phoebe51:
Sorry to hear of your problem. If compost is not properly
heated it does not kill certain "Bad Bacteria"(Pathogens)
but this would mean death sooner than 2 years later.Are
you sure they are S.coccinea? I have had rosemary and
Salvia greggii have a fungal attack were branches die
but here again in a very short amount of time.That
is in my climate. Where are you in the U.S.A ? Maybe some
other things at work.
Art

Your plants sound like forms of Salvia greggii. Do you have images of them at some link we can go to?

So sorry, have been trying to find a photo of Salvia coccinea blk & rouge so it is on my brain. Yes, it is greggii, in raised bed.Originally I potted it up from 1 gln to 5 gln.Started having problems so after a season moved to bed.Seems like the core soil? didn't get enough water possibly. Nothing really in the way of root growth either. It did flower and I got a seed from it and have started a new plant from it this past winter (winter sown).

First the S.coccinea "Forest Fire" has plenty of images.
I have never seen Black & Rouge in person sounds like the same plant as "Forest Fire".S.greggii 'Moonlight' I have in
clay it took a few years to get established(that was 8 Years ago). I have had it die in pots pretty easy nothing
like what your describing .When we are in fog or prolonged periods of rain I have to use a fungicide on some orange forms to keep them alive. I no longer grow them because of that problem. You may have a root rot problem caused by
the compost not being composted properly.If there is to much compost & not enough coarse sand.Drainage may have caused your problem.
Art

phoebe51, are you related (by marriage or otherwise) to John Sorenson formerly of Fair Oaks, CA?

I was confused by the invitation to see photos on Tagged. I am very wary of being invited to give my email and other information out to web services I am not familiar with, so I did not proceed beyond the subscription page.

I finally figured it out by searching my Salvia enthusiast data base, and made some connections.