On 2 Jun, 10:19, Malcolm wrote:
Why do you doubt the identification?

Yeah.

It's not exactly difficult to identify. A common source of couch grass
in borders and rockeries is the
neighbouring lawn as the underground rhizomes can spread several feet.
And how would a layer of gravel under the rocks and soil stop couch
grass invading always assuming the poster actually constructed the
rockery themselves?

Easy tiger. Only a suggestion. Phew .... hot today isn't it?!

There used to be a grass-only weedkiller years ago, but I suspect it has
been withdrawn. Glysophate applied by hand would appear to be the only
method of poisoning it.

[...]