The genus "Lobelia" is made up of as many different species as there are days in the year.
The large genus of annual and perennial plants contains many that are native to North America. The showiest of the perennial natives are the tall red blooming "Lobelia cardinals" and the tall blue "Lobelia siphilitica." These bloom from summer to early fall, like a little acidity, average to damp soil and full to part sun. They are perfect on the edge of woodland near some evergreens.
There is also a new rose pink variety "Lobelia Monet Moment" with three-foot flower spikes in August. Annual, low growing lobelia plants are used to edge garden beds and are available in blues, whites and pinks. English gardens often intersperse this lobelia with annual alyssum to create a lacy romantic effect.
They prefer afternoon shade, and they need to be cut back if they get leggy. Keep them well watered but be sure their spot drains well. They often suck in hot dry summer heat but recover as the weather cools. The intense blue of the annual "Lobelia Crystal Palace" combines well with other plants in containers.
Jo Packham wrote, "If you like flowers, give them. If you love flowers, grow them."