INVASIVE PLANTS & PROPERTY

INVASIVE PLANTS & PROPERTY

Most gardens around our homes are filled with a variety of plants, shrubs and trees.  Some of these may have the potential to cause issues, due to rapid spread or health impact.  Whilst these plants may not impact lending criteria, surveyors need to be aware of the potential issues so they can offer appropriate advice when undertaking Home Surveys for purchasers.

Japanese Knotweed

Japanese Knotweed is an invasive plant that was imported to the UK in Victorian times.  Originally merited for its beauty, it is now widely recognised as an invasive species with potential to cause damage to the built environment.

Key traits of Japanese knotweed:

• Red shoots emerge in spring
• Leaves which are shield shaped
• Stems that resemble bamboo canes with purple speckles
• Small, cream-coloured flowers developing towards the end of summer

Japanese knotweed is most commonly found in the following places:

• Residential gardens
• Roadside verges
• Railway embankments
• Riverbanks
• Although this plant has been around since Victorian times it is only fairly recently that it has been perceived as a possible concern for residential surveyors.

It was in 2012 that The RICS brought out an Information Paper on Japanese Knotweed with what was generally known as a “7 metre rule”.  Since then, with greater knowledge and understanding on Japanese Knotweed, the threat to buildings is now thought to be less than initially thought.  The RICS issued new Guidance in 2022 looking at the impact on value due to the loss of amenity space.

Other Invasive Species

There are many other plant species that can spread rapidly or are of concern due to the poisonous nature of their vegetation, seeds or sap.  It is important to note that these plants are not of direct concern when undertaking valuations for secured lending and are not considered to be in any way similar to Japanese Knotweed in this regard.

Some examples are:

Bamboo

Bamboo can be found growing in many areas of the UK, but bamboo is not native to these islands.

There are over 1,400 known species of bamboo found around the world.  Many of these species are native to Asia and East Asia, with a few native to South America.

Bamboo is considered good for helping landscape a garden.  However, it can quickly change to a rapidly-growing nuisance overtaking a garden.

There are two primary types of bamboo, running and clumping.  Running bamboo types are the most potentially damaging, as their rhizome system can expand as far as 10 metres underground.  As they spread the rhizomes can exploit existent failures in structures such as drain runs, paths and patios.

Even though bamboo is not native to the UK, it is not classified as an invasive species.  By definition, an invasive species is "an introduced organism that becomes overpopulated and harms its new environment."  Bamboo is not currently covered by the Wildlife and Countryside Act of 1981.

The control of bamboo can prove difficult and time consuming.  It can be achieved by physical removal, but in the case of larger outbreaks may also require the use of herbicides.  Due to the spreading nature of some varieties, it is important that the plant is suitably managed to prevent it taking over areas where it is not wanted and encroachment onto neighbouring land.

Himalayan Balsam

Himalayan Balsam is an annual plant that grows up to around 2.5m tall.

• The stems are green, with red ridges, hollow and fleshy, with weak, shallow roots
• The leaves are serrated, and grow to 25cm in a whorl shape, almost like a star around the stem
• Himalayan Balsam flowers appear in June and will develop in a range of colours including white, pink and purple
• The flowers are followed by seed pods which, when ripe, open explosively when disturbed

Whilst easy to identify in the summer, Himalayan Balsam is a perennial plant, meaning that the above ground growth dies back in the winter.

Originally introduced to the UK as an ornamental garden plant for its beautiful appearance, Himalayan Balsam has escaped cultivation and can now be seen in most wetland habitats including riverbanks and streams, around ponds and lakes.  When the plants die back each winter, large expanses of riverbanks are left bare, with no protection from rising river levels.  The dying plant material often enters our river systems, this can clog our waterways and cause flooding.

The plant is not harmful to touch or pull manually and isn’t poisonous to horses or any other animals.

Giant Hogweed

Giant Hogweed, native to South-East Asia was imported to the UK as an ornamental garden plant in Victorian times.  Since then, it has escaped from intentionally planted areas into the countryside.

• Giant Hogweed has blotchy purple marks on the stems
• Giant Hogweed can grow 3-5m tall
• Flowers from mid-June to end of July
• The sap of Giant Hogweed is TOXIC
• The seeds of Giant Hogweed can remain viable for up to 15 years

Giant Hogweed leaves are usually dark green and are spiky in appearance, growing in a rosette formation similar to dandelions.  Before it blooms in early summer, each Giant Hogweed leaf can grow to 1.5m in diameter.

Giant Hogweed is probably one of the most well known invasive plants that grow in the UK because of the skin burns and blisters that occur when people get the sap on their skin.

Horsetail

Horsetail is one of the longest surviving plants.  It can be poisonous to livestock, particularly horses if consumed in large enough quantities.

Common Horsetail plants resemble small fir-like trees rather than conventional weeds.  It is a perennial so it dies off almost entirely in the winter months and lies dormant during the cold weather.

Common Horsetail plants quickly build into extensive clusters and take over local habitats if left uncontrolled.  This particular variety of the species is widespread across Britain, often found on roadsides, in gardens, on paths, brownfield sites and wasteland.

Horsetail roots are rhizomatic meaning they can spread quite quickly with the potential to grow and cause problems in the garden.