On Mon, 21 May 2012 16:04:02 +0100, Stewart Robert Hinsley
wrote:

In message , Pam Moore
writes
On Mon, 21 May 2012 13:13:31 +0100, Stewart Robert Hinsley
wrote:

In message , Martin Brown
writes
On 20/05/2012 19:02, Janet wrote:
In ,
says...

I seem to be overwhelmed by these two this year. Cleavers have always been
around in our garden (South Cheshire) but not to the extent that we have
them now and Rosebay Willow Herb has never been a problem before.

Is the weather to blame? Is there anything I can do to reduce the numbers
next year?

Cleavers are annual; they grow from seed every year then die. With any
annual weed if you prevent them re-seeding into your garden then the
population will eventually dwindle out. It's an easy weed to pull out by
hand.

RWH is perennial and can spread underground as well as by seed; the roots
survive underground in winter and regrow the next year. It also sets a LOT
of seed, so you need to both prevent it flowering, and kill off the roots.

Rosebay Willow Herb is another of these curious weeds that is sometimes
absolutely rampant and a serious menace or elsewhere barely able to eke
out a living. I have never been able to figure out whether there are
different cultivars of it or some soils do not suit it. Seems to be
more likely to go rampant in well drained fertile soils.

The one growing along railway lines is usually pretty rampant. But I
have seen in particularly in gardens up north with heavy clay soils
barely able to put up more than two or three shoots each season and
entirely self limiting in growth. Same for the low growing bindweed
(though not the more brutal common C. arvensis)

Supposedly in the 19th century rosebay willowherb was an innocuous
plant, and it didn't become invasive until the 20th century.

There are three cytotypes - Chamaerion angustifolium (diploid),
Chamaerion platyphyllum (tetraploid) and Chamaerion danielsii
(hexaploid). I wonder whether it's just one of them which is invasive,
and that this one wasn't present in Britain (much) before the 20th
century. [British botanists don't make a distinction between the
cytotypes.]


I acquired the white willow herb a few years ago but it had to go as
it spread like ;mad, but is quite beautiful if you have the space to
let it be rampant.

The white form is usually claimed as innocuous. The local plantsman had
it, and it was well-behaved with him.

I put a chunk of it on my allotment and it spread rapidly, by
underground shoots. I bought it from Derry Watkins at Special Plants,
and she warned me it could be "invasive". It was!

Pam in Bristol