I have tried to grow this from seed a couple of times. This year the bad weather at Christmas thwarted my attempts. I was in the UK when my little plastic greenhouse was blown over. The
S carduacea had already germinated when I left. On my return I found one pot of waterlogged seedlings all dead. A friend had brought the seeds back from the States for me and, luckily, he had brought some back too for the lady who has an enormous collection of Salvias at
http://www.leessenzedilea.com/. At a recent plant fair she very kindly gave me 2 of the plants she had expertly raised and the first flowers appeared yesterday with more again this morning. With any luck I will have seed to keep these annuals in my garden for many years to come.