Can Castor Bean Seeds Survive Freezing?

Mild Winters

• Castor beans grow as a perennial plant in climates that experience winters and springs without the threat of freezing, snow and frost, such as U.S. Department of Agriculture plant hardiness zones 9 through 11. In all other climate zones, the castor oil plant grows as an annual. Castor beans are typically planted in the month of May, once all threats of frost have passed. (See References 1 and 3)

  Castor beans require warm soil and a warm growing season throughout the spring and summer months. At planting time, the soil needs to be at least 70 degrees Fahrenheit. Temperatures in the 70s and 80s are ideal for growing; however, the castor bean plant is capable of surviving minimum temperatures of 40 degrees Fahrenheit in the daytime and 36 degrees at night. (See Reference 3)

Growing Conditions

• The castor oil plant is not able to survive frost or temperatures that dip below freezing. Freezing temperatures kill the plant and impede germination of seeds. (See Reference 4) Castor beans have a growing season of 140 to 180 days, all of which need to be frost-free in order to successfully grow the plant. If you live in a climate that experiences early or late frosts, it is best to start castor beans indoors. Transplant your seedlings outdoors once the threat of frost has passed. Castor beans require full sun and moist, fertile, well-draining soil. A regular schedule of watering and fertilization is also required to keep your plant healthy. (See References 1 and 3)

Reproduction and Germination

• Castor beans reproduce via seeds following flowering. They reach maturity and reproduce within the first growing season. Freezing temperatures stop the castor oil plant from reproducing in colder climates, which is why it grows as an annual in such climates and needs to be re-planted each year. Freezing temperatures also put a stop to germination. No matter which stage of germination your plant is going through, exposure to frost or freezing will impede your seeds from properly germinating. Even a period of exposure as little as 24 hours is enough to halt the reproductive cycle of the castor bean plant. (See Reference 4)

A Word of Caution

• When discussing the frost tolerance of the castor oil plant, it is very important to note that all parts of the plant--including the stems, leaves and seeds--are poisonous. Only the oil, which is extracted from the seeds, is benign. Do not handle a castor oil plant without gloves, due to the risk of skin irritation. Castor bean plants are especially dangerous to have in yards and landscapes where pets or small children are present. Ingesting any parts of the plant causes an array of symptoms, from digestive upset to death, depending on the amount consumed. (See References 1 and 3) Castor beans are also considered an invasive plant in the state of California, as they interfere with the natural vegetative landscape. (See Reference 4)