andrewpreece wrote:

As for setting fire, I only have the seeds and they would
be so much charcoal if I put a match to them. I shall try again
and maybe try various germination regimes ( i.e. wet/dryish,
light/no light, cold soak or raised temperature in a polythene
bag etc. That ought to cover the options.

It is concievable that all you need to do is water them with some wood ash and
water.

Various South Africa semi-desert plants have specific germination inhibitors
that require passage of fire followed by rain before they will let the seeds
germinate. Ensures little or no competition for the seedlings after a bushfire
has cleared an area.

Not heard of it for rosebay willow herb before, but I guess it is possible. Many
of the successful weeds have very long lived seeds with extremely erratic
germination so they can opportunistically germinate when coditions are right.
Poppies on newly disturbed earth is a classic case.

Regards,
Martin Brown