This Red Valerian (Centranthus) in our garden is just beautiful.
It has a long flowering season (July - October) & once the flowers have faded, I snip it back to a leaf & it sends out more flowers. We only bought one small plant but more have popped up around the garden in shades of pink where it's self-seeded. It's not invasive though, just pull up where you don't want it. The leaves stay a fresh green, no mottling or fading and at the end of the year, just chop it right back, it's fully hardy.
Our original plant was put at the back of the border in very dry soil & in full sun. I let it grow to about 3 feet tall & simply snip it if stems aren't growing in the right direction. Looking to get my hands on a white version now.
Insects love it too.