I sowed these last year (autumn). I didn't do anything particular, just sowed in 4inch pots under glass. They germinated without needing any stratification...but have been very slow to grow. They got to around 4inches, with a rosette of lance shaped leaves...and have really not done much since. I have noticed that the leaf nodes are gradually extending, growing a definite stem but doubt I will see any blooming this year. I think they behave a little like a subshrub, inasmuch as they retain a woody framework which, I hope, will bloom next year and thereafter. But yep, so much slower and daintier than purpurea.

Yes, I'm expecting it to be a sub-shrub, and have not pruned it at all after it finished blooming. It only grew to about 14" but did bloom for a long time. I guess I'll sow the seeds in 4" pots as well, thank you HU-618169007.