What is Japanese Knotweed?

Japanese knotweed (also known as “Fallopia Japonica”) is a non-native plant species which was imported into the UK during Victorian times. It was originally grown as an ornamental plant and was popular because of its ability to form dense screens.  Japanese knotweed is hardy bamboo-like perennial plant which grows quickly and strongly.  It was not considered a particular problem in the early part of the 20^th Century, but gardeners were warned to plant it ‘with caution’.  In fact Japanese knotweed was sold in many nurseries until the 1930’s.  It was only when knotweed started to spread across the country that action started to be taken.  In 1981, Japanese knotweed was classed as an invasive species of plant, making it an offence to plant or otherwise cause it to grow in the wild. The weed can grow up to 20cm per day and reach four metres in height at peak times. During the winter, the leafy parts of the plant die back, often leaving brown bamboo-like hollow shoots.

Improved transport systems, movement of soil and earth across the country, railways and watercourses have all contributed to the spread of knotweed to most parts of the UK.  It has been said that you are seldom more than half a mile away from Japanese knotweed.  This rapid spread over the latter part of the 20^th Century and early part of the 21^st Century has made it more of a problem to homeowners who have seen the value of their properties fall as a result of its presence.  It is estimated that almost 10% of our country’s rivers are contaminated with Japanese knotweed and the cost to eradicate it would be around £1.6billion. The cost of removing knotweed from the Olympic Park site before the 2012 Olympic Games came in at £70m.

Why is Japanese knotweed a problem?

There has been a lot of hysteria in the press regarding Japanese knotweed.  Reports of it growing through walls and concrete and causing structural damage to property and services have all made sensational reading. It is therefore not surprising that the general public have become very concerned.

Perhaps the first reason for Japanese knotweed being a problem is because it is difficult and expensive to eradicate. However it is possible to manage and control knotweed and remove it from property. Such actions can cost money, and sometimes rely on co-operation with nearby or adjoining land owners, which poses some practical problems.

The second reason is the belief that Japanese knotweed causes structural damage.  However, more recent research is showing that structural damage to property is extremely rare and in fact many other hardy plants and trees can cause more structural damage.

The third reason is probably the main reason.  It is about people’s perception of the plant and more importantly their ability to get a mortgage.  Many mortgage lenders are cautious about lending on property with Japanese knotweed either within the grounds or nearby.  This has led to problems with saleability and value. However, there are signs that the approach by mortgage lenders is softening and there is no reason why a property cannot be a suitable security with a proper control and management system in place.

Should I panic?

Probably not.  It can be stressful to find that you have Japanese knotweed in your garden, but it is becoming more common and a fact of life to many property owners. Treatments are become more widespread, better and more effective, and it is controllable.  It doesn’t cause any more damage to property than some other plants and trees.  Larger firms of surveyors are already trying to make representations to mortgage lenders and their professional bodies to downgrade the hype and adopt a more sensible level-headed approach.

If you have any concerns regarding the presence of Japanese knotweed, or about the general structural integrity of a property you are interested in purchasing, then it is always advisable to have a survey performed by a RICS Chartered Surveyor. At Avery & Co. our team of professional RICS surveyors would be happy to offer any assistance and impartial advice. Get in touch to see how we can help. 

Louise Avery is a Chartered Surveyor and Managing Director of Avery & Co.