In NSW there are many other definitions for weeds too. You may have heard of noxious weeds, environmental weeds, agricultural weeds, Weeds of National Significance (WoNS) and National Environmental Alert List weeds.
These are all different classifications of weeds and interestingly some weeds can be several of these classifications. For instance, serrated tussock is a WoNS, a serious agricultural weed and a declared noxious weed in some parts of NSW. Similarly, alligator weed is a WoNS, an environmental weed, a declared noxious weed in some parts of NSW and is now emerging as an agricultural weed as well.
Controlling weeds is voluntary in NSW except for noxious weeds. If a weed on your property is declared noxious in your area you have a legal responsibility to control it. You can check what weeds are declared noxious in your area and how they need to be managed using the NSW WeedWise database.
Some plants can be weedy in some areas and not others. There are many common garden plants that fit this description (e.g. morning glory and agapanthus). For example a harmless garden plant from inland NSW may become weedy if grown in a garden on the coast. Therefore, care must be taken when bringing plants home to your garden from other areas.
Don't be fooled into thinking that native plants are always a safe option. They can also become weeds when they are grown in areas out of their original environment. A classic example of this is the Cootamundra wattle (Acacia baileyana) which has proven invasive outside of its natural region.
Even popular edible species of plants that are often grown in gardens like olives and passionfruit have become weeds in some areas. They need to be carefully managed to reduce the risk of becoming a weed problem elsewhere.
Generally, a plant has the ability to become weedy if they have any of the following traits:
Further information on weedy garden plants and a tool to help you identify a range of weeds can be found at Weeds in Australia.