The world is getting smaller with our capacity to travel and that brings opportunity for trade. The currency of gardeners is plants and since the development of the means for long distance travel, the movement of plants across our planet has continued to accelerate.
European settlers have been responsible for the introduction of many species, some good, and others not so welcome to our fair shores. History is littered with those introduced species that have gained a threshold and out-compete native plants, destroy habitat and can harbour pest and diseases with potentially devastating impacts. Many of these plants have been introduced for their aesthetic appearance or valuable fruits, but that's not to say that they are without their problems.
These invasive plants are well known to gardeners and include plants such as coffee. Some species of coffee can grow in low light levels and have become weeds in some warm rainforest areas of the east coast.
The Brazilian cherry is another that has become invasive in the warm temperate rainforests and should be avoided as a garden plant. Lily pilli is a more appropriate alternative.
Olives are also problematic in some regions.
Cassia is a hardy species that was introduced from South America and is prevalent in a range of habitats making it very undesirable. Cassia produces attractive yellow flowers which made it a popular garden selection in the '70s, but its invasive nature has seen it relegated to weed status.
The trend in horticulture towards using ornamental grasses has given rise to several invasive species. The problem with many grasses is their ability to produce large numbers of seed that are wind-dispersed. Species such as fountain grass and Japanese silver grass can be invasive. However there are cultivars of these plants that are sterile or do not tend to produce as much seed.
Other strap leaf plants such as agapanthus have also become environmental weeds in many regions but with good plant management practices can still be grown by simply removing the developing seed heads before they release seeds.
Local councils for each region will have a list of invasive plant species that should be avoided in the home garden and a substitute list of suitable alternative native species.
The responsible gardener should consider the potential weed status of any plant selected for the garden and choose a native alternative, the benefits to local fauna and the natural environment are well worth the investment.
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