Looks like a Salvia but is it?
It grows as reasonably hardy herbaceous perennial in Hertfordshire, UK, but would no doubt persist above ground in a more gentile climate. Grows to about 2ft, stems square. Leaves are a pale green, fairly smooth, not sticky. I haven't seen it in any of the usual references - Yeo, Clebtsch, Salvia Guy or Robin's site - makes me wonder if it really is a Salvia. When it flowers this year I really must take a closer look at the flower detail to get some botanical clues!