Macquarie Valley & Lachlan Valley

Weeds Advisory Committees


Castor Oil Plant

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Botanical Name: Ricinus communis
Other Common Names:


  Not Declared
Landholder Responsibilities: Not declared noxious in this region but is a class 4 in other areas of the State. See DPI website for more information
Why Is It Bad?: Introduced to Australia during early settlement as a plant of cultivation, Castor Oil Plant is now naturalised in all mainland states. It is mostly found in sub-tropical or warm-temperate regions. It commonly occurs along gullies, watercourses and vacant areas such as wastelend and roadsides. Although the seeds can be harvested for the production of Castor Oil, they are also highly toxic. 2-8 seeds are enough to provide a lethal dose for a human. This is not a common occurance however, and livestock will rarely graze the plant due to the offensive smell emmited by crushed leaves. Castor Oil Plant can survive long periods of dry weather as it can retain large amounts of moisture, but it does not tolerate frost at all.


Habit: Shrub
Leaves: Leaves are large, glossy green, shield-shaped, and 15-30cm across. They are divided into 7-9 lanceolate lobes with toothed margins and prominent mid-veins. They have a very unpleasant odour when crushed.
Flowers: Flowers are reddish-green with no petals. Both female and male flowers occur in the same cluster with females at the top and males underneath. Female flowers have 3 bifid styles. Male flowers have numerous stamens with branching filaments. Flowering occurs between December and March.
Fruit: Fruit are reddish-green, softly spiny, ovoid and 1-3cm in diameter. They have 3 segments, each containing 1 seed. These segments explode violently, spreading seeds over several meters. The seeds are smooth, slightly flattened with a fleshy appendage at one end giving it a beetle-like appearance. They are 1.2-1.5cm long.
Roots: Thick and fibrous.

Control Methods

Manual Removal: Single plants may be dug out and debris should be burned to eliminate the danger of toxic seeds.
Chemical Use: Although Castor Oil Plant is tolerant of some herbicides, glyphosate or picloram + 2,4-D give good results. The plant must be actively growing and thoroughly wet by chemical if using foliar spray method. The cut-stump method can also be used for larger plants.
Fire: Plants that have been dug out should be burned.
Slashing & Cutting: Slashing can be effective if combined with shallow cultivation.
Biological Control:
Grazing: Animals will not eat Castor Oil Plant as it is extremely unpalatable, and it is not recommended due to the toxicity levels of seeds.
Cultivation & Scalping: Cultivation can provide some control but for it to be effective it must be repeated and must avoid deep burial of seed.
Monitoring: Successful treatment programs rely on ongoing monitoring of sites. Regrowth and new seedlings can easily become larger infestations if follow-up treatments are not part of the management program


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Image Credit: Michael Burrowes

Image Credit: Michael Burrowes

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