Salvia candelabrum has got me beat! They germinate easily from seed, grow well through the summer, I even get them through the winter but come the spring they start dying.
This year the same thing has happened. Some were in the greenhouse, some were outdoors. Some were outdoors except for during the cold periods. Some were kept on the dry side (without drying out totally) whilst some were exposed to whatever rainfall came our way.
One does appear to have survived and it was the weakest seedling of them all whilst the one right next to it was one of the first to die. The garden has seen -7°c but they were next to one of the house windows so they were maybe three degrees or so warmer?
Has anyone any tips at all?

This is not the easiest of Salvias in the British climate, I have had the same problems as you have. I find that it will only tolerate a few degrees of frost........say, down to -3C.....but it MUST have amazingly well-drained, gritty soil, it will often die if waterlogged. Salvia interrupta is quite similar, but a bit easier. There are a few forms of S. candelabrum (of course some could be hybrids), best I have seen was in Lynsey Pink's garden some time ago, truly spectacular.

The way it's going it's a good job that you sent plenty of seed! My one survivor (which was outdoors all winter in a dry spot) will get potted up into a sandy/gritty mix. The garden saw -7°c but that spot was probably two or three degrees warmer.
As you say it has the potential to be spectacular so I'll stick with it. And I still have a few seeds left.