K wrote:
Martin Brown writes

Some need a bit more warmth than others to get going. High potash feed
and less nitrogen also encourages them to flower as does a bit of
benign neglect of watering. Plants that feel a bit threatened by
environmental stress often flower soon after as a result.

I've given it all the heat that is available, and the tomato feed is of
course high potash. They get the benign neglect by default.

A bit more potash and even less nitrogen maybe.

If you know the species then one of the experts may be able to tell you
what to do to initiate flowering in the UK. My outdoors ones are back
up to flowering size now in N Yorks.

"Back up" to flowering size? - what happened in between?

Cut down by winter frosts. They regrow from the extensive roots (either
in pots or in the ground). My heavy clay soil tends to waterlog in
winter so mostly they live in pots.

"Outdoor" - presumably outdoor summer only? In pots, or in the ground?

No. Winter and summer and regrown again from seed when they fail to
over winter successfully (survive about 4 in 5 winters OK under a 4"
mulch of pine needles).

I wouldn't treat choice plants this way, but since these seem to
tolerate it and still flower...

Their poisonous seeds make excellent rodent bait too.

Regards,
Martin Brown