The castor bean plant (Ricinus communes) walks a fine line between landscape-acceptable ornamental and highly toxic weed. It grows fast, reaching 6 to 10 feet tall in a few months. In U.S. Department of Agriculture plant hardiness zones 9 through 11, it grows as a perennial, but with the fast growth rate it works well as an annual in frost-prone areas. This plant is only suitable for areas where children and pets never go because the whole plant is poisonous and its bright red seeds especially so.
Spacing and Landscape Suitability
The castor bean plant needs full sun and loamy soil with fast drainage. To create a dense planting without causing crowding, leave at least 4 feet between plants. Because of the highly toxic nature of the seeds, leaves and stalks, never grow this ornamental in areas where children and pets have access to the garden. The seeds are the most poisonous part of the plant. They fall naturally in the fall, creating a potentially toxic hazard at ground level.
Watering and Drought Tolerance
To support their rapid growth, castor bean plants need abundant water early in the spring and summer. Water once a week, giving each plant a total of 1 inch of water at each watering session. Apply it slowly with a hose or soaker hose so water can seep down around the roots. Adding a lot of water all at once will cause it to run off and away from the roots. After castor bean plants reach their mature height, a brief period of drought won't damage or slow growth.
Fertilizer for Sustained Growth
Regular fertilizer through the growing season keeps a castor bean plant growing strong and lush. Once a month, apply a general purpose fertilizer such as a 10-20-10, 5-10-5 or a 10-10-10 formula. Use 1/2 cups for a 100-square-foot area around the plants. Once you finish fertilizing, water the soil with 1 inch of water. (This should replace one the the regular weekly waterings.)
Wind Damage and Staking
Ideally, grow ornamental castor bean plants in a protected area as strong winds can break the stalks and shred the leaves, making the foliage look ragged. In windy spots, keep the plants from falling over with stakes. Drive a stake 10 to 12 feet tall (or as tall as the height of the plant) into the soil 12 inches from the base, and loosely tie the stem to the stake.
Preventing Spread and Toxic Poisoning
Keep castor bean plants from taking over the garden by clipping the flower heads before they produce seeds, but you have to get every single one. This also helps keep the toxic seeds off the ground. Clip flower stalks where they attach to the stem, and wash the shears with soap and water. In cold areas, the will die with the first frost. Remove dead plants and discard them in the garbage. All parts are poisonous, so don't put them in the compost.
- The Wisconsin Master Gardener Program: Castor Bean, Ricinus Communis
- Fine Gardening: Genus: Castor Bean
- Missouri Botanical Garden: Ricinus Communis
- Backmans: Fertilizing Annuals and Perennials
- University of Illinois Extension: Watering Correctly Saves Time, Money, and Plants
- University of Vermont Extension: Fertilizing Landscape Plants