As if Japanese knotweed doesn’t cause enough trouble for our homes, another invasive weed may be lurking in your garden … and it’s even bigger.
Giant knotweed (Reynoutria sachalinensis) is Japanese knotweed’s big brother, often reaching heights of five metres in the summer. Its leaves are larger, too.
Although giant knotweed is a goliath on the invasive species scene, it isn’t as common as Japanese knotweed. Thankfully, it wasn’t as popular with the Victorians and when it first arrived from Asia was planted far less.
Giant knotweed or giant hogweed?
Giant knotweed is sometimes confused with giant hogweed simply because the names are similar. However, giant hogweed is perhaps the UK’s most injurious weed, containing a highly toxic sap. So although giant knotweed won’t cause any lasting physical injury, it can pack a punch in fencing, patios and the like.
Giant Knotweed & Hogweed Gallery
Giant knotweed leaves are larger and longer than Japanese knotweed leaves
Giant hogweed flowers look very different to giant knotweed
What does giant knotweed look like?
Giant knotweed behaves like Japanese knotweed, thriving by rivers and railway tracks. It looks like it too, although the giant knotweed leaves can span 20-40cm and its stems can grow five metres tall.
Also like Japanese knotweed, giant knotweed changes with the seasons. Here’s a breakdown.
- In spring, giant knotweed first emerges from the ground like red asparagus tips. From here, it grows fast.
- In summer, it will tower above nearby plants and will produce clusters of dainty flowers.
- In autumn, giant knotweed’s foliage will begin to wilt and its leaves turn yellow. (At this time, the plant will send its core energy down into its roots so it can hibernate during the winter.)
- In winter, the stems will brown, then pale, and look dead.
Not sure you’ve found giant knotweed? Upload a photo to our identification page.
How is giant knotweed different to Japanese knotweed?
Although giant knotweed and Japanese knotweed share most similarities, there are two things which set them apart. Firstly, and most obviously, the best way to distinguish Japanese from giant knotweed is to compare sizes – giant knotweed is much larger and longer! Secondly, the flowers on giant knotweed have a green hue to their white colour, whereas Japanese knotweed flowers are pure white.
More Giant Knotweed
Giant knotweed growing in residential garden
Large infestation of giant knotweed
Giant knotweed and the law
Like Japanese knotweed, there are laws in place to protect people and their properties from giant knotweed. In fact, Schedule 9 of the Wildlife and Countryside Act of 1981 in England and Wales lists giant knotweed as an invasive species. You can be prosecuted for planting or allowing giant knotweed to spread beyond the boundaries of your land. This means argy-bargy could start with the neighbours - not good!
Bohemian knotweed – the horrendous hybrid
Perhaps the biggest threat giant knotweed poses lies in its ability to breed with Japanese knotweed and produce a monster hybrid. Called bohemian knotweed (Reynoutria x bohemica) this hybrid is stronger, faster and more persistent than either parent. Among the other six knotweed varieties growing in the UK, bohemian knotweed may be considered the worst.
And although scientists suggest this horrendous hybrid may soon be the worst, it isn’t as commonly found in the UK at this time.
Like the rest of its kin, giant knotweed can easily be treated or excavated by professionals. That’s us! Call us to discuss your knotweed removal plan today – 0330 678 1077.
