Great Blue Lobelia

Lobelia siphilitica

Description & Overview

A native Wisconsin wildflower, Great Blue Lobelia (Lobelia siphilitica) blooms in late summer with bright blue flowers on tall spikes that attract hummingbirds and butterflies. Sometimes a short-lived perennial, Great Blue Lobelia can self-seed under the right conditions, forming attractive colonies in woodland gardens and rain gardens. Provide moist soil, rich in organic matter, to see this plant thrive. May also be known as Great Lobelia or Blue Cardinal Flower.

Core Characteristics

Mature Height: 2-4 feet
Mature Spread: 2-3 feet
Growth Rate: Perennial
Growth Form: Clumping, with erect flower racemes
Light Requirements: Full Sun to Partial Shade
Site Requirements: Moist to wet soil with plenty of organic matter
Flower: Bright Blue
Bloom Period: July through September
Foliage: Medium Green
Fall Color: N/A
Fruit Notes: N/A

Suggested Uses:

Use Great Blue Lobelia in shade perennial beds, in the middle to back of mixed borders, and in naturalized woodland areas. This plant is suitable for rain gardens, wet meadows, and along streams or ponds, and can tolerate black walnut toxicity.

Wildlife Value:

Great Blue Lobelia is pollinator-friendly, attracting hummingbirds and butterflies, particularly Monarchs, as they love the nectar this beautiful flower provides. Learn more about how to attract monarchs to your yard. It is a host plant to the Lobelia Dagger moth (Acronicta lobelia) and is highly sought after for its nectar by Eastern Tiger Swallowtail (Papilio glaucus) butterflies.

Bumblebees are the most frequent and primary pollinators; however, Digger bees (Anthophora terminalis), Yellow-faced bees (Hylaeus spp.), Green Sweat bees (Augochlorini spp.), and Small Carpenter bees (Ceratina spp.) will often visit. Weevils (Cleopomiarus hispidulus) will feed on the seeds.

Most mammals will avoid nibbling on this plant, as it contains unpleasant-tasting compounds, making it deer-resistant.

Maintenance Tips:

Site Great Blue Lobelia in a moist area in part shade. The plant can tolerate full sun but will require mulching and consistent moisture to ensure the roots stay cool. Amend soil with compost when planting and add organic mulch (shredded bark or leaves) periodically to increase organic material content in the soil.

It is a fairly low maintenance perennial. Plants may be divided every 3-5 years, but it can be short-lived. Cut back flower stalks in late fall if desired and watch for seedlings in spring if spreading is a concern.


It has no major disease or insect issues. Slugs may periodically eat the leaves but prefer Hosta and other plants. Mammals, including deer and rabbits, will generally avoid eating it as well as Lobelia contains an alkaloid called lobeline, which discourages animals from feeding on it. Lobeline is toxic to humans, so be mindful when siting it around children and pets.

It can be a short-lived perennial, lasting only a few years; however, proper mulching and moisture can help prolong its lifespan. The plant can self-seed if conditions are right.

Leaf Lore:

Native Lobelias, including Great Blue Lobelia, were once sometimes called vomitwort due to its use in Native American medicine for its cathartic properties. The specific epithet siphilitica is named for its one-time use as a treatment for syphilis.

Companion Plants:

Pair Great Blue Lobelia with other shade-tolerant plants, such as Astilbes and Lungworts, or with rain garden plants such as Swamp Milkweed or Wild Bergamot (Bee Balm). Cardinal Flower, another member of the Lobelia genus, also pairs well with this plant and provides a nice contrast with its bright red flowers.

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