How to Germinate Castor Bean Seeds

Castor bean plant

Castor bean is a fast growing tropical plant, and it's one of my favorite annuals.

I love my red castor beans, they add a wonderful contrast of color and texture to my tropical garden.

I get tons of compliments on them, and everyone asks what they are.

Every fall I collect the seeds and sow them in the spring. 

Last fall, I showed you how to collect castor bean seeds. Well, now is the time to sow them, and in this post, I will show you how. 

Castor bean seeds can be directly sown in the garden; but in areas with short growing seasons, it's best to start them indoors 4-6 weeks before last frost. Castor bean seeds are not a good candidate for winter sowing, they will only rot.

Castor bean in tropical garden (front right)

Castor bean plants can be challenging to grow from seed. The key to successfully germinating the seeds is to soak them in warm water before sowing. I soak them for about 24 hours.

Soak castor bean seeds before sowing

After soaking the seeds, it'll look like one end has popped out. Drain the water and sow the seeds like you would any other seed.

Castor bean seeds after soaking

It's a good idea to sow them in a deep container, unless you plan to transplant them right away.

It only takes a few days for the seedlings to outgrow seed starting cells and trays. 

The rule of thumb for planting seeds is to plant twice as deep as the seed is wide; castor bean seeds should be planted 1" to 1 1/2" deep.

I like to make a hole then drop the seeds in rather than pushing the seed into the soil. Cover the seeds with soil, but don't pack the soil tightly over them.

Cover the container so the soil won't dry out. Keep the soil evenly moist, but don't allow it to get soggy. Soggy soil may cause the seeds to rot.

Castor bean seeds take a long time to germinate, so be patient. I've read online that the germination rate for castor bean seeds is 10-21 days. I've had seeds take as long as a month before finally sprouting.

Castor bean seeds sprouting

Once the seeds sprout, the seedlings grow very fast and can get leggy in only a few days. I start to harden off castor bean seedlings as soon as I see sprouts. If it's too cold to put the seedlings outside during the day, add some grow lights above the seedlings.

Castor bean seedlings

Protect castor bean seedlings from frost and plant them in the garden after all chance of frost is gone. Castor bean plants need a full sun location to grow their best. They will tolerate shade, but the plant will stay small. Plant in fast draining soil in a location where they will be protected from high winds. They like lots of water but don't like soggy feet. You could grow them in a large pot, but their growth will be stunted.

Castor bean leaf

Castor bean plants and seeds are poisonous if ingested. If you're concerned about the toxicity of the seeds, you can cut off the flowers to prevent seed formation. (But consider saving a few to grow for next year.)

Read my tips for starting seeds indoors post for more details and general tips of starting seeds indoors.