Japanese Knotweed; When to Attack

Japanese knotweed is a real pest, this alien infiltrator has spread itself right across the UK growing anywhere and everywhere. To match the speed of its growth, this plant is highly tenacious, able to survive just about everything the conventional garden would be able to throw at it and come back the stronger for it. So how do you kill it and when is the best time to attack?

Tackling this plant yourself there are several approaches you could take with varying effectiveness and risks attached. Probably the most effective and least risky approach is herbicides, applied either through spraying or through injection. Another option is to try and dig the Japanese knotweed up, this is fairly risky and likely not to produce results unless done professionally, this is because Japanese knotweed will grow back from very small amounts of the rhizome meaning you have to get the whole plant dug up and then find every single piece. Any soil or parts of the plant are then considered controlled waste, which need to be disposed of properly, which can be costly. The third method is to cut the plant down and then cover it with tarps to stop sunlight getting to it. This method will need a huge amount of work, but doesn’t use herbicides. Keep in mind though, that this method also has the issue of producing controlled waste

As for the time to attack; the answer has to be as soon as possible; Japanese knotweed grows at alarming rates and every day it’s left to its own devices, it’s gaining a stronger foothold in your property. The best times to spray it is any time after it’s started to grow, you can expect it to really kick off growing around May time, so be on the lookout from the end of April. Another factor to consider with spraying is that it’s friendlier to bees if you don’t spray it at the end of the summer when it will be flowering.

Always remember as well, once you begin you need to keep the work up, it can take years to fully eradicate a Japanese knotweed, you need to keep at the work and be ready for when it grows back, wherever it may sprout up.

Knotweeds ~ not all bad

Knotweed is a word that can strike fear into the hearts of many a gardener, homeowner, property developer or frankly anybody who has been unfortunate enough to suffer at the roots of Fallopia japonica, more commonly known as Japanese knotweed. This plant has earned its fearsome reputation through years of insidious growth smothering the gardens of unsuspecting people, ripping up the foundations of their homes and costing millions of pounds each year in the UK alone.

There are however many different types of knotweed, none quite as infamous as Japanese knotweed but many far less fearsome and even pleasant. American bistort for example grows from under 30cm to 1.5m high and looks like a white flowered grass. Like Japanese knotweed it has edible parts to it, however rather than the fresh stems, in American bistort, it’s the roots which are edible, either raw or roasted resembling the flavour of roast chestnuts.

Another interesting knotweed species is the water smartweed, a variation which grows in water looking similar to a lily. The water smartweed also has some edible qualities, though the best bit of that plant is the stems again like Japanese knotweed.

Of course there are the plants in the knotweed family which share the same invasive qualities as knotweed itself does; common knotweed for example, is one that likes to sprout up where it’s unwanted. However, it’s somewhat easier to get rid of than Japanese knotweed removal is, simply pulling it up is fairly effective, especially if you catch it before it produces seeds and failing that it can be stopped with herbicides or covering it over with landscaping fabric and mulch; a far cry from its sibling which punches through building foundations, tarps, tarmac and all manner of structures.

Of course if you do find anything resembling knotweed in your garden, it would be a good idea to check and double check which type of knotweed it is, if it’s the dreaded Japanese knotweed, time can be a big factor, the longer it’s left, the more ground it will cover, whether you can see it or not; the roots can spread several meters out and around any visible stems, so you need to really nip them in the bud. Where possible the best approach is likely to use a herbicide either injected into the stems or sprayed over the leaves. Picking the stems while they are very young can be an effective means of slowing it down, however you need to be very careful of what you do with them, since even small parts of the plant can regrow, and it’s a crime in the UK to cause knotweed to spread. But of course, if in doubt, ask an expert!

Knotweed strikes again

Knotweed has struck again in South London where the discovery of japanese knotweed near a council estate has meant scrapping funding for new trees and plants in the area.

Now the elimination of the knotweed has become a higher priority and since it could take several years to destroy it the plans will have to be put on hold.


Source: http://www.southlondon-today.co.uk/news.cfm?id=40531&headline=Knotweed%20kills%20off%20Camberwell%20estate%27s%20%C2%A310,000%20clean-up%20project

The way to destroy Japanese knotweed.

Japanese knotweed is a very durable plant, and many people have tried and failed to kill it effectively, in fact in a lot of cases they have only prompted it to spread, which is something you really should be mindful of as being classified under the Part II of Schedule 9 in the Wildlife and Countryside Act 1981, as stated in Section 14(2) it's an offense to plant or otherwise cause Knotweed to grow in the wild. This is probably most often seen in incidents of improper disposal.

While only the female plant has been discovered in the UK, meaning its seeds are infertile, it has bred with some other plants and introduced hybrids, although in most cases these don’t survive very long.

Primarily, the way knotweed is spread is by fragments of the weed being carried, since very small volumes of it can potentially grow back, it only takes a few centimetres of the rhizome (root) system to start up multiplying once again. Hence, dumping old dirt from a area that might have been infected, chucking away garden waste incorrectly or picking up contaminated dirt up on your shoe and walking it to other locations. These all are possible methods for knotweed to propagate, but how should you combat it?

Well there are numerous tactics for Japanese knotweed's suppression and they range tremendously. The most common practice for Japanese knotweed is to fight it with weed killers, occasionally squirting the foliage, and also injecting the herbicide directly into the stem, which can also stop herbicides from killing nearby plants. This technique is typically quite slow though, it’s very difficult to eradicate knotweed in a single season and you may need to keep treating the Japanese knotweed for several years consecutively.

Other options include excavation of the site; this is probably the priciest method for Japanese knotweed, but tends to produce final results in the shortest timeframe, in particular where the site is sufficient so that you can bury all of the afflicted earth over 5m down.

A technique which is less commonly seen, is a agricultural technique called top soil steam sterilization. Doing just what its name suggests, it involves injecting the soil with steam jets to kill the rhizomes (and everything else for that matter). However this is still being subjected to testing.

Also, the best approach is to deal with it speedily, the more time the problem is left unchecked, the more costly and time consuming it's going to be to solve. Weed killers are usually the commonest approach for people having a go on their own, and it is certainly the most risk free when in contrast to excavation and (god forbid) trimming it back, which without exceptional care and attention could make matters worse, but remember whenever using weed killers, to verify with the council in advance.

Using a Japanese knotweed removal firm however can be expensive, nevertheless approaches provided by organizations for instance excavation can produce better results and reduced timeframes, which can be required for developers and those with property or homes on the line.

The History of Knotweed in Europe

Japanese Knotweed; a menace to botanists, gardeners and a lot of others who have fallen victim to the tenacious plant. But how did Japanese knotweed get started in its campaign to invade the scenery of the earth? Here is a brief evaluation of the ‘roots’ of knotweed in the western world and how it got to Europe and the United States.

Early records of the plant suggest its discovery around the late 1700s in Japan; however it wasn’t rediscovered in the western world for around 150 years. Then in the early 1800s, it started to be introduced to the west as a cosmetic fodder plant thanks to the speed of development and the density of the vegetation it creates. This made it very good for producing screens in gardens.

The tremendous rhizome system created by knotweed was another feature for the marketers of the plant. While these days, the root design of knotweed and the quantity of root needed to infect another location (around the size of a pea!), is well known and feared as one of the various reasons it’s so hard to eliminate once it takes a hold, but when it was first becoming spread around Europe this root structure along with the speed of growth was used to prevent soil erosion. And to that end, it was highly reliable. This was also one of the reasons that knotweed escaped Europe and was introduced in America.

In the UK however, the release was primarily as a garden plant, the original plants were planted in the 1850s and it was dispersed all over the UK in the following years. By the 1880s it was perceived as "naturalised" in the UK.

The undesirable aspects of knotweed took a remarkably long time to come to light. Only at the end of the 19th century were people realizing the plant started sprouting up in places it hadn’t recently been placed and only in 1905 did the Royal Horticultural Society suggest not to plant it unless it was painstakingly taken care of.

Of course at this point, it was much too late and many gardens had been terribly afflicted with Japanese knotweed. It went on to spread out relatively unrestrained till 1981 after the government brought in legal guidelines to suppress the growth of the plant.

Today estimates of the expenditures involved with Japanese knotweed eradication add up to some 150 million pounds each year in combating the spread of this plant. Past simply being only a weed now, it can cause major damage to properties, foundations and tarmac where it sprouts though. In these cases it is especially tough to get rid of, so if you see knotweed, don’t think it’ll subside, nip it in the bud, with more than secateurs.