Castor bean.

At a glance

Care level

Moderate

Plant type

Annual / Tender Perennial

Light

Full sun

Indoor light

direct

Water

Every 3 to 7 days

Mature size

Up to 15 feet tall and 10 feet wide in ideal conditions

Growth rate

fast

Hardiness

USDA 8 to 11

Bloom time

Summer to fall

Care

Provide full sun and well-draining soil. Water regularly, allowing the soil to dry slightly between waterings. Monitor for pests like aphids and whiteflies.

Watering

Water when the top inch of soil feels dry. Avoid waterlogged conditions.

Feeding

Feed with a balanced liquid fertilizer monthly during the growing season.

Pruning

Prune to shape or remove dead foliage as needed, usually done at the end of the growing season.

Repotting

Repot young plants annually, mature plants less frequently when root-bound.

Soil

Well-draining, fertile soil

Soil pH

6.0 - 7.0

Temperature

10 to 28°C

Humidity

40 to 60%

Safety

People

Ingestion of the seeds can cause severe nausea, vomiting, abdominal pain, diarrhea, and in large doses, can be fatal due to ricin poisoning.

Pets

Highly toxic to pets and humans if ingested due to the presence of ricin in the seeds.

Children

The seeds are highly toxic if ingested and pose a significant risk to children. Keep out of reach of children at all times.

Contact allergens

The plant sap can cause skin irritation in sensitive individuals.

Airborne allergens

The pollen may cause respiratory irritation and allergic reactions in susceptible people.

Edibility

The seeds are extremely poisonous and should never be ingested by humans or pets.

How to identify it

• Large, palmately lobed leaves
• Red or green stems
• Spiky, burr-like seed capsules
• Tall, upright growth habit
• Often has reddish-bronze foliage

Height

1.8 to 4.5m

Spread

0.9 to 3m

Leaves

green, red, bronze, deciduous

Flowers

green, red, 0.5 to 1cm

Fruit

red, brown, Late summer to fall

Common problems

• Spider mites — Tiny pests that feed on plant sap, causing stippling and yellowing of leaves, often forming fine webs.
• Whiteflies — Small, white, winged insects that cluster on the undersides of leaves, feeding on sap and weakening the plant.
• Root rot — Fungal disease favored by waterlogged soil, causing wilting, yellowing leaves, and eventual plant death.
• Bacterial leaf spot — Causes small, water-soaked spots on leaves that can enlarge and become surrounded by a yellow halo.

Growing it

Propagation

Seed

When to plant

Spring

Avoid planting near areas where children or pets frequently play due to the extreme toxicity of the seeds.

Grows well with

• Marigold — Marigolds are known to deter some soil nematodes that can affect plant roots, potentially offering a protective benefit.
• Zinnia — Zinnias attract pollinators like butterflies and bees, adding biodiversity to the garden without competing heavily for resources.

Keep away from

• Certain root-knot nematodes — While marigolds can help, some nematodes can still damage the root system of castor bean plants, weakening them.
• Waterlogged soil conditions — The plant is susceptible to root rot in poorly drained soils, which can lead to plant death.

Similar species

• Jatropha — Some Jatropha species share a similar tropical, large-leaved appearance and also contain toxic compounds.
• Oleander — Both plants are highly toxic and often grown as ornamentals, though they belong to different families.

Science

Family

Euphorbiaceae

Genus

Ricinus

Order

Malpighiales

Class

Magnoliopsida

Native range

Northeastern Africa, Middle East, and India.

Conservation

Not of conservation concern.

Castor bean thrives in disturbed soils and can colonize open, sunny areas. It reproduces prolifically through its seeds.

Uses

Ornamental, Source of castor oil (industrial/medicinal use, requires careful processing)

Taxonomy resolved against GBIF.

Questions people ask

Is castor bean plant poisonous?

Yes, the seeds contain ricin, which is highly toxic if ingested.

Can castor bean plants be grown in cold climates?

In cooler climates, it's often grown as an annual, as it cannot survive freezing temperatures.

How fast does castor bean grow?

It's a very fast-growing plant, often reaching its mature size within a single growing season.

Does castor bean attract pests?

While it can be susceptible to pests like spider mites and whiteflies, it doesn't typically attract beneficial wildlife.

Where the name comes from

The genus name, Ricinus, comes from the Latin word for 'tick', referring to the seed's resemblance to a tick. The species name, communis, simply means 'common'.

Good to know

• The castor bean plant is one of the fastest-growing ornamental plants.
• It is believed to have originated in Northeastern Africa and the Middle East.
• The plant's common name, 'castor', likely comes from the Latin word 'castoreum', referring to the beaver's scent gland, as the oil was thought to resemble it.
• Ricinus is Latin for 'tick', referring to the appearance of the seeds which resemble a castor bean tick.