Recognising and Treating the Dreaded Japanese Knotweed

Top tips on identifying japanese knotweed through the seasons by expert Nic Seal, founder and MD of Environet UK

Valued for its beauty, Japanese knotweed was brought to the UK in the mid nineteenth century and delivered to Kew Gardens in a box of 40 Chinese and Japanese plant varieties. It spread rapidly across the UK as keen gardeners shared cuttings and disposed of garden waste, but now we understand the vast damage it can do to buildings and the thousands it can wipe off the value of our homes if left untreated.
Japanese knotweed is rife across Cornwall and the south west, but the earlier it is discovered, the easier it is to treat, so how can we spot it? In the autumn, the plant’s growing season draws to a close. The bamboo-like canes turn brown and brittle, which can fool people into believing the plant has died or that their own efforts at treating it have been successful. However, like many plants, the rhizome system beneath the ground is healthy and lying dormant throughout the colder winter months.
In spring, red or purple asparagus-like shoots will appear, quickly turning into green bamboo-like stems which grow at a rapid rate, reaching up to 3 metres in height. Knotweed is fully grown by early summer and flowers in late summer, when clusters of spiky stems become covered in tiny creamy-white flowers. The leaves are luscious green in colour, flat and heart shaped in appearance.
Japanese knotweed can be dug out at any time of year using the environmentally friendly Resi-Dig-Out™ method, which involves digging out the rhizome roots and sifting out every viable piece before returning the clean soil to the ground. An insurance-backed guarantee can then be secured for the treatment which will ensure the property can be bought or sold without difficulty. 

Japanese Knotweed Through The Seasons

All that remains are the canes, which have turned brown and brittle and can easily be snapped off.

March/early April
Red or purple asparagus like shoots appear in the ground.

The shoots turn into green bamboo-like stems which grow rapidly, reaching up to 3m in height.

Rather beautiful luscious green, flat, heart-shaped leaves appear.

Clusters of spiky stems are covered with tiny creamy-white flowers.

The flowers die, the leaves turn brown and fall from the plant. 
For professional help and advice on dealing with Japanese knotweed, please visit

Environet is the UK’s leading specialist in the removal of Japanese knotweed, regularly advising RICS, the NAEA and ARMA and working with major house builders, managing agents and private land owners. All work is underwritten by an ‘A’ rated syndicate at Lloyd’s.
Headquartered in Surrey, Environet operates across the UK and leads the market in researching innovative new removal methods. Environet’s Xtract™ method is hailed as the most natural and eco-friendly solution available to tackle Japanese knotweed, removing the plant within days while avoiding the significant financial and environmental costs of traditional ‘dig and dump’ methods. 
Nic Seal, Environmental Scientist, MD and founder of Environet is regularly called upon to act as expert witness in legal disputes involving Japanese knotweed.