Japanese Knotweed Identification

Why’s identification so important?

The first rule of Japanese knotweed elimination is to be able to recognise whether or not you have it present and active in your location. Flagging up the problem correctly is the starting point in any war raged on the notoriously territory-grasping weed, a real villain of modern horticultural times. The danger of Japanese knotweed to Britain’s homes and wildlife is clear and ever present, but the successful identification of Japanese knotweed paves the way to effectively tackling the problem and ultimately defeating the enemy within many of our gardens and countryside.

This is where we come in. Essentially, the identification process involves literally getting to the root of the potential problem, starting by establishing whether the unidentified flora object is the nasty Japanese knotweed or not. The identification process is performed by trained professionals carefully combing the location in search of the plant’s large green oval-shaped leaves and bamboo-type stem. Although the Japanese knotweed is nothing if not a master of disguise, taking on somewhat differing guises and characteristics throughout the calendar year, which certainly keeps us on our toes as we set about making a positive ID. This is why it needs to be done by the professionals like us who know what we’re talking about. Not everyone out there who claims to do this service is legitimate.

When’s the best time of year to spot it?

In the spring – which witnesses the advent of the fastest growth period - new shoots mark out the Japanese knotweed from the usual green crowd, as it sprouts reddish-purple shoots with rolled back dark green or red leaves. This affords it a look similar to that of asparagus spears, while in the summer months the perennial pestilence offers distinctive branching and hollow, bamboo-like stems with a distinctive zigzag effect and covering of purple speckles. These stems also support green heart-shaped leaves which can readily measure 20cm across.

What’s more, in summer you’ll often see small clusters of white flowers emerge, which certainly help with the identification process. Moving on to autumn, at this time of year the Japanese knotweed leaves will start to turn yellow, much in the same way as the leaves of many trees do, with wilting affecting even the mighty knotweed. Once the winter arrives the knotweed will lie dormant, with the leaves now either fully yellowed or dead and therefore having parted company with the rest of the plant. Be warned though, this doesn’t mean that the Japanese knotweed on your property is dead and gone; it could return with a vengeance.

In winter, the knotweed canes will tend to remain steadfast and take on a more brittle look and feel, whilst generally turning dark brown in colouration. In terms of the best time to spot (what could turn out to be) Japanese knotweed, it would ideally be between mid-summer and early-autumn, as knotweed is at its optimum shape and size around then, having experienced rapid growth spurts of around 2cms a day from the spring onwards. 

Ok, so that’s the when. What about the why and how?

Focusing on the leaves of the Japanese knotweed for authentication purposes, ordinarily they bear resemblance to a heart or spear, tapering off to a point and not necessarily facing each other on the stem. With an obvious green hue and saturation, knotweed leaves can reach up to 200mm in length. Flowering towards the latter part of August and the beginning of September, the Japanese knotweed tends to feature elongated clusters of creamy white blossoms, while the ‘rhizome’ (a horizontally-growing underground stem giving rise to lateral shoots when the time is prudent) are somewhat fragile and can snap with relative ease.

That said, it’s pretty much an unseen threat as it prospers beneath the surface during the winter. As mentioned earlier, the exterior of the canes is dark brown, but the insides are typically orange or yellow under examination. Addressing the signature appearance of the stems of a Japanese knotweed, by and large they mimic the look of bamboo shoots. The stems also comprise of nodes from where leaves first break cover, forming zigzag patterns from the get-go. Before you start to panic, please remember, you needn’t worry if you’re not sure whether the plant which has recently appeared in your immediate neck of the woods is a Japanese knotweed; that’s why we founded JKSL, it’s what we’re here to do.

How can you help me then?

All we ask is that you take a few photographs which concentrate on both the leaves and the whole plant and send them to us, and we can often determine if you’re in the line of Japanese knotweed fire or not. There’s always a chance that the weed you’re looking at isn’t actually knotweed, and instead might well be a case of mistaken identity. There’s a parade of usual suspects which people will fear could be the dreaded knotweed, from dogwood to lilac and poplar to – the admittedly more exotic sounding – houttuynia. Throw in Himalayan balsam, honeysuckle, broadleaved dock, bindweed, and the aforementioned bamboo, and it’s easy to see why it’s best to make use of a professional service trained to seek and destroy Japanese knotweed.

So is all Knotweed bad?

Speaking of other knotweeds that aren’t Japanese knotweeds, it’s worth pointing out that there are actually a number of hybrid plants which stem from the Japanese knotweed. For instance, Japanese knotweed also produces hybrid seed from the pollen of Russian vine, the ornamental garden plant and close relation of Japanese knotweed as it happens, yet a less harmful separate entity on our shores. Colloquially known as ‘mile-a-minute’, its seeds hardly ever evolve into viable plants, not least due to the climate here in the UK; so this hybrid fails to make any impact thanks to its sensitivity to our mild and damp winters.

Another type of knotweed variation is giant knotweed, which also made its journey to Europe due to Victorian folk bringing them back from their travels to grow in botanical gardens closer to home. Despite its fearsome name and notably larger size, it won’t usually have the same structural impact as Japanese knotweed. That said, the aptly-named giant knotweed variation can reach upwards of 4 metres, boasting leaves measuring between 20–40cm long, so it will still bring an imposing presence. JKSL can remove this giant knotweed variation as well as your Japanese knotweed. Other knotweeds in Britain include dwarf and Himalayan types, with smaller height and long, slender leaves, respectively.

Why do I need a professional service? Can’t I just leave it?

No, sadly not. The sooner Japanese knotweed is positively identified, the better the long term prognosis for ridding your property of the quickly entrenched weed. In our experience, catching the infestations stops it achieving the height associated with more mature growth. It’s important to treat it before the rhizome becomes well established.

There are some horror stories of the damage Japanese knotweed has done to both residential and commercial properties, and it’s also worth noting that if you just hack away at it and don’t dispose of it properly, you can actually make it worse. It’s also worth noting, that since the Anti-social Behaviour, Crime and Policing Act 2014, “unreasonable conduct” includes a “failure to act” on the Japanese knotweed on your property.

So, why not make use of JKSL’s identification services? We’ll absolutely give you a reliable and professional identification, as well as the right treatment and removal plans if it is found to be Japanese knotweed on your property. Visit our Contact page to get in touch.