Garden House Design are pleased to announce our latest service, the treatment and management of Japanese Knotweed (Fallopia japonica), Giant Hogweed (Herecleum mantegazzianum) and Himalayan Balsam (Impatiens glandulifera).


Japanese Knotweed (Fallopia japonica)
Since it was introduced into the UK as an ornamental garden plant in the mid-nineteenth century it has spread across the country causing millions of pounds-worth of damage to buildings , walls, hard surfaces, drainage systems and watercourses. If left untreated it will spread and infest other properties and could cause landowners to be open to legal action. There is a legal obligation not to cause Knotweed to spread if it is present on your land .It can be spread by rhizome regeneration, this can spread up to 6 metres from the visible growth to a depth of 2-3 metres, and also crown or cut stem material. It does not produce viable seed. If allowed to become established the treatment can become costly, especially for those with time constraints.

Here at Garden House Design it is our aim, wherever possible, to offer potential clients a cost effective on site solution to their invasive weed problems, hopefully avoiding excavation and removal. Although this method provides instant eradication it is costly as all material removed is classed as controlled waste. This includes soil containing rhizome and crowns as well as the cut stems.

Listed below are a list of services we can provide along with a brief description of works associated with these methods of control and eradication (if you require further more detailed information, please contact us and we will be pleased to discuss your individual requirements):

Chemical Treatment.
This method is cost-effective and efficient but can take between 24-36 months for eradication. This time scale can be reduced with mechanical disturbance to the area, fertilisation to encourage growth and carefully timed herbicide application.

Reduced Dig & Chemical Treatment.
A shallow excavation is made to remove the plant and some of the rhizome producing a smaller quantity of material for disposal. The remaining knotweed then produces weaker growth which can be eliminated with herbicide over a period of 12-24 months.

Herbicide and Relocation.
The knotweed is excavated and moved to an area of the site where it can then be treated with herbicide. This method works well on phased developments or where it can be worked into the landscaping scheme. Eradication is again over a 24-36 month period. A cost saving can be made by using on site staff and machinery under our supervision.

On Site Capping.
In some cases it may be possible to cap the area of growth using a specialist root barrier. This requires the surface to be scraped or again a shallow excavation to be made. Removal of waste is minimised but the edges of the membrane area may require herbicide treatment in the future.

On Site Cell Burial.
This method is instant and again a cost saving can be made by using site staff and machinery. We would then supervise the excavation of a cell which would be lined and topped with membrane completely encasing the contaminated material. Areas of soft landscaping are ideal for this along with areas of hard surfacing as long as the cell can be created without the risk of instability or subsidence to anything above.

Excavation & Removal.
This method is instant and totally removes the problem from site and is the favoured method of developers on tight build schedules. However, it is expensive as there is a vast amount of waste that has to be removed to a licensed landfill facility. Again, we can provide staff to supervise works on site by others.

Initial Site Surveys & Site Management.
We will conduct initial site surveys to identify and report on the method, or methods, to solve your invasive weed problems, whilst taking in to consideration the sites programme of works and budget constraints. Wherever possible we hope we can find an onsite solution and cut your costs to this growing problem.

We can also offer help in setting up a management programme for larger sites with more severe infestation. This is favoured by the EA and involves the appointment of a clerk of works to oversee the control of knotweed on site whilst creating an operation manual for the land owner, a management plan, and to make sure all contractors on site are aware of the plan. All relevant information needs to be recorded including the location and method used to treat the areas, contamination issues, location of services, onsite training to builders, trees and TPO’s, herbicide records, waste tracking and legal records and information all need to be included.


Other Invasive Weeds.
Giant Hogweed (Herecleum mantegazzianum). Any contact with this plant can cause severe burns and blisters that can cause photo-dermatitis for many years after exposure. Contact with the eyes may cause temporary or in rare cases permanent blindness. It is subject to the same legislation as Japanese Knotweed. Herbicide eradication.

Himalayan Balsam (Impatiens glandulifera). An invasive species that can spread rapidly due to its ability to propel its seed up to 7 metres in distance and producing around 2,500 seeds per plant. Herbicide eradication.

Common Ragwort (Senecio jacobaea). This plant is the most frequent cause of plant poisoning to livestock. It is covered by the provisions of The Weeds Act 1959 and also the Ragwort Control Act 2003. Eradicated by both manual methods and herbicide.

Our operations are carried out in accordance to the Environment Agency Code of Practice 2006, The Wildlife and Countryside Act 1981, the Environmental Protection Act 1990 and all other relevant guidelines and legislation. All works are backed by our Public Liability and Professional Indemnity Insurances.


Please contact us for further information. Click here to view Garden House Design's main website.