In my front yard I planted from seed about 6 different edible flowers last year, including blue cornflowers. I wanted to have experience with them all, both in how to grow them, how to use them in a landscape, and how to use them in the kitchen. I let them all go to seed and since that time, most of them have come back this year. One of the first ones that grew this year was my cornflowers, sometimes called by its Latin name of Centaurea Cyanus, or common names of Bachelor's button, Basket flower, and Boutonniere flower.
These are one of the only flowers that are a true blue color. Blue is my favorite color, so I jumped at the chance of having a blue edible flower. As you can see in the picture, not all of my re-seeded cornflowers are blue, but also come in shades of pink and light purple.
I made the mistake of growing these toward the front of my planting area, since the plants get between 3 to 4 feet in height at their full size, which blocks out my shorter flowers. They would look much better in the back.
The plant looks kind of weedy, and I’ve read that originally it was considered a weed in the United Kingdom from where it originated, though is now pretty rare there. I can understand it becoming a weed, since it was very prolific in re-seeding itself. So, I think it would be best controlled to having a backdrop location, with smaller foreground plants hiding all but the upper portions of the cornflower plant from view, but still allowing the blossoms to be seen.
Only the petals of this flower are edible. I would recommend trying a little before using it in large amounts, since some have reported having allergic asthmatic reactions to the pollen.
The flower petals are more stiff and fibrous, so not something you would want to put in a salad. The floral taste reminds me of roses, but with a little bit more spicy sweetness. It is a good flavor for tea.