Great blue lobelia, Lobelia siphilitica
 
An easy to grow deep blue fall blooming plant that is always buzzing with action even in shadier parts of the garden.
Blue lobelia blooms from August to October. One plant doesn't fill out much space, with a spread of about 10 cm. So it is ideal for small beds, but it could fill in empty spaces through self-seeding in ideal conditions and looks beautiful in mass plantings.
 
Ecology:
Blue lobelia attracts bees of different sizes that will enter the tubular flowers and collect pollen and nectar. The flowers are most frequented by bumble bees, who are more plentiful at this time of the year because they have established their colonies. 
Lobelia is a host plant for several moth species.
 
Growing conditions:
Lobelia grows naturally in shady shorelines, wetlands and moist prairies. It is easy to grow and thrives in all garden conditions as long as they are not dry and full shade. I grow blue lobelia in moist woodland soil among woodland plants that get 2 hours of evening sun and the blue lobelias are not disappearing, so they can withstand quite a bit of shade.