Erysimum Bowles' Mauve - a perennial wallflower. Remove flower heads as they go over and it will keep flowering for months. Help them out by keeping them fed and watered, especially in a pot like the one in your pic. They tend to get leggy and woody after a couple of years but root easily from cuttings so take one or two (if you can find a non-flowering stem!) so you have a replacement ready.
Posts
It makes it look neater and keeps it flowering for ages.