Japanese knotweed is one of the world’s most invasive species, leaving some homeowners unable to sell their homes.
Garden experts from GardeningExpress.co.uk have revealed the five main signs of the weed in an attempt to save Britain’s buildings.
Listed by the World Conservation Union as one of the world’s worst invasive species, the weed’s root system and rapid growth can damage concrete foundations, buildings, roads and paving.
Some UK homeowners have even been unable to sell their homes because of evidence of knotweed on the property.
“To some it can look quite attractive with its creamy white flowers and heart shaped leaves – but before you know it, it’s taken hold and is eating through the walls of your house.
“Japanese knotweed is so invasive that it can grow by a metre a month and can cause damage to your home – but the trouble is it can very easily be mistaken for a shrub by a novice gardener.
“These tips should help Brits identify this pesky plant, but if you’re still not sure, check online or ask an experienced gardener.”
1. Red shoots
New shoots will start to emerge in the spring – these are red/purple and can look a bit like asparagus spears. The leaves are normally rolled up and dark green or red in colour.
As the leaves start to spread out, they’ll become a vibrant green colour and heart/shovel shaped with a point at the tip. Some can be as big as 20cm across and they grow staggered at the stem.
In late summer and early autumn small clusters of white/cream flowers will appear. The clusters grow to approximately 0.5cm wide but up to 10cm long. The leaves will still be apparent and along with the flowers, it will create a dense foliage.
The stems are mostly hollow and bamboo like, with nodes and purple speckles. The general growth habit has a distinctive zigzag appearance. Stems can also grow up to 3 metres tall. In the winter, the stems become brittle.
The rhizomes are the underground part of the weed. If fresh, they will snap easily. The outside is dark brown, and the inside is usually an orange/dark yellow colour. The Japanese knotweed rhizome system can grow to depths of 2 metres and can extend up to 7 metres horizontally from the plant. As little as 0.7g of rhizome can give rise to a new plant – which is one of the reasons this weed can become such a nuisance.