxic, do not allow children or pets to consume any part of the plant. To prevent castor from becoming invasive, deadhead the flowers and dispose of them.