In article ,
Franz Heymann wrote:
"martin" wrote in message
.. .

Having read all the stuff about the unintentional spread of GM
plants, and seen giant hog weed growing along miles of grass verges,
how can you be careful not to let it escape? Why does it appear some
years and not others?

I have sincere doubts if you have ever "seen giant hogweed growing along
miles of grass verges".

He may well have done - I can't tell you what he has been smoking :-)

To martin:

The reason that you won't have done is that it is not a weed of GRASS
verges. Most conditions that will cause a cover of grass are not what
it likes and, if it does grow well, it will kill the grass. You may
well have seen it along miles of VERGES, but an inspection of them
will show either relatively little giant hogweed or relatively little
grass underneath it. The same applies to many other weeds, incidentally.

You can prevent it escaping only by preventing it from setting seed;
cutting it down once or twice a year without fail will do that. If
it appears in a place some years and not others, I suspect that it is
NOT giant hogweed (which is a perennial), but one of the umbellifers
that can be mistaken for it.


Regards,
Nick Maclaren.