The message
from "Mike Lyle" contains these words:

They are propagated from root cuttings about (I think).a foot long.
There are separate male and female plants.


Both plants are female. The one that fares poorly has a tightly knotted
ball of 'ingrowing' roots that never seem to spread like the better one.
I don't know the variety but judging from the bitterness they impart to
the beer they are probably one of the copper 'bittering' style hops
rather than aroma hops.

Root cuttings it shall be, thanks to you both for the replies.

--
Cheers,

Allen