Lobelia Siphilitica Care: All About Growing Great Blue Lobelia

Lobelia Siphilitica [low-BEL-ee-a, sigh-fy-LY-tih-kuh] is a species of flowering plants in the Campanulaceae family.

Originating from North America, this dicotyledonous plant is known for its unique and fancy, bright blue blooms.

With an upright growth pattern, this distinctive plant is perfect for adding vertical interest to the landscape in a graceful manner.

Flowers up close of Great Blue Lobelia (Lobelia Siphilitica)

Common names for Lobelia siphilitica include:

  • Great Blue Lobelia
  • Great Lobelia
  • Big Blue Lobelia
  • Tall Blue Lobelia
  • Blue Cardinal Flower
  • Virginia Bellflower
  • Vomit Root

If you are wondering where the rather strange name ‘Vomit Root’ comes from, you’d be surprised to know the following fact.

According to the Victorian language of flowers, Lobelia symbolizes malevolence and ill will.

This is probably because, in traditional medicine, parts of Lobelia plants were often used to induce vomiting, hence, the name, Vomit Root.

Lobelia Siphilitica Care

Size & Growth

Lobelia siphilitica is a herbaceous perennial, growing between 2′ – 4’ feet tall on average and spreading up to 2’ feet across.

It features an unbranched, sparsely hairy erect central stem bearing lively green foliage.

The alternate leaves approximately measure 5” inches long and are a maximum of 2” inches wide.

They are either ovate or elliptic in shape and joined to the main stem directly.

Flowering and Fragrance

In late summer or early fall, the Lobelia siphilitica puts on a majestic show of flowers as vivid, bright blue blooms appear at the pinnacle of the green-colored stem.

The flowers which measure about 1.5″ inches each and grow in tightly packed clusters to form racemes about 2’ feet long.

Being a member of the bellflower family, the blooms of the Great Lobelia are tubular in shape.

They are composed of two distinct parts.

The upper half, or upper lip as it is usually called, consists of two sleek and slender, upright lobes whereas the lower lip contains three downward curling, oblong lobes.

The graduated petals are pale blue or almost white in color near the base.

Overall, the Big Blue Lobelia flowers have an attractive appearance and are sure to catch every eye from afar.

Light & Temperature

Lobelia siphilitica is suitable for growth in USDA hardiness zones 4 through 9.

It requires full sun but performs equally well if planted under part shade.

Watering and Feeding

Lobelia siphilitica has intense watering needs especially if planted in dry soils or regions with low humidity.

Water it regularly every week, increasing the frequency and amount during dry spells in order to maintain soil moisture.

Soil & Transplanting

Lobelia siphilitica prefers highly moist soil.

In its native regions, it is a freely-growing and often dominant plant in meadows, swamps and other similar places with boggy soil type.

You will see its blue flowers swaying in wet locations near springs, streams, springs and the likes.

In home gardens, this Lobelia species performs well in a wide range of climates given it’s planted in damp or wet soil.

Loamy and heavy clay soils are well suited for this purpose.

Grooming and Maintenance

Lobelia siphilitica is an extremely hardy and low-maintenance plant.

Deadheading may be required to give the plant a neat look and ensure healthy growth during bloom time.

Depending on your preference and the overall plant size, the plant might require occasional pruning.

However, avoid trimming Lobelia during fall.

How to Propagate Great Blue Lobelia

Lobelia siphilitica is easily propagated from seeds.

Sow the seeds in moist soil under a well-lit spot and provide the necessary care until it germinates.

If growing conditions are optimum, Lobelia siphilitica may self-seed to form attractive colonies.

Great Blue Lobelia Pest or Disease Problems

Lobelia siphilitica is a rabbit and deer resistant plant.

It faces little to no threat from most garden pests and insects and is considered safe from being affected by typical plant problems.

However, slugs and snail may damage the foliage as they love to feed on leafy stalks.

More on –> How to Get Rid of Slugs in the Garden

Lobelia siphilitica is considered to be potentially poisonous.

This is because this species of bellflowers contain lobeline – an alkaloid known to have a similar effect on the nervous system as nicotine itself.

Lobelia Siphilitica Uses

Lobelia siphilitica is a must-have for native plant gardens, woodland gardens, rain gardens, and cottage gardens.

It’s the ideal choice for perennial borders and looks stunning when planted near artificial ponds and lakes.

It makes a fine addition to garden beds and is often used to bring a pop of color to areas under partial shade.

The wildflowers of Tall Blue Lobelia make impressive cut flowers, especially when combined with the red bloom color of its relative Lobelia cardinalis (known by its common species name Lobelia Cardinal).

Lobelia siphilitica attracts pollinators so be prepared to welcome a swarm of butterflies, hummingbirds, and even bumblebees when planting this species in your backyard.