Great blue lobelia (Lobelia siphilitica) gets less attention than it deserves. This plant is a member of the bellflower family (Campanulaceae). This family of flowering plants contains well over two thousand species, many of which are familiar garden plants.
This native species provides a dramatic splash of late-season color to your moisture-rich garden plot. While its natural habitat includes woodland stream-sides and wetland borders, you can enjoy a vibrant patch in your native plant garden, woodland garden, or naturalized rain garden.
You’ll definitely want this flower if you want to attract hummingbirds and pollinators to your garden. It will also help increase curb appeal, especially in late summer as your spring and summer-blooming plants are fading, helping extend the growing season or acting as a transition between your summer and fall-blooming blooms.
If you’ve got a bit of space and a moist garden plot, let’s dig right in and get to know the great blue lobelia and everything you need to successfully grow your own.
Great Blue Lobelia Overview
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Plant Natural History
This native wildflower thrives in wet, organically rich soils.
Great blue lobelia is a wildflower native to central and eastern North America, from Canada south to Texas and east to the Atlantic coast. It loves wet environments. You’ll find it growing along streams sides and around swampy edges. It grows near cool springs and in moist meadows. It isn’t too picky about sun or shade as long as it enjoys organically rich, consistently moist soil conditions.
This wildflower inhabits not only wetland borders but can also be found in both woodlands and grasslands. It’s widespread, although not particularly common within its range. This is a valuable wildlife plant, favored by a variety of insect pollinators and hummingbirds. All parts of this plant are mildly poisonous to humans, however, and should not be consumed in any way.
Characteristics
This perennial’s tall, showy flower spikes bloom from late summer to fall.
This native wildflower is an herbaceous perennial. It grows up to four feet tall and up to one-and-a-half feet wide. In ideal conditions, lobelia spreads by self-seeding and root rhizomes, creating attractive colonies without becoming aggressive.
These plants develop several sturdy, upright stems. Each stem is lined with alternate, finely-toothed, lance-shaped leaves of a uniformly green color. They grow vigorously during the growing season and the above-ground foliage dies back completely after the first frost.
Plants begin blooming in mid-to-late summer and continue into early fall, especially in cooler climates. The flower spikes are very showy and dramatic, typically reaching over six inches long. Numerous purplish-blue flowers line the flowering stems, opening from the bottom to the top. Each tubular flower has three prominent lower lobes and two upper lobes that are significantly less pronounced.
Propagation
Propagate by seed or division of mature clusters. If you’re just getting started, you might be able to find great blue lobelia at a nursery specializing in native plants. If you can’t find potted plants, starting from seed is a good way to introduce these plants to your landscape. If you already have lobelia growing in your yard, division is a great way to quickly start new patches of vegetation.
Seed
Sow seeds in the fall and keep them moist for spring germination.
Direct sow seeds in the fall and allow them to overwinter on site. You won’t need to bury the seeds because they need light to germinate, but don’t expect to see any tiny seedlings until after your seeds have overwintered. It’s important to sow the seeds in a location where they will stay fairly moist, particularly in late winter and early spring. Not all the seeds you sow will germinate, but all you need are a few successful seedlings to start a beautiful colony of lobelia plants.
After your seeds germinate in the spring, keep them consistently moist because the young plants are especially sensitive to drying out. Once the seedlings are several inches tall and have developed a few sets of true leaves, you can thin them to one plant per 12 inches or dig and transplant them to the desired location.
Division
Divide perennials in spring or fall for best results.
The quickest and most direct method of propagation is division. The best times to divide your perennials are spring and fall when the weather is a bit cooler, and your plants aren’t in the middle of their peak growing season. All you need is a spade for digging and some comfortable garden gloves to protect your hands.
Either dig out the entire cluster of plants you want to divide or dig around half of the cluster of plants you wish to divide. Using the garden spade, make a clean cut through the center of the cluster so that each half contains both healthy roots and stems.
Re-plant half of the cluster in the same location (if desired) and transplant the other half into a new location. After getting each half settled and surrounded with fresh soil, water each cluster of plants well to help them overcome transplant shock.
Transplanting
Prepare the site and water well after transplanting.
Before transplanting to a new location, first prepare the site. Remove any weeds and other competing vegetation to remove competition. Next, enrich your soil and add any soil amendments, as needed, to ensure that your plants have excellent quality soil in which to grow.
Do your transplanting on a cool day during the spring or fall, avoiding days that are hot, dry, and sunny. Dig a hole slightly larger than the root cluster of your plant. If you are transplanting a potted plant, carefully remove your plant from its pot and immediately place it in the prepared hole.
Fill in around the roots with fresh soil and tamp it down. Finally, water your plant well and keep it well-watered for the first week or so after transplanting to help it settle into its new home.
How to Grow
If you can provide the right growing conditions, this native species is a joy to have in your garden. The most important thing to provide for these plants is rich, moist soil. They are less picky about sunlight; you can grow them in full or partial sun conditions. With ideal growing conditions, you’ll find this lobelia to be easy to grow and virtually trouble-free.
Sunlight
It thrives in full sun, partial shade, or heavy shade.
This wildflower performs well in full sun, dappled sun, and fairly heavy shade. In hotter climates, it prefers some afternoon shade, although in cooler climates, it performs very well in full sun.
Water
It thrives best in consistently moist soil near water sources.
Lobelia siphilitica is a plant that loves constant soil moisture. Ideally, you’ll want to grow it in a location that is either very close to water, such as at the edge of a wetland, or in a low spot that stays moist throughout the year. Be prepared to offer some regular supplemental watering if the soil dries out.
Soil
Plant in rich, moist soil and add compost if sandy.
Plant in a location with organically rich, moist soil. If your soil is naturally sandy, gritty, or other poor quality, add plenty of organic compost to help enrich the soil before planting.
Climate and Temperature
This wildflower thrives in humid summers and cool winters, zones 4-9.
These plants are well adapted to the warm summers and cool winters of the eastern United States and Canada. The species is hardy in USDA Plant Hardiness Zones 4 – 9. Plants go dormant for the winter months and perform well during humid summers. This is not a desert plant and it would not perform well in arid climates.
Fertilizing
Supplement with organic compost if plants show yellowing leaves.
If you have plenty of organic matter in your soil, you shouldn’t need to worry about supplemental fertilizing. If, however, your plants appear weak and the leaves are starting to turn yellow, this may be a sign that your plants need a nutrient boost.
Ideally, add a side dressing or organic compost during the growing season to help improve the overall soil quality. In a pinch, you can add a balanced flower fertilizer. If you use prepared fertilizer products, always follow the instructions on the product label for application and usage.
Maintenance
Cut back dead growth and mulch to protect winter roots.
This is a low-maintenance plant. At the end of the growing season, cut back the dead growth and mulch around your plants to protect the roots for the winter. During the growing season, keep the weeds pulled around your plants to minimize competition. Any time your plants become overcrowded and outgrow their allotted space, you can divide larger clumps and transplant the divisions to new areas.
Garden Design
Add vibrant color and attract pollinators with this perennial.
This dramatic perennial wildflower would make a valuable addition to your landscape. Great blue lobelia is best used where your garden holds moisture or even where you have difficult wet soil conditions.
If you happen to have a pond, wetland, or stream running through your property, this would be an ideal plant to grow along the edge. It’s also a good candidate for a rain garden in a low spot that receives regular moisture and doesn’t dry out. This species isn’t an ideal choice for a raised bed or container garden because it’s difficult to keep these sufficiently moist.
If you don’t have a truly wet area, don’t worry; you can still grow this perennial wildflower. Choose a location with consistently moist soil, ideally with a bit of shade to help keep it cool. Since it is a medium-sized perennial, its size will help it stand out while surrounded by other native perennial wildflowers. Use it to make a dramatic border for your garden, or grow it front and center where its mid to late-season flowers will attract plenty of attention.
The flowers also attract an abundance of pollinators. Do you want to attract hummingbirds to your landscape? Grow a variety of tubular flowers that bloom at different times to attract hummingbirds throughout the spring, summer, and fall. Great blue lobelia blooms later in the season when many of the spring and summer flowers have already finished blooming, so it’s a good choice to extend the feeding season for all your favorite pollinators.
Varieties
Lobelia is a worldwide genus of flowering plants comprising over 400 diverse species. Many are native to tropical locations, including Hawaii, Asia, and Central America. Some Lobelias are native to temperate climates, including a few species native to the United States and Canada.
The following are a few garden-worthy varieties that you might want to consider for your landscape.
Cardinal Flower, L. cardinalis
Brilliant scarlet flowers attract hummingbirds and thrive in moist soil.
Cardinal flower is a spectacular wildflower native to eastern North America. It grows in moist soils along wetlands and streamsides. This plant would be a wonderful companion for the great blue lobelia to enrich your native wildflower garden and hummingbird habitat. Hummingbirds adore cardinal flowers and can’t resist their brilliant scarlet flowers.
Trailing Lobelia, L. erinus
Start seeds in spring for mounding plants with vibrant blue blooms.
This popular annual is easily grown from seed. Start the seeds in early spring and you’ll enjoy mounding plants full of beautiful blue flowers by mid to late summer. Trailing lobelias are a great option for hanging baskets, window boxes, and container gardens where they can fill a small space and cascade over the edges.
Downy Lobelia, L. puberula
This perennial wildflower thrives in dry soils and attracts pollinators.
This perennial wildflower is native to the south-central United States where it grows in moist meadows and grasslands. This species is more tolerant of dry soil than the great blue and is every bit as beautiful. Downy lobelia would make a great addition to your pollinator landscape or prairie garden.
Spiked Lobelia, L. spicata
Pale blue flowers attract hummingbirds and pollinators all summer.
The spiked lobelia, also known as the pale-spike lobelia, is a perennial wildflower native to central North America. It grows in sunny grasslands and adapts well to both dry and moist soils. The pale blue flowers bloom from late spring through mid-summer and attract hummingbirds and numerous insect pollinators.
Wildlife Value
Pretty late-season blooms attract butterflies, bees, and hummingbirds.
This native wildflower will be most appreciated by pollinators, particularly butterflies and native bees. These beneficial insects come to feast on the nectar from within these showy flowers.
And since this plant blooms later in the season than many other summer-blooming flowers, pollinators will benefit from this extended nectar production. Hummingbirds also love the flowers. Great blue lobelia is generally not bothered by deer.
Common Problems
Showy flowers attract butterflies, bees, and hummingbirds late season.
Fortunately, great blue lobelia is not bothered by most pests and diseases. Slugs and snails are an occasional problem, especially when your plants are growing near rocks, fallen logs, and debris that slugs and snails use for daytime shelter.
Slugs are common garden pests that emerge primarily at night. You may never see the slugs that eat your plants, but you’ll certainly notice the damage. Slugs chew holes in the leaves, stems, and flowers of a variety of different vegetation. You may notice irregularly shaped holes throughout the leaves and you may also see the telltale slime trails that slugs leave behind, which appear as glossy meandering lines in the areas around your plants.
Slugs appear most often in damp and humid climates. They hide under rocks, logs, pots, boards, and stepping stones, as well as under decaying leaves and low-growing plants where it’s dark and moist. Deter slugs by removing their hiding places or try using beer traps to remove these pesky pests.
Frequently Asked Questions
Since great blue lobelia loves consistently moist soil and a bit of shade, you’ll want to look for other plants that thrive in these same conditions. If you’re looking for other native perennial wildflowers, try growing swamp milkweed, cardinal flower, or Culver’s root. If you have enough space for a moisture-loving shrub, try growing a buttonbush. All of these plants grow well in the same conditions and also attract hummingbirds and pollinators!
Great blue lobelia occurs naturally throughout most of the central and eastern United States. If you live in these regions, you should have no trouble growing this plant, as long as you have the right local growing conditions. If you live in a western state, you can still grow this beautiful wildflower. It won’t perform well in arid regions or dry soil but if you live in a place with a moderate climate and moist soil, you certainly can grow this lovely perennial.
In ideal conditions, the great blue lobelia will self-seed and form appealing colonies. It won’t, however, grow out of control or become an annoying weed in your garden. It’s quite limited by soil conditions so it naturally won’t spread beyond a plot with moist soil, and it isn’t an aggressive spreader so you can comfortably grow it alongside other wildflowers.
