Answer: Castor bean seeds need plenty of heat to germinate, and the seedlings grow very quickly and need good bright light to thrive. You could start them in individual pots, at least three inches across, just a few weeks before you would plan to set them in the garden. In the interim, you would need to keep them under lights or in an extremely well lit location because they are strong sun lovers; they would also need to be hardened off prior to planting.
To prepare the seeds, nick or make a little chip in the hard seed coat with a razor blade or sharp craft knife, then soak in tepid water for several hours or overnight until the seed softens.
Then plant about a half inch deep in dampened sterile soilless planting mix or dampened seed starter mix. Cover with clear plastic wrap (to maintain humidity) and set in a warm bright location but out of direct sun. Some gentle bottom heat such as from a horticultural heating mat or cable would also be helpful, or keep it in the warmest room available until germination occurs. At that time, move them to the brightest location you have.
Alternatively, once the soil has warmed and about a week after all danger of frost has past you could plant them outside where you want them to grow. Nick and soak the seeds before planting and keep the soil evenly moist until they begin to grow. The plants grow very fast once the weather is warm.
Good luck with your castor beans!
I should mention that the seeds are poisonous, so do not allow children or pets access to them.
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