How To Remove Japanese Knotweed From Your Property Japanese knotweed has hit the news several times this year due to the damage and invasive nature of the plant. Whilst the plant has a large heart-shaped leaf canopy with beautiful flowers in the summer months, Japanese knotweed is extremely aggressive causing widespread damage to properties. Many mortgage lenders will not lend to properties where Japanese knotweed has been left untreated. To unravel the complexities surrounding Japanese knotweed, we’ve called in the experts to advise us how we can successfully remove Japanese knotweed. Nic Seal, is the Managing Director of Environet UK, specialists in Japanese knotweed removal. Environet was established in 1996 and is a recognised leading UK firm in the fight against Japanese knotweed. We asked Nic to give some insight into the best way to treat knotweed. Will treatments kill Japanese knotweed?
Japanese knotweed is very seldom killed with just one treatment and it usually takes several applications of herbicide correctly applied at the right dose, right time of year and to the right part of the plant. If the application of herbicide is completed incorrectly, for example too much herbicide being applied, this can make the knotweed appear dead above the ground, when in fact it is simply dormant. This explains why after herbicide treatment, regrowth can be experienced for several years after the treatment was applied. It is important that a trained sprayer completes the work, as they will know how to complete it successfully. It is always very difficult to verify with 100% certainty that knotweed has been killed by herbicide, because of this dormancy issue. If some tool could be developed that could see the underground rhizome that would be an exciting development for the knotweed industry! We have experienced Japanese knotweed that has been treated with herbicide (by others), where there was no growth for 10 years, yet when the ground was disturbed during construction
work, the dormant rhizome was reactivated. The knotweed then started to regrow.
In what circumstances is it better to use a Japanese knotweed removal process?
As I said above, with herbicide treatments, you cannot be sure that all the root system is dead; it’s a possibility it’s dormant and can be reactivated at any time by soil disturbance. For that reason, we would say that a removal process is the preferred method where previously infested ground is to be disturbed, eg for construction or landscaping type work. If you simply rely on herbicide treatment and there is viable dormant rhizome in the ground, you will fragment it into many hundreds if not thousands of pieces and each piece will have the potential to grow into a new plant. This means the knotweed will be spread around the plot, making it a much bigger problem. Removal is likely to give a more certain result and will be completed much quicker than a herbicide treatment plan can, as these can take 1 + years to complete. If you’re up against time constraints, for an example in a house sale where the buyer/lender is insistent the problem is dealt with before the sale can be agreed, then removal is the best option.
Can I just dig knotweed out of my garden?
Yes you could do, but you would be well advised not to. The reason for this is that a mature stand of knotweed is likely to have rhizomes extending up to 2m deep. It requires expertise in determining the extent the rhizome system has spread and to identify it in the ground. If you attempt to dig it out yourself, and then ask a specialist to finish off the job, you will find great resistance because it will be very difficult for that specialist to be able to know the full extent of the rhizome because your effort will have potentially fragmented and spread the rhizome. There are laws regarding the disposal of knotweed which need to be considered, you can’t just put it in your green waste. Also if you’re selling your property and your buyer needs a mortgage, the lender will not look kindly on
your DIY treatment, preferring to have a reputable company complete the work and provide an insurance backed guarantee. So in summary, you can, but you’re advised not to because it is risky.
Does Japanese knotweed removal differ between residential and commercial sites?
In principle no, as in both cases all of the knotweed, both above and below ground will be removed. The differences come with the type of equipment that can be used. Commercial sites are much larger in scale, and can fit all suitable machinery such as excavators and our specialist Xtract™ machine. What’s the best method to remove Japanese knotweed?
Historically, physical removal of Japanese knotweed would be carried out by an excavator and the infested material would be loaded into 8 wheel tipper trucks and taken to registered landfill sites. This method, known as Dig & Dump, has proved to be very expensive, and is referred to by the Environment Agency as the ‘method of last resort’. In 2008, we at Environet thought there must be a more environmentally friendly and effective method for Japanese knotweed removal, and the idea for our own Xtract™ removal service was born. It works by processing the soils on site, to separate the rhizome from the clean soil. The clean soil can then be used to back fill the land, rather than having to import clean soil at a further expense. The rhizomes are then taken off to landfill, in accordance with the EPA Duty of Care. This process costs around 50% of the dig and dump method, and can be completed in roughly the same amount of time. It has the environmental advantages of very few lorry movements; it does not require the use of any herbicides and results in zero waste to landfill.
Have there been any knotweed removal cases that have stood out to you?
Yes of course! We had a site in Swansea, where we were removing Japanese knotweed for a major house builder, and health and safety was at the forefront of thinking. The risk assessment carried out by the main contractor didn’t
identify the possibility of unearthing unexploded World War 2 German bombs. But that’s exactly what we found! After some delay to ensure the safe disposal of the bomb, we were back on site and successfully removed all of the Japanese knotweed. We have recently completed a project in Liverpool, where 1500 cu m of knotweed infested soil was processed and certified clean in just 5 weeks with our removal machine. No bombs were found this time luckily! We have also recently been involved in a project where knotweed has been growing out of a chimney 7m above ground. On inspection, the chimney flue was found to be rock solid with Japanese knotweed rhizome, which had grown up through the brickwork. This one probably won the prize for best knotweed damage! Certainly opened our eyes to what can happen when knotweed is left unchecked.
If you are looking for Japanese knotweed advice about DIY treatment, total eradication or removal then speak to the experts at Environet UK at www.environetuk.com