Japanese Knotweed… Ignore this plant at your cost

Tuesday, 19th June 2012 | by: Peter Barry

Over the last couple of years I have noticed that Japanese knotweed has received an increasing amount of press coverage, the reports always seem to have similar characteristics and usually follow the same pattern:

After struggling to save up enough money and seemingly against all odds a young couple view a property, decide it’s the one for them, put forward their offer, go through the normal negotiation and legal hurdles, have their offer accepted, exchange and then quickly move into the property, still excited by their first step onto the property ladder.

Once they have got over the move, and after the usual lick of paint to all rooms, they turn their attention to garden as the plants have become so overgrown they can no longer be ignored, furthermore summer is fast approaching so they want to be ready for the countless BBQ’s they are planning to have.

The garden contains the usual suspects, over grown grass, weeds growing out of every gap in the paving, holly bushes lined with barbs waiting to punish the first novice gardener who sets their secateurs upon it, and finally a rather unusual green and red plant that resembles bamboo, that upon initial inspection is a rather attractive addition to the garden.

After a weekend of sweat and graft the garden is looking better than ever, all the bushes are pruned, the pathway is finally visible and the fresh smell of cut grass fills the air.

However, after a week the couple notice that the bamboo lookalike has not only re-grown but now appears to be growing in new places. Unknowingly they again descend on the garden this time making sure they remove all trace of the plant and again restoring their garden to its new found beauty.

A couple of weeks pass and again to their surprise the couple notice that the plant has reappeared, only this time it is far more vigorous and is even growing through their newly laid paving. Fed up of the constant battle, the couple call in a gardener, he visits and quickly confirms that the plant isn’t bamboo, but is actually Japanese Knotweed. However, more alarmingly, he informs them that its removal will cost thousands of pounds and if left untreated could mean their newly acquired house is unsalable!


Japanese Knotweed has its origins in Japan, hence the name, where it grows freely; the plant was introduced to Britain in the early 19th Century as an ornamental plant after being noted for its attractive appearance. Japan itself doesn’t suffer from the same affects that Britain has with Knotweed, this is mainly due to Japan having native bugs, Aphalara Itadori that control its growth. In Britain this bug isn’t native, therefore there isn’t any form of natural control stemming or stopping its growth.

To the trained eye the plant itself is unmistakable, however to a lay person, it can often be overlooked or mistaken for other plants, the common mistaken identities are, Leycesteria Formosa also known as Pheasant Berry, due to the shape, color and appearance of the leaves or even young/infant bamboo due to the color of the shoots.


The key identifying characteristics of knotweed are as follows;

  1. The leaf is usually a shield/heart shape, the sizes of the leaves vary depending upon the age, however they all retain this characteristic.
  2. The leaf stem will always have a ‘zig-zag’ pattern and will be purple/red in colour.
  3. The stem of the plant is similar to bamboo, however, unlike bamboo there are usually purple specks.
  4. The foot of the stem, also known as the crown, grows partially above ground and often various other stems or roots will be visible.
  5. The flowers, when in bloom, are white and grow in clusters.

Knotweed itself posses such a risk due to its invasive nature and the un-formidable rate of growth, not only does it grow quickly but it also grows through most structures including concrete. Once the shoots or stem has penetrated the concrete, its rate of growth will then increase as it works its way further into the structure eventually forcing it apart often causing severe damage.

Below are two photos taken a week apart, as you can see, the growth is vigorous.

Japanese Knotweed is also considered problematic due to the legislation surrounding it. Under the Wildlife and Countryside Act 1981 it is an offense to plant or cause Knotweed to spread in the wild and furthermore all waste (soil/cuttings) containing Japanese knotweed comes under the control of Part II of the Environmental Protection Act 1990 and must be properly disposed off as it is actually classed as controlled waste.

The second Act is the more relevant one, in part as it is actually an offense that can lead to prosecution if the Knotweed is not properly disposed of. This means that all waste containing the invasive plant must be taken to a licensed premises where it will be properly disposed off, this added cost is one of the reasons the removal of Knotweed is so expensive.

Below is a photo of a bay window, as you can see the Knotweed has grown through the wall and ground, in this case the ground was laid concrete and the bay was solid brick.

When it comes to the control of Japanese Knotweed there are a number of options available, a key point to note is that due to the complicated and difficult nature of the plant, very few companies offer a 100% removal guarantee. There are a number of variants/combinations of removal however in general they fall into the following categories:

Excavation: This option will see all the contaminated soil ‘dug out’ and removed from site, when the soil is removed it cannot simply be sent to landfill as this will only see the problem transferred somewhere else. Instead the soil/waste will need to be placed in a barrier and then sent to landfill. This option is not always available due to the site restrictions, for example, the existence of neighbouring houses. However, it is also a very expensive and intrusive option as all the removed soil will need to replaced.

Herbicide Control: This option involves the repetitive use of herbicides to slowly kill the plant, in some cases the stem of the plant will actually be injected to kill it at its root. This option is by no means a quick solution and can often take months even years to properly eradicate/control the knotweed.

Barriers/Root Barriers: This option is usually used in combination with herbicide control and inves excavating along boundaries and inserting a physical barrier to ensure the plant cannot spread from one site to another. The plant is then contained and can be treated/controlled/eradicated through the use of specialist herbicides.

The above options should only be undertaken by an experienced specialist, as a rule of thumb the removal/treatment of knotweed within a residential circumstance will likely cost in the region of £3,000 – £5,000. Due to the nature of the plant, it practice is far more likely that the control/eradication will be a combination of the above methods as opposed to an ‘off the shelf’ solution.

The likely cost of the removal is a clear indication of the need to take a proactive approach when purchasing a property, by instructing a Chartered Surveyor to undertake a pre-purchase report, such as an RICS HomeBuyer Report or a Full Building Survey. With either of these reports the surveyor will check the property to ensure there aren’t any hidden surprises, such as Japanese Knotweed.

If you think you are a victim of Japanese Knotweed, don’t panic, the first thing to do confirm whether it is Knotweed. Peter Barry Surveyors have worked with specialist companies that are experienced in the control, eradication and removal of Japanese Knotweed and we would be happy to provide a recommendation upon request.

Call Now Button