Japanese knotweed is regarded as one of the most invasive, rapidly growing species of weed in parts of the UK. This specific weed thrives and spreads at an accelerated rate, which makes it seem uncontrollable, especially when its growth quickens in the summer months.
When that growth becomes problematic, Japanese knotweed can do more than simply stunt the local flora and fauna in your garden. From withholding mortgage offers, to substantial property damage, the effects of Japanese knotweed range from it being a nuisance to highly challenging.
Certain species of weeds are troublesome, but not all are invasive like Japanese knotweed. Under Schedule 9 of the Wildlife and Countryside Act (1981), it is considered an offence to cause Japanese knotweed to grow in anywhere, especially in the wild. This means you have responsibility in controlling and managing the spread of this weed.
The problem with Japanese knotweed is that the adverse influence can often be an oversight, if it isn’t identified and then expertly controlled. When trying to manage a weed invasion, it helps to understand how the problem spreads.
Identification is vital. This weed is a clump-forming perennial that can spring into tall, sometimes dense, stems that reach 2.1m (or 7ft) in height. This stem growth and renewal is, however, largely motivated by its root structures, or deeply set rhizomes that form and establish underground.
Above ground, and according to the season, Japanese knotweed has distinctive features in its appearance which can make its identification easier. Throughout spring and summer, it can develop cream flowers, large leaves and reddish stems that appear very similar to bamboo. Typically, the shoots will flower in later summer or early autumn, developing up to six inches long and milky in appearance. The thick-ish stems, which quickly scale and grow, share its appearance with a bamboo-like plant.
When it comes to identifying and eradicating Japanese knotweed, understanding the role of its roots are key. Without managing what happens underground, it can limit your ability to effectively contain this invasive weed and prevent it from further spreading.
Japanese knotweed roots consist of a rigid network of rhizomes. These can burrow deep underground and appear as tough, wood-like trunks, which often clump together or collect in larger, densely packed, ‘crowns’.
Rhizomes are identifiable by their dark brown trunks, which, when cut, appear orange on the inside. The nature of its roots, especially when it establishes in larger crowns, makes this weed harder to remove without machinery or more specialist techniques.
Rhizomes describes a modified root system that establishes underground and typically, spread horizontally. They can quickly develop new roots from their nodes and these firm deep within the soil. These have the potential to sprout new stems that can rapidly reach the surface, furthering how this weed develops above ground.
Whereas some weeds spread via seeds, rhizome activity represents a different type of plant reproduction. But experts often associate rhizomes with more thuggish, invasive species of weeds that have a reputation for aggressive and rapid growth. That’s because rhizomes motivate new growth underground, which can then multiply and leave behind fragments for future reproduction. Eradicating and removing the full root system is key to preventing future outbreaks, because it only takes partial, leftover sections for a former rhizome to establish again.
Rhizomes burrow up to 3 metres deep below ground, where individual rhizomes can develop up to 20cm in thickness. Typically, if left undisturbed over a longer period of time, this weed can burrow and firm rigidly underground, even crowning in the soil, or collecting its roots in densely gathered systems. This growth will more likely occur where the weed has the time and availability of space to mature and flourish.
Despite its identifiable appearance above ground, including creamy flowers and thicker stems, Japanese knotweed will spread and develop just as veraciously underground as it can within your garden or the wild. It is particularly troublesome, because when it dies back in the winter, this weed can still develop impressive root systems underground.
Japanese knotweed can develop as a challenge without visibly flourishing above the soil. As this occurs in spring, when the bamboo-like shoots begin to emerge, then the extent of the problem becomes more known.
As the root networks can from burrow and clump, the removal of Japanese knotweed can be trickier than other, non-invasive species of weeds. This often means traditional methods of removal are less effective, especially if it risks leaving behind partials of the rhizomes that can re-establish in the soil.
Professional techniques are advisable when dealing with this invasive weed. Root barriers, for example, blocks and prevents this weed from spreading into neighbouring properties and has been especially effective in halting its spread between residential properties. Other solutions, such as chemical treatments like Stem Injection rely on concentred doses of Glyphosate Herbicide, which are injected into the stem to eradicate Japanese knotweed.
Other advanced techniques, such as detection dogs, have been effective in identifying the presence of Japanese knotweed in areas with restricted access, such as weed remnants buried or burrowed in the subsurface, or covered in other overgrown vegetation.
Largely invisible and aggressive, Japanese knotweed can be tricky to control. Even if you’re a veteran gardener, controlling the problem can seem especially difficult if it’s actively spreading underground. If you try to remove the weed yourself, whether manually or chemically, you may risk leaving rhizomes behind. If this happens, Japanese knotweed will continue to spread.
If you’re worried about Japanese knotweed, or suspect it’s growing in your garden, it’s advisable to seek out specialist removal to fully eradicate the problem.
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