On 16/09/2019 21:18, Chris Hogg wrote:
On Mon, 16 Sep 2019 18:33:35 +0100, Martin Brown
wrote:

On 16/09/2019 17:59, David Rance wrote:
On Mon, 16 Sep 2019 12:10:50 Nick Maclaren wrote:

In article ,
Martin BrownÂ* wrote:

Himalayan balsam is becoming quite a problem in North Yorkshire on
stream and river banks wiping out almost everything else and spreading
rapidly. Only Japanese knotweed out competes it. Nettles and rosebay
willow herb both die out after a few years leaving a monoculture.

I have never seen it do that, and I have been looking out for it for
several decades now.Â* I believe you that it is a (very) localised
problem, but it assuredly isn't a widespread one.Â* Every apparent

I can well believe that it is only a local difficulty, but it seems to
be incredibly effective at moving along water courses and colonising the
banks to the near exclusion of everything else unless treated promptly.
Its flowers smell quite nice in the evenings a bit like bizzy lizzies on
steroids the explosive seed capsules pack more of a punch.

monoculture of it I have looked at has turned out to be, on closer
inspection, merely that it dominates the top layer and there is a
wide range of other species underneath it.

Only if you count grasses which do seem to hang on in the margins.

Interesting about rosebay willowherb (or should it be rose bay willow
herb? - I've never been sure). I remember my father pointing out to me
the way that it colonised bomb sites during the second world war
especially in London. Then for most of my life it seemed to have
disappeared only to reappear in the last few years, and for the first
time I have some springing up in my garden.

I remember the rosebay willow herb of my youth being a much more
vigorous invasive weed in Manchester on a sandy soil. On my North
Yorkshire heavy clay it barely survives and is seldom seen in hedgerows
here except on or near railway enbankments.

Are there multiple sorts or is it very sensitive to local conditions?

Aka 'fireweed', from it's habit of appearing on areas recently burnt.

Bees like it, and I've always understood from the time I kept them
that there's a 'lesser' and a 'greater' willow herb, but looking in my
wild-flower book I see there are several in the willow herb family,
and hybrids are common. SRH will be along soon to give the definitive
reply.


Rosebay willowherb is the only British species of the genus
Chamaenerion. Chamaenerion is the sister group to the genus Epilobium,
which contains the rest of the British willow herbs. The great
willowherb, Epilobium hirsutum, is about the same size of rosebay, and
tends to damp habitats, such as ditches and canal banks. There are
several smaller, mostly ruderal (Epilobium montanum also occurs in
woodland), species, which are difficult to tell apart - I can manage two
of them - and some species of wet upland habitats including the New
Zealand willowherb, Epilobium brunnescens. And hybrids are indeed said
to be common - I've only seen the one definite hybrid, but my failure to
identify the other species might well be due to be confused by hybrids.