I love this little plant and just bought a few young ones for my window boxes.
Lobelia erinus is the most showy of all lobelias and the most popular as ornamental plant.
It blooms from mid spring to early autumn being a lovely plant in borders, window boxes and hanging baskets.
Lobelia erinus or edging lobelia grows only to 8–15 cm tall, spreading and covering the space with a mass of electric blue flowers.
Numerous cultivars come in a wide range of colors, including white, pink, red, different shades of blue and purple.
My favorite is the purple-blue one with a white spot in the center.
It does best in well-drained soil in full sunlight, but it needs partial shade in very hot environment.
Blue Lobelia inter-planted with Sweet Alyssum and Creeping Phlox, in rock gardens or as ground cover is a breathtaking show in any garden.
For bog and swamp garden, another lobelia species, the Cardinal flower (Lobelia Cardinalis) with bright red flowers is the perfect plant.