Garden geranium is a native of South Africa that has become a weed in other countries with a Mediterranean climate similar to much of southern Australia. It can grow in variable conditions including drought prone areas due to its underground rhizome tubers, and can dominate understorey vegetation. Garden geranium is an escaped garden plant that now threatens the natural environment and could potentially threaten agriculture.
Garden geranium, a member of the South African geranium family, was originally planted in gardens for its ornamental value in southwestern Western Australia. Its distrubtion is localised in southwestern Western Australia. It has since become a naturalised weed in peppermint woodland (Agonis flexuosa) 2 km inland from Hamelin Bay in the Margaret River region. Its introduction to Australia is estimated to have occurred in the early 20th century, when a timber settlement was in place.
Garden geranium reproduces bothvegetatively and via seeds. Seedproduction is prolific, but plants canalso be propagated from stem cuttings,fleshy roots or tuberous (rhizome) roots.The underground rhizome system, upto 6 m in length, ensures its survival in dry periods and at times when seed production is not successful. Soil distrubance is thought to have been the major cause of its more recent population increase, as the rate of spread was slowuntil roadworks using graders and trucks occurred. Seeds and broken pieces of the rhizome are able to propagate easily indisturbed soil. It is possible for seeds to remain viable in the soil for a long period of time, as some species of Pelargonium have in-built chemical inhibitors to prevent all the seeds germinating at the same time.
Garden geranium is a low, sprawling plant, growing from a central rosette ofleaves and forming flowering branches that spread out and continually produce flowers from the tip of the branch. It grows to approximately 200 mm highand forms an underground tuber up to 6 m in length. The stems are herbaceous and slender and can appear straggly. Longhairs cover the entire plant.
The leaves are 20–70 mm in diameter, have irregular edges, are mostly round in shape and are lobed in up to five separate segments. The plant can also be distinguished by purple-brown horseshoe-shaped markings on the leaves.
The flowers are white or grey in colour, with up to five petals in an arrangement similar to an umbrella. Fifteen flowers are possible on each plant.
Seeds are contained within a distinctive pod shaped like a crane’s bill. A single plant will die out after a few years, but will easily re-establish new individuals because it is a prolific seed producer.
The weed is exceptionally adaptable, will tolerate arid conditions, and can also thrive in areas of high rainfall.
CRC for Australian Weed Management: Greg Keighery (CALM WA), Annaleisha Sullivan (GeoCatch WA), Rod Randall (WA Agriculture / Weeds CRC), Robin Parer (Geraniaceae Nursery).
Because there is only the one known infestation of garden geranium, it can potentially be eradicated. New outbreaks should be reported immediately to your local council weed officer. Do not try to control garden geranium without their expert assistance. Control effort that is poorly performed or not followed up can actually help spread the weed and worsen the problem.
Garden geranium (Pelargonium alchemilloides) is not declared in NSW under the Noxious Weeds Act 1993.