"...Without doubt Persicaria....Also it can grow almost 2 inches in a week
....."

Must have been having a brainstorm, or just hunger got to me, should read
12 inches a week... yes 1 foot.
If you have a few young ones then a couple of weeks of warm wet weather you
will wonder where all the other plants have gone. They will have been
swamped.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk