Cytisus scoparius ssp. scoparius

(Broom)

This shrub can live for over 25 years and its seed can stay viable in the soil for decades. No wonder it has infested most of Australia and its range is still expanding. It's still a permitted entry to Australia and a common garden plant, in spite of the fact that it is a serious weed in New South Wales, South Australia, Tasmania, Victoria, and Western Australia, and legislation applies in all states except Northern Territory and Queensland.

Broom is a large shrub, often growing to 4 metres tall. It started life in Australia as an ornamental garden plant with an abundance of uses. For example, the branches were made into brooms, and other parts were used as a substitute for hops, capers, and coffee. It was also used in tanning, as a yellow dye, and in medicine. However, the seeds are poisonous if eaten in large amounts and the foliage can cause digestive problems in horses.

It has attractive leaves, borne mainly as three leaflets around the stem (as shown in the photograph on the left). The shrub will usually lose its leaves in winter and in dry times.

It's a member of the pea family (Fabaceae) so it produces a prolific amount of bright yellow pea-shaped flowers during late spring and summer. Flower colour can vary considerably too because the plant hybridises readily with other species, colour forms and varieties of broom, many of which are also weedy species. The colour can therefore vary from pale yellow - almost white - through to red/purple and various bi-colours (as shown in the photograph below right).

Spread

After flowering it produces pods containing 5 to 8 seeds. The pods 'explode' when fully dry, sending seeds flying about 4 or 5 metres. Germination of the seed is actually encouraged by fire, so the plant has adapted superbly to the Australian environment. The seed can lie dormant in the soil for decades too. The longevity of the seed can often result in a soil seed bank of up to 50,000 seeds per square metre.

The explosive pods are not the only method of spread. Ants move seed, so do vehicles, machinery, footwear, animals, and of course by humans deliberately planting or dumping garden waste.

Unfortunately, the plant is still sold, especially at markets and by some florists, labelled as a non-invasive species. These plants are often actually just different colour forms of C. scoparius.

Control

Do not slash or mow. The best methods of control are to spray, dig out, or cut-and-paint, and this must be done before pods ripen. The bad news is that follow-up hand removal of seedlings will probably be necessary for years.

Information Sources
Blood, K., 2001, Environmental Weeds - A Field Guide for SE Australia, CRC Weed Management Systems, published by CH Jerram Science Publishers.
Weeds of the Blue Mountains website: www.weedsbluemountains.org.au

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