Blue Lobelia – Complete Guide to Lobelia Siphilitica

Of all Lobelia species, the Great Blue Lobelia is probably the best in terms of attracting a wide variety of pollinators while still being showy and friendly in residential landscaping applications.  It provides a showy display of purple to blue color in late Summer.  And it is reliable in bringing in an array of pollinators including hummingbirds.

Great Blue Lobelia in bloom

I’ve been growing Blue Lobelia for over ten years and have gained much insight into the best ways to successfully grow this plant. From germinating and saving seed to choosing the best location. But this article will be a complete profile on this showy native perennial, including:

In this article:

What is Blue Lobelia

Blue Lobelia is a long-lived perennial flower native to Eastern North America.  Scientifically known as Lobelia siphilitica, it will grow 2-4’ tall in full sun blooming up to two months beginning in late summer.  Important to wildlife, Blue Lobelia will attract numerous species of bees, butterflies, and hummingbirds.

Blue Lobelia is better for wildlife than it’s more famous cousin, the Cardinal Flower (Lobelia cardinalis).  This is because the more open form of the flower of Blue Lobelia can be pollinated by long-tongued bees and not just insects with a proboscis like butterflies or hummingbirds.  So, if attracting wildlife is one of your priorities and you’re pressed for space, this species is for you.

Native Range of Blue Lobelia

The Native Range of Blue Lobelia covers much of Eastern North America.  From Texas to Colorado/Wyoming, up to Manitoba Canada, and then East to the Eastern Seaboard from Main to Georgia.

Source [1]

Reference Table

Scientific NameLobelia siphilitica
Common Name(s)Blue Lobelia, Great Blue Lobelia, Blue Cardinal Flower
Native Range, USDA ZoneEastern North America, USDA zone 4-9
Bloom TimeJuly to September
Bloom Duration, Color8 weeks bloom duration, blue/violet
Height1-3′ (30-90 cm)
Spacing / Spread12-18″
Light RequirementsFull sun to partial sun
Soil TypesSandy loam to clay
MoistureMoist to medium
Fauna Associations / Larval HostsBees, butterflies, hummingbirds
Source [1] [2]

What are the Benefits of Blue Lobelia


Groupings of Blue Lobelia can make a showy eye-catching display of dark blue to purple color.  The plants will stay erect and look great as long as they receive enough moisture.  ‘Blue’ flowers that are actually blue are not that common, so that further makes Blue Lobelia unique.

A single Blue Lobelia flower in bloom

Moist Soil

Blue Lobelia will grow well in areas where the soil is wet.  In the wild you often encounter it near streams or even dry creek beds as long as the area gets partially shaded.


Blue Lobelia will bring wildlife to you yard.  The nectar produced by the flowers is attractive to long-tongued bees, large butterflies such as the Eastern Tiger Swallowtail, and also hummingbirds and hummingbird moths.

You will see plenty of bumblebee ‘butts’ pollinating Blue Lobelia flowers

Residential Friendly

Due to it being erect as long as it receives enough sun, Blue Lobelia will stand tall and look good right on through it’s bloom period.  Removing the stalk before seed production occurs will also prevent any unwanted self-seeding.  But in my personal experience, self-seeding really isn’t a problem for any Lobelia.

Lifecycle, Grow and Care for Blue Lobelia

Blue Lobelia will emerge in early Spring as small shoots protruding in the soil alongside the previous years stalks. Low basal leaves will grow through Spring into early Summer, eventually forming stalks that will rise above. The spike will bloom from bottom to top for about one month in mid to late Summer.

Seed capsules will replace the flowers about 4-6 weeks after blooming. Seeds from Blue Lobelia can be harvested by cutting the stalk and and drying it in a brown paper bag for a week. Then simply crush the capsules to release the tiny seed.

Sunlight Requirements

Blue Lobelia will prefer full sun (six hours or more direct sunlight per day) or partial sun (4-6 hours of sunlight per day).  If it is completely exposed to the sun, it will need access to moisture.  So, wetter areas are a plus.  In my experience it can also grow in medium or well-draining soil as long as it gets sun in the morning and shade in the hot afternoon. [1]

Soil Requirements

Blue Lobelia will grow in soils such as sandy loam, fertile loam, or clay. [1]

Ideally Blue Lobelia will grow best in fertile soil with organic matter present, which would mimic it’s natural habitat of growing near streams.  But don’t let that dissuade you from planting it in poorer soils.  I’ve grown it for years in former-lawn-turf which is poor and infertile, and it has put on a nice display each year.

Moisture Requirements

For moisture, Blue Lobelia can grow in moist to medium-moist soil.  It is not drought tolerant but can tolerate occasional flooding and survive. [1]

During drought, Blue Lobelia should receive supplemental water. Not doing so can result in sun scorch and damage to the leaves.

Sun scorch on Blue Lobelia leaves


The only maintenance needed for Great Blue Lobelia is to remove the pervious years flower stalks in the Spring, or a couple weeks after flowering if one wants to avoid self-seeding.


Blue Lobelia does not need supplemental fertilizer to grow well and put on a beautiful display.

How to Grow Blue Lobelia from Seed

Growing Blue Lobelia from seed is fairly straight forward.  The seeds should experience a cold moist stratification period and exposure to sunlight in order to achieve high germination rates. [3] [4]

The best way to do this is to simply Winter Sow the seed, as the seeds are so tiny that cold stratification in the fridge would probably have to be completed in the pots with soil.  The seed of Blue Lobelia is so tiny that you probably wouldn’t be able to stratify it on a paper towel nor sand.

Process to germinate Blue Lobelia seed

If you intend to Winter Sow the seed, then you can complete the following steps anytime between November and May.  If you are trying to start the seed during Summer, than you will need to place the pots w/ seed in a refrigerator for at least a couple of weeks to help get a high germination rate.

  • Fill a suitable container with moist potting soil.  The soil should be moist enough that when you squeeze a handful only a few drops of water fall out.  Tamp the soil firm with your thumb.
  • Gently pinch some seed between your index finger and thumb.  Rub your fingers together over the pot and closely watch for seed to fall onto the moist potting soil.
  • OPTIONAL – if starting seed when temperatures are warm, now is when you would place the pots in the fridge for 2-4 weeks
  • Place the container in a location that receives morning sun, but afternoon shade. 
  • Keep the soil moist by misting the seed/soil using a spray bottle or pump sprayer so you don’t wash the seed away.  I find that one thorough watering in the morning is sufficient.  But, should you notice that the container is bone dry in the afternoon, perhaps a second watering later in the morning would suffice.
  • Germination should occur in about 14 days.
  • Once seedlings are developing a set of true leaves, you should now thin the seedlings or separate them.  Our guide on separating seedlings can really help, as we use Cardinal Flower (another Lobelia) as an example!
Blue Lobelia seedlings

How long to establish Blue Lobelia

I have found that if you transplant Blue Lobelia into it’s final location during Spring once the basal leaves are about 1” diameter, then you can expect blooming it’s first year by late Summer. 

How to Save Seed

You can save seed from Blue Lobelia by simply letting the flowers fade on the stalk and collecting the capsules.  About four weeks after blooming the capsules will form and ripen where the flowers previously were located.  You will know they are ready for harvest when the capsules look white/brown and dry.

Simply remove the stalk and place it in a brown paper bag or somewhere that it can dry further.  After another week of drying, simply remove the capsules and gently crush them over a paper plate.  The tiny seed and chaff will fall out of the capsule. 

cardinal flower lobelia seeds and stalk with pods
Cardinal Flower or Blue Lobelia Seeds (Lobelia cardinalis / Lobelia siphilitica)

You can sift the seed through a strainer to try to remove some of the excess chaff.  Then, simply place the fully dried seed in a zip-lock bag.  Store seed in the bag in a cool dry place for up to 2-3 years.

Identification and Characteristics of Blue Lobelia


The stalk is medium green and is generally unbranched. 


Lower leaves on the stalk will clasp while upper leaves will have no stem, but not clasp.  The leaves are alternate up the stalk, ovate, elliptic, or oblanceolate in shape and 2” wide by 5” long.  They are medium to dark green in color and have small hairs sporadically distributed. 


On the stalk is a spike/raceme of flowers that can range between 6” and 24” long (15 to 60 cm).  Individual flowers are approximately 1” long and are pointed upwards about 30 degrees from horizontal.  They are two lipped, but lobed with the upper lip having two lobes while the lower lip has 3 lobes.  This gives the flower the appearance of being 5-petaled, but it is actually just two lips.

Close up of Blue Lobelia blooms

Approximately 4 weeks after blooming each flower will be replaced by a small white/brown capsule that contains a lot of tiny seeds.  It is easy to remove the stalk to prevent any self-seeding by just cutting it shortly after blooming. 

Alternatively, if one wishes to spread the plant, just wait until the capsules ripen and dry out, then remove a few a rub them between your fingers over and area you wish the plant to grow.  You will likely be greeted next Summer by new blooming Blue Lobelia flowers!


Blue Lobelia has a fleshy taproot and sometimes has short rhizomes that produce clonal offesets.   But, this plant is not aggressive.  Do not be afraid of it spreading, as it won’t in my nearly 10 years growing experience.

Wildlife, Pests, and Diseases associated with Blue Lobelia


Blue Lobelia is the total package when it comes to attracting pollinators. It will attract long-tongued bees (with bumblebees being the most frequent visitor). But you will also see hummingbirds, hummingbird moths, and butterflies. The key to attracting pollinators is to have multiple plants! Grow 3 or more to attract more wildlife.

Excuse the poor focus on this picture, but I had to quickly shoot with my phone. But this is a hummingbird and Tiger Swallowtail butterfly visiting one of my Blue Lobelia flowers

Deer and Rabbits

Most mammals avoid eating Blue Lobelia as the foliage has toxic alkaloids. But deer may eat the plant. I can say in my own personal experience, in general deer and rabbits tend to avoid all species of the Lobelia genus.


In general Blue Lobelia isn’t effected by any disease. The lower leaves may turn yellow as the plant ages due to shading by upper leaves or drought.

Where you can buy Blue Lobelia

Blue Lobelia is not typically sold in nurseries, as it isn’t a typical ‘garden friendly’ plant. But it can be purchased at specialty nurseries that deal in Native Plants. You can find native plant nurseries near you on our interactive map.

Where to buy seeds

We have ordered a variety of native flower seeds from Everwilde Farms, which you can order right from Amazon through our link on our RECOMMENDED PRODUCTS PAGE. (We may earn a small commission when you purchase through our links, at no cost to you. This helps support our website.)

Uses of Blue Lobelia

Garden Uses

Blue Lobelia is one of the more versatile native plants to use in a garden.  The only real constraint you have with it is that you should avoid very dry sites.  But this upright flower will be right at home in a formal flower bed, border garden, wildflower meadow, near a pond or stream, or a micro-prairie. 

Even better is that the beautiful blue color contrasts well with just about any other flower.

Companion Plants

There are numerous companion plants that enjoy the same or similar growing conditions as Great Blue Lobelia.  Any plant that can grow in sunny locations with moist or medium-moist soil will do well.

Great Blue Lobelia with Bumble Bee
Blue Lobelia with Cardinal Flower in the background

For some plants that bloom concurrently with Blue Lobelia:

For plants that would bloom before or after Blue Lobelia

Medicinal Uses

Native Americans had over 20 documented uses for Blue Lobelia.  Some examples of their use were an infusion of root given for worms, an infusion used for rheumatism, crushed leaves were used for headaches & fever.  It was even used to treat nosebleeds, croup, and syphilis.  So, it appears that Blue Lobelia was a kind of catch-all to treat many different symptoms. [5]

Find more native plants here


[1] – Lobelia siphilitica, USDA. Accessed 14JUN2022.

[2] – Caruso, Christina M., et al. “Pollinators, herbivores, and the maintenance of flower color variation: a case study with Lobelia siphilitica.” International Journal of Plant Sciences 171.9 (2010): 1020-1028.

[3] – Johnston, Mark O. “Effects of cross and self‐fertilization on progeny fitness in Lobelia cardinalis and L. siphilitica.” Evolution 46.3 (1992): 688-702.

[4] – Baskin, Jerry M., and Carol C. Baskin. “Role of temperature and light in the germination ecology of buried seeds of weedy species of disturbed forests. I. Lobelia inflata.” Canadian Journal of Botany 70.3 (1992): 589-592.

[5] – “Lobelia Siphilitica“. North American Ethnobotany Database. Accessed 20JUN2022

Joe Foster

Hi - I grew up outdoors in nature - hiking, fishing, hunting. In high school I got my first job at a garden center where I learned to garden and landscape. I've been growing plants from seed and designing native plant gardens for over 10 years. I hope to share some of my knowledge with you! You may have seen some of my videos I create on our YouTube channel, GrowitBuildit (more than 10 million views!). You can find my channel here: Additionally I am a wood worker / DIY enthusiast. I enjoy designing/building projects (with hand tools when I can!). I hope to give you some tips and useful information!

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