What it says
Lobelia speaks of modesty and quiet generosity. Each flower is a centimetre across; the effect comes only from number. It makes no sense alone.
The genus is named for Matthias de l'Obel, a Flemish botanist and physician to James I of England.
Two very different plants
Edging lobelia is the annual sold in spring: small, trailing, blue, white or mauve.
Cardinal flower is a metre-tall waterside perennial with scarlet flowers. They share only the genus.
In hanging baskets
Its natural use: it trails and hides the container. It wants coolness — not scorching full south — regular water, and a hard cut back by half in midsummer. Many people assume their lobelia is dead in July when it will return in three weeks after a severe trim.
Lobelias contain lobeline, a toxic alkaloid. The plant is not edible, and ingestion in quantity causes nausea and cardiac disturbance.
What it brings to a planting
A clean blue, hard to find in another annual, which lifts yellows and whites. With white it reads as freshness; with orange it becomes vivid.
our piece on flower symbolism places lobelia among the flowers of number.