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Great Blue Lobelia (Lobelia siphilitica L.)

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Summary
Range
Habitat
Life Cycle
Uses
Links
Photos

Photo © Elias, CC BY 4.0.

↑Summary

A perennial lobelia with a wide range in Eastern North America, particularly common in the northeast and upper midwest.

↑Range - Expand

Legend	Color
Native
Extirpated
Native or Not Present

This tentative map is based on our own research. It may have limited data on Canada and/or Mexico, and there is some subjectivity in our assignment of plants as introduced vs. expanded. Read more in this blog post.

Although this plant occurs somewhere in each of these regions, it may only occur in a small part of some or all of them.

↑Habitat

The great blue lobelia is found in a variety of partly-sunny, moist-to-wet habitats with rich, near-neutral soil. Natural habitats include openings and borders in bottomland and floodplain forests, moist black soil prairies, wet meadows, margins of ponds and rivers, swamps, and fens. It is occasionally found in openings in rich, mesic forests in coves and sheltered slopes in the Appalachians. It also occurs in anthropogenic habitats including managed edges in bottomland forests, parks or gardens, especially those with bodies of water, roadside ditches, and low, moist areas in pastures. It occasionally forms wild populations in suburban gardens, where its volunteers are likely to escape weeding due to its showy flowers that usually start early enough that people recognize what it is.

It is typically limited to moist to wet conditions, and often found on sites that experience temporary flooding, but it occasionally can move onto mesic sites where it is more transient. It prefers partial sun, but ranges into full sun on the wettest sites, and occasionally ranges into light shade. It is usually restricted to fertile, loamy soils with near-neutral pH, to only slightly acidic. It is limited to sites experiencing some vegetation-removing disturbance, but can be found both in pristine natural habitats only experiencing natural disturbance, usually flooding, as well as anthropogenic habitats with mowing or weedwhacking.

The sites on which great blue lobelia occurs may or may not have dense vegetative growth later in the year, but they are usually more exposed at the start of the growing season. It coexists well both with perennials that exhibit similar heights throughout the growing season, as well as annuals like jewelweed (Impatiens capensis), but cannot survive on sites where the ground-level competition is both taller and evergreen.

This species is probably the most shade-tolerant of the eastern lobelias, and also among the neediest of ideal soil conditions. Among the larger-flowering perennial lobelias, both cardinal flower (Lobelia cardinalis) and downy lobelia (Lobelia puberula) are more tolerant of sandy and acidic soils, and replace this species in the southeastern coastal plain. Lobelia cardinalis tolerates, but is also more restricted to wetter sites, whereas Lobelia puberula ranges into drier sites too but is more restricted to acidic soils. Palespike lobelia (Lobelia spicata) prefers similarly-rich loamy soil, but sunnier, drier conditions. None of these species however grow as tall, and great blue lobelia tends to be more competitive on moist sites with rich, loamy soil and more competing vegetation.

↑Life Cycle

This species is a short-lived perennial. Germination time is opportunistic, and can occur at just about any time of year. Seeds germinate when soil is disturbed and vegetation is removed, leading light to reach the ground. Young plants initially grow only as a basal rosette, and often overwinter in this form, with leaves usually being evergreen.

We could not find information on whether or not this species forms a persistent seed bank, but many other Lobelia species follow a pattern in which most seeds germinate in the first year after distribution, with smaller portions persisting each year so that some seeds are present in a long-term seed bank.

Stems, both on first-year plants and older plants alike, begin growing upright in spring and start blooming in mid to late summer. The bloom period is long, and, so long as conditions are favorable, plants will continue growing a longer flower spike, with new flowers at the top while seeds are maturing lower down on the plant. Under favorable conditions plants continue blooming for about 2 months, often well into fall.

Although plants require soil disturbance to establish, established plants are tolerant of significant competition from surrounding vegetation, and will often grow taller in the presence of competition, pushing up through surrounding plants.

On favorable sites, plants will reproduce vegetatively, with each plant forming multiple basal rosettes clustered a few inches apart; these will each then send up a new stem in the subsequent growing season. This vegetative reproduction can occasionally allow a plant to persist when suitable conditions for it move by a few inches each season, but it cannot persist through larger change. In most cases, this reproduction simply results in a larger clump with more flowering stems.

Plants usually live only about 3-4 years, but can sometimes persist longer. They can be killed by drought, prolonged flooding, the basal rosette being buried too deeply by litter and/or soil deposited by floodwaters, or heavy shade from taller vegetation or a closing tree canopy. Some type of disturbance, often from flooding, is important for removing competing vegetation and allowing this species to persist on a site.

↑Uses

This species is widely cultivated in gardens as an ornamental plant, where it is valued for its showy flowers. In most of its range, it is the easiest of the Lobelias to grow in gardens. It benefits from mulching, but modern landscaping practices, prone to heavy overmulching often carried out in early spring, can often harm this plant by burying its basal rosettes before they begin to grow upward, and can make it less competitive against rhizomatous weeds.

It is frequently used in rain gardens, drainage basins, and wetland restorations. It is a good choice of plant for these uses on sites with rich soil.