Blue Porterweed

http://www.eattheweeds.com/edible-flowers-part-two/

Blue porterweed is a low growing perennial which blooms year round. Often used as a ground cover, it can also be added to hanging baskets. While considered as a short lived perennial, blue porterweed is will self seed or can be propagated by stem cuttings.Although the flowers on blue porterweed are small and each flower only opens for one day, it attracts a large number of butterflies.