I have written about “blue” perennials and annuals before. Typically, they are not blue - rather they are shades of purple or lavender.
I am trying Scabiosa ‘Butterfly Blue’ again this year because I LOVE the flower and the annual scabiosas are long lasting in bouquets. This cultivar is a perennial, but years ago when I grew the plant, it did not overwinter. I am going to grow and sell it as a “hardy” annual this year, and perhaps with global warming, it will make it to 2019.
‘Butterfly Blue’ (above) won the Perennial Plant of the Year for 2000. It does not like wet soils and needs full sun here in northern Vermont.
By the way, below is a photo of supposedly the same plant offered in a catalog, with a lot of help from photo shop.
A plant with similar blooms that does overwinter, and one that I will offer, is Stokesia ‘Honeysong Purple’ (below). This is a late bloomer and the flower is more aster-like.
Campanula ‘Rapido’ Blue (below) is a new bellflower I will try this year. It is similar to the ‘Clips’ series, but is supposed to bloom earlier and for a longer period.
I always grow ‘Blue Jay’ Pacific Giant delphinium (below) - love the color.
For annuals, the best blues can be found in lobelias, particularly ‘Cobalt blue,’ which is grown from seed or laguna sky blue, which is grown from cuttings.