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Knotty problem: Managing Japanese Knotweed

What do a landlord, gardener, property owner, council official, construction worker and mortgage broker all have in common?

No, it’s not the start of a (very) strange joke, the answer’s a hatred of Japanese Knotweed, and there’s nothing remotely funny about this knotty problem, which costs the UK over £1.5 billion a year to manage.

We might all be loving the warmer weather, but so is this persistent plant, and whilst you we might be relishing spending time in your garden, noticing a looming knotweed lurking in the corner of your garden would put the dampener on even the jolliest barbeque.

Oh behave, it’s a plant! How bad can it be?

Oh, pretty bad! Left to its own devices Japanese Knotweed grows rapidly and will dominate anything that gets in its way – even property! Classed as an ‘invasive weed’, it is an offence under Section 14 of the Wildlife and Countryside Act 1981 to plant or cause Knotweed to grow in the wild.

The nature of the plant’s growing pattern means that it can exploit weaknesses in construction materials, such as concrete, tarmac and brick, with the spiraling tendrils forcing open cracks in buildings, roads and built-structures. With tenuous roots that can spread up to 7 meters, it is particularly dangerous on riverbanks and railways, where it has been known to cause hundreds of thousands of pounds of damage.

Ah. Not ideal then. So, what am I looking for?

This destructive plant starts its life in early Spring with small, unobtrusive shoots, not dissimilar to asparagus – they will be reddy purple in colour and you may not have paid much attention to this insignificant feature in your garden!

By early summer (around now!) the shoots start to really shoot up, thickening into sturdier speckled stems, and sprouting wide, flat green leaves. Over the course of the summer, you could see these monsters grown up to 3 meters in height – even the least green-fingered person is likely to have raised an eyebrow at this towering intruder by this stage!
White flowers will appear in late summer/early autumn, before the leaves and blooms whither away in winter, leaving the stems looking as if they have died – don’t be lulled into a false sense of security though, your knotty problem will be back in the spring, you can count on it!

Well, it sounds delightful. How do I kill it?

It’s not easy, but it possible! There are plenty of specialist companies who can assist with infestations, and in tricky situations calling in an expert is often the best option. However, if you want to have a go at tackling the blighter yourself, there’s a few methods you can try. Do be warned though, poor management on knotweed can sometimes just lead to you spreading the problem, so weigh up the pros and cons of DIY-ing this particular pickle yourself…

  • Burial: It may sound a little macabre, but digging up and then burying the weed can be an effective method of killing it off. However, you do have to make sure that the excavation is comprehensive and that no shoots or roots are left in situ. The subsequent burial sees the plant encased in a root barrier membrane and buried at a depth greater than 5 meters below the surface – quite a significant depth!
  • Chemical: certain weed killer sprays, specifically those containing glyphosate, are able to tackle Japanese knotweed. Most sprays solutions are applied to the foliage and are most effective during the flowering stages, however it is wise to consider the logistics of when you can manage to square up against such a mammoth opponent. In order to get a clear run at the leaves, make sure you cut away any dry stems (these can be burnt) and do try and get as much spray as possible on the wide, flat leaves. Alternatively, you can launch your attack in the late spring (now!) when the plant is at a more manageable size. It could take a few seasons to eradicate knotweed using the at-home-spray method, however if you call in the professionals they will have access to more powerful zapping technology.

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