In Portugal the situation is not so severe, however the Invasive Species Compendium from cabi.org classes the country as having Japanese Knotweed present in the country but not yet on an invasive scale.

If gardeners and homeowners are vigilant, then steps can be taken to stop this invasive plant from causing damage.

Japanese knotweed is a clump-forming perennial that produces stems that can grow up to a height of 3m or more, at a phenomenal rate. As well as growing fast, it's extremely invasive, reproduces very easily and is difficult to get rid of for good. The above-ground stems grow densely and have an unusual purple speckle, before turning brown and dying back in winter. Small flowers appear around this time of year, but the seeds aren't fertile.

Japanese knotweed reproduces and spreads through its stem, crown and creeping underground stems (called rhizomes) - even a small piece can become a new plant. The plants are capable of breaking through tarmac and weak points in concrete and can damage buildings' foundations, drainage systems and walls. The plants can also increase the risk of soil erosion and flooding, among other problems. Japanese knotweed can even 'play dead' - rhizomes can stay dormant underground for as long as 20 years before producing plants.

Eradicating Japanese knotweed can take several seasons - a specialist contractor should be able to ensure the plants don't come back, which is the tricky bit. However, the soil can contain rhizomes as far as 7m from each plant, making it extremely difficult to remove completely.

Any contractor you use must be qualified to deal with Japanese knotweed. If taken off site, it must be disposed of with great care as it is considered to be controlled waste. Soil containing rhizomes must be buried at least 5m deep and covered with a root-barrier membrane, making it a major undertaking.

Keep aware of Japanese knotweed and take action to protect your garden and home if you find it.