What is a weed?
We often think of weeds as those small annoying perennial plants like thistles and sour-sobs that grow during the wetter months. However, any plant that is growing at a site where it is not wanted can generally be regarded as a weed. This can include bushes, trees and even native species when they grow outside of their natural range. Weeds often smother and out-compete locally indigenous plants, degrade and destroy unique habitats, and threaten the wildlife dependant on that habitat.
When does a garden plant become a weed?
Australia today is a multicultural country but it is not only people who have made their home here from around the world. Our gardens are full of plants that originated from across the globe. Some are grown for food or economic gain while others are grown for their flowers or because they remind us of our cultural heritage.
Many common garden plants have escaped into open spaces and native bushland where they threaten the health and value of those areas. Apart from the environmental damage these escapees pose, the substantial expense of removal and control are another cost of weeds. Some garden escapees are already well established in natural areas while others are in the early stages of invasion. We need to halt the progress of these plants and reduce the threat from other potential garden escapees. Plant species that have escaped from our gardens and invaded our bushlands are referred to as environmental weeds.
How do plants become garden escapees?
You may not realise it but your garden could be a source of garden escapees. Many of the plants we grow in our gardens escape to invade our natural bushland. Birds spread seeds after eating berries and fruit and can spread weeds far and wide. Wind and rain also help disperse seeds and the dumping of garden waste into natural areas can spread weeds that grow from corms, bulbs and stems.
Why are garden weeds such a problem?
Garden escapees have the potential to smother or out-compete native plants and therefore drastically change the make up and natural balance of our remnant bushland areas. This can result in serious impacts upon the health and viability of our native wildlife. The uniqueness and special character of our natural areas will be changed and possibly lost forever unless we decide to act now.
Alternatives for garden weeds
With an increased awareness of the need for drought tolerant species, many gardeners are looking to succulents, grasses and Mediterranean plants. Many of these species have the potential to become the next crop of garden escapees. Planting local natives avoids these problems and provides food and habitat for local wildlife.
Originally there were over 850 species of native plants growing across Adelaide, providing a broad range of interesting forms, textures and flowering times. Several of these are be available from local nurseries (check out our native plant growers list) and most survive on little more than local rainfall once established.
Weed fact sheets and more information
We have developed an Environmental Weeds Brochure to help identify and highlight common and very damaging weeds in the Mount Lofty Ranges region. Many of these are garden escapee plants, so take a look and see if you have any in your garden that you need to be aware of.
To access more weed information and species fact sheets, please visit the Adelaide and Mount Lofty Ranges NRM Board webpage featuring Weeds common to the Adelaide and Mount Lofty Ranges Area, Biosecurity SA's brochure on Declared plants of South Australia (580 KB pdf) or Invasive plants in bushland ~ Adelaide Hills District Council. Also see Introduced Flora of Australia and its Weed Potential (528pp pdf).
Top invasive garden plants in South Australia (from www.weeds.org.au)
Aleppo pine (Pinus halepensis)
Desert ash (Fraxinus angustifolia)
Fountain grass (Pennisetum setaceum)
Gazania (Gazania linearis hybrids)
Golden wreath wattle (Acacia saligna)
Kikuyu grass (Pennisetum clandestinum)
Olive (Olea europaea)
Periwinkle (Vinca major)
Topped lavender (Lavandula stoechas)
Weeping willow (Salix babylonica)