Castor Bean Germination Techniques

Seeds

• Castor beans, the plant's seeds, are oval, rounded or egg-shaped and about 1/2 to 1 inch long. Colors vary depending on the cultivar, but the overall color is usually light brown, with markings of darker brown, gray, yellow-brown, black, maroon and white. Seeds form in spiky capsules in the top branches, and there are three seeds per capsule. They usually sprout within 10 to 21 days after planting, but can be slow to germinate or have irregular germination. Various practices help improve the speed and percentage of germination.

Scarification

• Castor bean seeds have hard seed coats that prevent water from penetrating inside. Improve germination by rubbing the seeds with sandpaper or nicking them with a file -- a process called scarification. The scratches or small holes allow water to enter the seed. Soaking seeds also hastens germination, either alone or in combination with scarification. Soaking for 12 to 24 hours in water also improves germination rates. A study by Rajesh Kumar and Amit Srivastava published in "Advances in Bioresearch" reported that castor bean seeds presoaked for 24 hours before planting had the highest germination rate -- 86.5 percent -- when compared to seeds soaked for 12 or 36 hours.

Caruncle Removal

• Some seeds have specialized structures called elaiosomes attached to them. These have rich stores of proteins and lipids, and are meant to attract ants and other seed-eating animals that aid in seed dispersal. Castor bean seeds have such a structure, called a caruncle, at the base of the seed. Remove the caruncle to improve germination, and soak the seeds in water as well.

Planting Depth

• Kumar and Srivastava also studied the effect of planting depth on the germination of castor bean seeds. They found that maximum seed germination of 92.5 percent occurred at a sowing depth of 2 inches, followed by 84 percent germination at a depth of 3/4 inch. Seeds sown even more shallowly at 4/10 inch had the lowest rate of 76.5 percent. The most deeply planted seeds, sown at 4 inches, did not germinate at all.

Precautions

• All parts of the castor bean plant are poisonous, with the highly toxic compound ricin concentrated in the seed coat. The seeds are toxic and can be fatal to humans and other animals. The seed coat needs to be broken to release the toxins. Use care when handling the seeds. Inhaling seed dust can cause allergic reactions. In addition to the plant's use as an ornamental, castor beans contain 33 to 55 percent castor oil, which is not toxic. The oil is used as a dietary supplement and also in varnish, paint and lubricants. Don't grow seed-producing castor bean plants where children can access them. One option is to remove the female flowers on garden plants so seeds never form.