How to Grow Castor Bean Plants

castor bean plant

The Spruce / Evgeniya Vlasova

Some plants, while they have roles to play in your landscaping, are hardly conversation pieces. For example, catmint can be an excellent ground cover, but rarely will a visitor walk onto someone's landscape and remark, "Wow, look at that catmint!" It is not designed to evoke such a response—instead, its purpose is to play a supporting role. Castor bean plants, on the other hand, have star power.

What gives castor bean plants their star power? Native to Africa and the Middle East, castor bean plants grow quickly, adding between 6 and 10 feet per growing season and featuring star-shaped leaves with vibrant red seeds. It can be planted straight into the garden in late spring or started from seed indoors about six to eight weeks before the last frost of the season.

Botanical Name  Ricinus communis
Common Name  Castor bean
Plant Type  Herbaceous perennial
Mature Size  6–10 ft. tall, 2–4 ft. wide
Sun Exposure  Full sun
Soil Type  Moist but well-drained, rich
Soil pH  Neutral to acidic
Bloom Time  Summer, fall
Flower Color  Greenish-yellow
Hardiness Zones  9–11 (USDA)
Native Area  Africa, Middle East
Toxicity  Toxic to humans and animals
castor bean plant

The Spruce / Evgeniya Vlasova

closeup of castor beans

The Spruce / Evgeniya Vlasova

castor bean plant foliage

The Spruce / Evgeniya Vlasova

Castor Bean Plant Care

Castor bean plants are typically grown during the summer in most environments and will quickly reach sprawling heights, making them an eye-catcher in your landscape or a great option for a living privacy fence if grown together. However, height is just one attribute that makes castor bean plants stand out in your landscape. Their coarsely textured leaves create dramatic textural contrasts when placed alongside plants that have smaller leaves.

While the flowers on the castor bean plant are insignificant, the red seed capsules covered in spines do possess ornamental value. When these pods dry, they explode, turning the seeds that had been trapped within into projectiles. Even the seeds themselves are attractive, sporting an endless number of colors and patterns. It is perhaps the appearance of these seeds that give the plant its genus name, Ricinus, which translates to "tick" in Latin.

Many people are familiar with the fact that castor oil, an old-time laxative and purgative, is pressed from castor bean seeds. Additionally, some gardeners use castor beans in companion planting to serve as mole repellents. That being said, castor beans are not true beans—that's just a nickname. The plants belong to the Euphorbiaceae family, which makes them relatives of poinsettia plants and wood spurge. Since castor beans are tall, slim plants with large leaves that act like sails in the wind, be sure to stake them unless you've located them in a spot sheltered from high winds. Generally, the plants have no serious issues with pests or diseases.

Light

Castor bean plants like full light and should be planted somewhere in your landscape where they get at least eight hours of sunlight a day. Avoid putting the plant below any towering trees, which can impact the amount of light it can get. Additionally, keep in mind that the more sunlight your plant gets, the fuller and more productive it will be.

Soil

Soil that is rich and moist will produce the best results for your castor bean plant. The mixture should be nutrient-dense and hold moisture well, but should not be boggy or easily waterlogged. If your intended planting zone isn't known for its soil, you can amend the mixture with some organic matter to increase the nutrient density.

Water

Castor bean plants like soil that is consistently moist, but you should take care not to overwater them. Generally, the plant likes around 1 inch of water per week, either from rainfall or manual watering. Keep in mind, that amount may need to increase if you experience drought-like conditions or are having an especially hot summer.

Temperature and Humidity

True to their tropical nature, castor bean plants like warm temperatures and above-average humidity levels. If planted in the right USDA hardiness zones, your plant should be more than happy. As a rule of thumb, castor bean plants need soil temperatures of 50 degrees Fahrenheit to 64 degrees Fahrenheit to be planted outside and will grow and thrive best in an environment that ranges from 68 degrees to 80 degrees Fahrenheit consistently.

Fertilizer

For best success, feed your castor bean plant once a month with a general, all-purpose fertilizer.