Weed Meet Again

Himalayan Balsam

Whilst not as destructive as Japanese Knotweed, Himalayan Balsam (or ‘Impatiens Glandulifera’ for its fancy botanical name) is a major weed problem. It can invade residential gardens but is most commonly a problem on riverbanks and wastelands.

Image courtesy of invasiveweedsolutions.co.uk

What should I look out for?

  • Himalayan Balsam can grow 2 – 3m tall and is relatively easy to identify March – October time, but in winter you should look for hay-like remains.
  • When flowering, it produces clusters of pink (or rarely white) trumpet shaped flowers with wide petals, often with spots or markings inside. The stem is a green / red colour early on in the year but changes to pink / red in the summer months, with side shoots forming off of it. The leaves have finely serrated edges, and the seed capsules (approx. 2.5cm) hang on red stalks – these open explosively when ripe, collectively producing up to 800 seeds, and that’s where the problem lies.

How does it spread?

  • Coupled with the fact that the plant grows rapidly, smothering other vegetation as it goes, the seeds are what spreads the plant. They are easily carried by wind, water and people.

Help! What can I do?

  • Care must be taken to ensure that this plant does not escape into the wild, so keep it on lock down and be careful that you don’t inadvertently spread it yourself.
  • In fact, it is an offence in the UK to plant or allow the species to grow in the wild it is that much of a menace.
  • Consider whether you can get rid of the weeds yourself, either by pulling, digging or suppressing them.
  • If the infestation is just too much, you will have to take care of it chemically with suitable weed killers. A specialist will be able to advise, but weed killers based on Glyphosate are generally considered the most worthwhile here – there is no risk of damage to the roots of nearby plants, meaning your ornamental garden can stay healthy.
  • Treat the weed in the early flowering stage.

Giant Hogweed

A close relation to the common Cow Parsley, Heracleum Mantegazzianum is potentially invasive to other plants and is therefore considered a weed. It should be treated with caution however, as it can have adverse skin effects, such as burning and blistering, on contact.

Image courtesy of rhs.org.uk

What should I look out for?

  • The plant grows tall (hence the name giant), up to and over 3m in height.
  • It looks very similar to cow parsley, with thick bristly stems often blotched with purple.
  • The plants have large – in some cases 60cm wide – white flower heads.
  • Chemicals in the sap can cause Photodermatits or Photosensitivity, meaning if you come into contact with it you could suffer burns, blisters, pigmentation of the skin and scarring. Sounds nasty, right?

How does it spread?

  • The weed is spread by its good old seed, meaning it can be transported by you, the wind or the water.

Help! What can I do?

  • Giant Hogweed is widely distributed in the wild but, whilst there is no obligation to remove it from your private property, it is an offence to cause it to grow in the wild in the UK.
  • You can try and remove the infestation yourself, by pulling, digging or suppressing, as with most weeds. Given the adverse effects that contact with the plant can cause to your skin however, you must always wear protective clothing. Wash any skin that comes into contact with the plant immediately.
  • If tackling the weed by non-chemical means (i.e. your own two hands), pull it around May time, when it has reached a reasonable height but before it has produced its flowering spike. Avoid doing this in sunny conditions – pick a nice overcast day (which shouldn’t be too difficult, given our – ahem – tropical climate).
  • As with Himalayan Balsam, use a weed killer based on Glyphosate as they will kill the roots. Spray any young foliage in May and re-treat, if required, in August or September. Remember that mature plants are likely to need more than one round of treatment.
  • Similar to Japanese Knotweed, Giant Hogweed is a controlled waste so, if taken off site, must be disposed of in licensed landfill sites. If destroying at home, compost or burn it.

Produced By;

Kelly Priaulx

The information in this Coffee Break article is intended for guidance only. The authors cannot accept any liability for any loss or damage which may result from the use of this article.