The flowers of this lobelia species tend to be small (1/3 inch long) and colored pale blue or white. They often occur in a crowded spike on the upper part of the stem. This spike may be 3-12 inches long. Each flower has a smaller upper lip that is divided into 2 lobes, and a larger lower lip that is divided into 3 lobes. These fuse to form a tubular calyx. There is no noticeable scent from the flowers. A variety of insects visit the flower for nectar and serve as pollinators. The flowers are eventually replaced by seedpods. The latter split open at the top, exposing numerous tiny seeds that are easily distributed by the wind.

The sessile leaves are nearly toothless and vary in shape from lance-shaped to oval. The central stem is often ridged or angular near the flower cluster and reddish and hairy near the base. The plant grows 1-4 feet tall. The plant juices are toxic, but the local deer seem immune to these poisons and will feed on this species. It grows in meadows, fields, and thickets throughout much of the eastern half of North America except for the far north and southern lowlands. Although less showy than the related great blue lobelia and cardinal flower of the bellflower species, the pale-spiked lobelia is more drought resistant after it becomes established. It blooms from June to August with flowers lasting about one month. It is a short-lived perennial. It is also called the spiked lobelia.