That is one lush lookin Valerian!
Here they, along with hollyhocks, are roadside weeds that pop up in every crack in every scrabbly alley and stoney rubble pile. They bloom like crazy in hot sun with lean soil...sometimes it seems with no soil, just stoney calcareous substrate. If I were to hazard a guess, it is living life in the lap of luxury with your temperate climate and plentiful water. Stress it and see if it doesn't decide to bloom before the world comes to an end.
