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Great Blue Lobelia
Great Blue Lobelia (Lobelia siphilitica), also known as the blue cardinal flower, is a native wildflower prized for its striking blue blooms and adaptability to moist garden spots. This herbaceous plant is a short-lived perennial that typically grows in clumping form with upright flower spikes reaching late in the growing season. Great Blue Lobelia produces abundant deep blue to violet tubular flowers on sturdy stems from mid-summer into fall, providing a welcome splash of color after many other flowers have finished. A favorite of hummingbirds, butterflies, and other pollinators, it offers both ornamental beauty and ecological value. As one of the standout blue perennials, Great Blue Lobelia is often used in rain gardens, woodland edges, and perennial borders, especially in naturalistic or wildflower plantings. It has a long history of use in native plant gardens due to its easy care (provided consistent moisture) and its ability to thrive in wet conditions where many other garden flowers cannot. Overall, Great Blue Lobelia is a resilient, native wildflower that brings vibrant blue color and wildlife benefits to the garden in late summer and early autumn.
🌱 Taxonomy and origin
Great Blue Lobelia belongs to the bellflower family, Campanulaceae, and its scientific name is Lobelia siphilitica. The genus Lobelia honors botanist Matthias de Lobel, while the species name “siphilitica” originates from an old medicinal use of this plant in treating syphilis (though it proved ineffective as a cure). Common names include Great Blue Lobelia, blue lobelia, blue cardinal flower, and great lobelia. This species is native to eastern and central North America, found in much of the Eastern United States, Midwest, and parts of southern Canada. In the wild it grows in moist habitats such as wet meadows, stream banks, swampy woodlands, and prairie marsh edges. As a native plant adapted to rich, damp soils, Great Blue Lobelia has become a popular choice for gardeners looking to incorporate native wildflowers into cultivated landscapes. Its natural range and heritage make it a hardy choice for gardens in temperate regions and a fitting companion to other regional natives like Cardinal flower (the red lobelia, Lobelia cardinalis).
🌸 Bloom time
Great Blue Lobelia blooms later in the season, providing color from mid-late summer through early fall. Typically, flowers start opening around July or August and continue well into September, sometimes October, depending on the climate. The bloom period often spans several weeks as the numerous buds on each spike open sequentially from bottom to top. This late bloom time makes Great Blue Lobelia especially valuable for extending the season of blue flowers in the garden after spring and early-summer bloomers (like Forget-me-not or Virginia bluebells) have faded. The flowers are showy two-lipped blue blossoms about 1 inch long, densely crowded along the upper portion of the stem. While individual flowers last only a few days, the long succession of buds ensures a continual floral display for an extended period. Deadheading (removing spent flower spikes) is generally optional – it will not typically prompt new blooms, since Great Blue Lobelia has one main bloom flush, but removing spent stems can tidy the plant or prevent self-seeding if desired. In general, expect Great Blue Lobelia to contribute vibrant late-season color when many other blue perennials are past their prime.
📏 Height and spread
In garden conditions Great Blue Lobelia usually reaches about 2 to 3 feet tall (approximately 60-90 cm) when in bloom, with flower spikes held above a clump of leafy stems. In very favorable conditions (rich soil, ample moisture), plants can sometimes grow taller, up to around 4 feet (120 cm), but 2-3 feet is more common. The unbranched stems are sturdy and upright, so staking is rarely needed. Each individual plant forms a clump roughly 1 to 1.5 feet wide (30-45 cm). The foliage consists of lance-shaped green leaves about 3-5 inches long, arranged alternately on the stem and more densely at the base. Over time, a single plant may slowly enlarge its clump by producing offshoots at the base, but Great Blue Lobelia does not have running roots or aggressive spreading habits. However, it does self-sow readily in hospitable conditions, so a single plant can lead to a small colony as seedlings sprout nearby. In a designed planting, spacing individual plants about 12-18 inches apart is recommended to allow for their mature spread. This spacing will let clumps fill in while still providing good air circulation. Because each plant is relatively short-lived (often living only a few years), the “spread” of a colony is often maintained by new seedlings rather than extensive outward growth of the original plant. Overall, Great Blue Lobelia is moderate in size, fitting well among mid-height border plants and not overwhelming neighboring flowers or shrubs.
☀️ Light
Great Blue Lobelia is adaptable to a range of light conditions, which contributes to its versatility in the garden. It tolerates full sun to partial shade, with the optimal setting depending on moisture and climate. In cooler northern regions or areas where the soil stays consistently moist, Great Blue Lobelia can be grown in full sun (6+ hours of direct sun) and will bloom profusely. In hotter climates or drier sites, however, full sun can cause stress; in those cases the plant appreciates partial shade, especially during the hottest part of the day. Dappled sunlight or morning sun with afternoon shade is often ideal in warm regions, helping to keep soil and roots cooler. Notably, Great Blue Lobelia can handle relatively shady conditions (it is sometimes found in open woodland or the north side of buildings) – it will grow in light or open shade and still bloom, though extremely deep shade may reduce flowering. Essentially, as long as moisture is adequate, this lobelia can thrive from bright sun to half shade. Gardeners should note that in full sun exposure, the soil must remain damp; if a sunny site tends to dry out, consider irrigating regularly or adding mulch, or instead plant Great Blue Lobelia in a part-shade location. Its flexibility with light makes it suitable for various garden niches, from woodland garden settings under high canopies to sunny pollinator garden beds, provided its water needs are met.
💧 Water
Water is a critical factor for Great Blue Lobelia – it loves moisture and does not tolerate drought. In the wild it naturally grows in soggy or seasonally wet areas, so it performs best in gardens with consistent soil moisture. Medium to wet soil is ideal. This plant can even handle standing water or flooded conditions for short periods (making it excellent for rain gardens and pond edges), but it will suffer if the soil dries out completely. Gardeners should aim to keep the soil evenly moist at all times; do not allow the ground around Great Blue Lobelia to become parched. If rainfall is inadequate, provide supplemental watering, especially during summer heat or prolonged dry spells. A layer of organic mulch can help retain soil moisture and keep the roots cool. When newly planted, regular watering is essential to help the plant establish. Even once established, Great Blue Lobelia will wilt quickly in dry conditions and repeated drought stress can be fatal. Signs of insufficient water include drooping or scorched leaves (often the lower leaves will yellow or brown if the plant is too dry). By contrast, the plant is very comfortable in wet sites where other perennials might rot – it can be planted near downspouts, at the edge of streams or ponds, or in low-lying garden sections that stay damp. Because of this preference, Great Blue Lobelia is a top choice for rain garden designs and boggy soil areas. Just remember that in average garden soil, you will likely need to water frequently to mimic the constant moisture of its natural habitat. As long as its “feet” stay wet, this lobelia will remain healthy and lush throughout the growing season.
🌍 Soil and pH
Great Blue Lobelia thrives in rich, fertile soils that retain moisture. The ideal soil is a loam or silty loam high in organic matter (humus), which holds water well but also has some drainage. In practice, the plant is quite tolerant of soil types as long as adequate moisture is present – it can grow in clay soils, mucky or sandy loams, and even clay-heavy sites that many plants find challenging. Good organic content is beneficial, so amending planting areas with compost can improve both water retention and nutrients. Regarding soil pH, Great Blue Lobelia is not very picky: it does well in slightly acidic to neutral soils and even tolerates mildly alkaline conditions. A pH anywhere roughly in the 6.0 to 7.5 range is suitable, and it can handle soils a bit outside that range if other conditions are favorable. Extremely alkaline soils (very high pH) are less common in its native range but as long as moisture is ample, pH is usually not a limiting factor. One thing the soil must not be is extremely dry or drought-prone – fast-draining sandy soil will need amendment and frequent watering to keep it moist, and rocky or compacted dry sites are unsuitable. If planting in heavier clay, ensure there is consistent moisture; Great Blue Lobelia can handle clay provided it stays damp (clay actually holds water well) and doesn’t completely waterlog in winter. The plant’s roots are relatively shallow and fibrous, which means they appreciate loose, friable topsoil but can struggle if soil becomes rock-hard. In summary, give Great Blue Lobelia a nutrient-rich, moisture-retentive soil, and it will adapt to most pH levels and textures. It’s an easy-going plant about soil chemistry, as long as it has the water it needs.
❄️ USDA hardiness
Great Blue Lobelia is a cold-hardy perennial across a broad range of climates. It is generally rated for USDA Hardiness Zones 3 through 9. This means it can survive winter low temperatures down to about -35°F (-37°C) in the colder zones. In practice, many references list it as hardy to at least Zone 4, but it has been successfully grown in parts of Zone 3 with sufficient snow cover or protection. In Zone 3 (northern parts of the US and southern Canada), mulch and site selection (such as avoiding exposed windy spots) can help the plants overwinter more reliably. Throughout Zones 4-9, Great Blue Lobelia typically overwinters without special care, dying back to the ground in late fall and re-sprouting from the crown in spring. At the warm end, in Zones 8-9, it can handle the heat as long as soil moisture is abundant; the limiting factor in hotter climates is often not winter cold but rather summer drought or excessive heat if not shaded or watered enough. Because it prefers cooler, moist environments, extreme southern or desert regions (Zone 10 or above, or Zone 9 with arid conditions) are usually not suitable, unless grown as a short-term plant or in a boggy, shaded spot. In its native range (which spans much of Zone 4-8), it’s well-adapted to the seasonal cycles. When planted within appropriate zones, Great Blue Lobelia doesn’t typically require mulching or insulating for winter (except possibly in the fringe cold zones). However, one consideration in cold climates is frost heaving: because the plant’s roots are shallow, the freeze-thaw cycles of winter can push the crown upward. To prevent this, applying a layer of mulch after the ground freezes can help stabilize soil temperatures. In summary, this species is reliably perennial in most temperate regions, able to withstand significant cold, and its main needs to survive winter are adequate moisture before ground freeze (to avoid desiccation) and perhaps mulch to guard against heaving.
🌼 Propagation and longevity
Great Blue Lobelia can be propagated by seeds, division, or cuttings, and it has a tendency to self-propagate in the garden through self-seeding. Starting from seed is a common method: the seeds are tiny and require a period of cold stratification to germinate well. Gardeners often sow the seeds outdoors in fall or early winter, allowing nature to provide the cold period, or they stratify seeds in the refrigerator for about 6-8 weeks before spring sowing. Sow the fine seeds on the soil surface (they need light to germinate) and keep them moist. With patience, seedlings will emerge and can be grown on to flowering in a year or two. Once established, Great Blue Lobelia frequently self-sows, dropping seeds around the parent plant each fall. If those seeds land on receptive, bare soil, you may find volunteer seedlings the next growing season. This natural reseeding often helps replace older plants, since individual plants live around 3 or 4 years on average. In terms of vegetative propagation, mature clumps can be divided. The best time to divide is early spring, just as new growth begins. Carefully dig up the clump and you will often find several shoot crowns that can be separated and replanted. Division not only creates new plants but can reinvigorate an older clump that may be declining (because the species is somewhat short-lived, dividing every few years can extend its presence). Another propagation option is taking cuttings: in mid-summer, before or just as flowering starts, you can take 4-6 inch softwood stem cuttings from vigorous non-flowering shoots (if available) and root them in a moist medium. Cuttings can be a bit tricky due to the plant’s preference for high moisture; maintaining humidity and shade for cuttings improves success rates. Longevity of Great Blue Lobelia in the garden is often improved by these propagation practices – since a given plant might only live a few years, allowing it to self-seed or periodically dividing it will ensure you have successive generations and continuous presence. If left entirely alone, a colony might dwindle after several years if new seedlings don’t establish, but with minimal effort the stand can perpetuate itself. In summary, expect an individual Great Blue Lobelia plant to be at its best for 2-4 years, but thanks to easy propagation and self-sowing, a well-sited patch can persist indefinitely in the garden.
👃 Fragrance
Despite its showy and abundant flowers, Great Blue Lobelia is not known for having any notable fragrance. The blossoms do not produce a strong scent detectable to humans. This is not unusual, as many blue or tubular flowers rely on visual appeal and nectar for pollinators rather than fragrance. Hummingbirds, bees, and butterflies are drawn to the vivid color and the rich nectar of lobelia flowers, so there hasn’t been evolutionary pressure for this plant to develop a perfumed scent. When you sniff a Great Blue Lobelia bloom, you will likely notice little to no aroma. This makes the plant suitable for gardeners who are sensitive to floral fragrances or who prefer a scent-free flower in the garden. However, if you are looking for a sweet-smelling garden, you’d want to pair lobelia with other fragrant flowers because lobelia won’t contribute a scent. It’s purely an ornamental and ecological contributor rather than an aromatic one. The lack of fragrance does not diminish its garden value, given its vibrant color and wildlife attraction, but it’s good to know that planting Great Blue Lobelia will not add perfume to the air. In cut flower arrangements as well, its tall blue spikes offer visual interest but won’t provide fragrance. Essentially, Great Blue Lobelia’s beauty lies in its appearance and pollinator appeal, not in any smell.
⚠️ Toxicity and pet safety
All parts of Great Blue Lobelia (and lobelias in general) are considered toxic if ingested by humans or animals. The plant contains alkaloid compounds (such as lobeline) that can affect the nervous system and gastrointestinal tract. Toxicity symptoms from eating lobelia plant parts may include nausea, vomiting, diarrhea, excessive salivation, a rapid heartbeat, tremors, and in severe cases, more serious effects. Fortunately, cases of poisoning are rare because the plant’s taste is reportedly quite acrid and animals tend to avoid it. Great Blue Lobelia is deer resistant and rabbit resistant – grazing animals usually leave it alone due to its unpalatable chemistry. In fact, its toxicity is one reason it can flourish in the wild without being heavily browsed. Pet safety: While cats and dogs are not generally attracted to lobelia, if a curious pet were to chew on it, it could cause them to drool or vomit. Pet owners should be aware that Lobelia is listed as a toxic plant for dogs, cats, and other domestic animals if consumed. Luckily, most pets don’t show much interest in munching on this plant. It is still wise to plant it where pets (or young children) won’t be tempted by its leaves or flowers, and if you suspect a pet has ingested any part of it, consult a veterinarian. Handling the plant (touching leaves or flowers) is not irritating, so gardening around it is safe – just remember to wash hands after handling any garden plant, and certainly avoid consuming it. Historically, Lobelia species have been used in herbal medicine in controlled, small doses, but self-medication is dangerous and not advised because of the narrow margin between therapeutic and toxic amounts. In summary, enjoy Great Blue Lobelia’s beauty but treat it as a poisonous plant – admire, but don’t ingest. If you have livestock, note that it can be toxic to grazing animals like cattle or horses as well, although it’s not a common forage plant. With basic precautions, Great Blue Lobelia is a safe addition to landscapes (and again, its toxicity has the benefit of making it naturally pest-resistant from large herbivores).
🌿 Vase life
Great Blue Lobelia can be used as a cut flower, and its vase life is moderately good for a wildflower-type perennial. The tall spikes of blue blossoms add a striking vertical accent to floral arrangements. When cutting Great Blue Lobelia for the vase, it’s best to harvest the stems when roughly one-third to one-half of the flowers on the spike have opened (with the remainder still in bud). Using clean scissors or pruners, cut the stem near the base and immediately place it in water. Strip off any leaves that would be below the water line to reduce decay. In the vase, Great Blue Lobelia’s flowers will continue to open from the bottom upwards over several days. You can expect the cut stems to last around 5 to 7 days in fresh condition, which is fairly decent longevity. The individual tubular flowers are somewhat delicate, so ensure the arrangement is placed out of direct sunlight and heat to prolong their freshness. Changing the water every couple of days and recutting the stem ends can also help extend vase life. Keep in mind that the stems contain a sticky or milky sap (like many lobelia and campanula family members) which can cloud the water; regular water changes mitigate this. While Great Blue Lobelia is not a very common florist flower, gardeners will find that a few spikes mixed into bouquets bring a lovely pop of blue and pair nicely with yellow or white flowers. The spikes hold their shape well and don’t wilt quickly as long as they have water. As the top buds open, you may remove spent lower flowers to maintain a neat look. Overall, in a cut arrangement, Great Blue Lobelia performs reasonably well – not as long-lived as some woody cut stems, but certainly sufficient for enjoying its beauty indoors for nearly a week. It’s a nice bonus that a plant primarily grown for garden color can also double as a cut flower for casual bouquets.
🐛 Pests and diseases
Great Blue Lobelia has the advantage of being relatively trouble-free when it comes to pests and diseases. In healthy conditions, it doesn’t suffer from any major or commonly fatal plant diseases. Its biggest pest issue tends to be slugs and snails, which are attracted to the moist environments this plant prefers. In a wet or shaded garden bed, especially in spring, slugs may chew irregular holes in the foliage or even clip off tender seedlings. Gardeners should monitor young lobelia plants for slug damage and use organic slug controls (like iron phosphate baits or beer traps) or barriers if necessary. Aside from mollusks, few insects bother Great Blue Lobelia. It is not a favored food for deer or rabbits (thanks to its toxicity), and there aren’t specific insect pests that target it significantly. Occasionally, generalist feeders like aphids might appear on flower spikes, but this is not common.
In terms of diseases, the plant can in some cases experience fungal issues such as leaf spots, mildew, or root rot, but these are typically a result of improper siting (for instance, poor air circulation or soil that is stagnant and waterlogged without drainage). Because Great Blue Lobelia likes moisture, it’s often planted in damp areas – ensuring some airflow and not overcrowding plants will help avoid foliar fungal spots. If planted in too much shade with constant wetness, powdery mildew or other molds could develop on leaves, though serious outbreaks are infrequent. Proper spacing (about 1 foot apart or more) helps keep foliage healthy. Another potential issue is crown rot or root rot if the soil is excessively wet and muddy in warm weather, but generally the plant’s love of wet soil means it can handle conditions that would cause rot in less adapted species. Cold climates present a different challenge: the shallow roots can heave out of the ground during freeze-thaw cycles, potentially damaging the crown – but this is a physical issue rather than a pest or disease, and can be prevented with winter mulch. Overall, gardeners will find Great Blue Lobelia to be a low-maintenance plant concerning pests and diseases. It doesn’t require routine spraying or intensive monitoring. By planting it in appropriate conditions (moist soil, not too cramped, partial shade if very hot) and keeping an eye out for slugs, you can expect minimal problems. In fact, many people value this lobelia for its resistance to common nuisances: it’s one of those native wildflowers that, once established, tends to thrive without much fuss, as long as its thirst is quenched.
FAQs
Is Great Blue Lobelia an annual or perennial?
Great Blue Lobelia is a perennial plant. It behaves as a short-lived perennial, meaning each individual plant typically lives for a few years (often around 3 years), rather than indefinitely. It survives winters within its hardiness range by dying back to the ground and re-sprouting from the roots or crown in spring. Because it’s relatively short-lived, gardeners often allow it to self-seed or they divide clumps to keep it going continuously in the garden. In warm climates, it does not survive as a perennial beyond its range (it won’t tolerate tropical heat year-round), but in its proper zones it will return each year if conditions are suitable. Sometimes people confuse it with annual lobelia (such as the trailing Lobelia used in hanging baskets), but Great Blue Lobelia is a hardy perennial suited to garden beds.
Will Great Blue Lobelia come back every year?
If you live in roughly USDA Zone 4 through 9 (or even Zone 3 in protected spots), Great Blue Lobelia should come back each year as long as it’s planted in appropriate conditions. It’s winter-hardy in those regions and can survive freezing temperatures underground. Each spring, new shoots emerge from the base. However, an individual plant may only live a few years, so you might notice a particular clump weakening after 3-4 years. Fortunately, this plant often self-seeds near the original, so new young plants may pop up to replace any that die off, essentially keeping the patch going year after year. To ensure it returns, you can also collect seeds in fall and sow them, or divide healthy clumps to rejuvenate them. In summary, yes, it will come back annually within its hardiness range, but keep in mind the natural lifespan – gardeners often maintain a population of Great Blue Lobelia rather than relying on one long-lived plant indefinitely.
How does Great Blue Lobelia spread?
Great Blue Lobelia spreads primarily by seed. It doesn’t have running roots or stolons like some spreading plants; instead, after flowering, it produces many small seeds in capsules. These seeds can drop near the parent plant and germinate the next season, leading to clumps of new lobelia seedlings around the original plant. Over a few years, this results in a small colony or drift – effectively the plant “spreads” by populating the area with its offspring. The plant itself stays fairly clumped: one plant might get a bit wider as it produces multiple stems, but it won’t creep far on its own. You might also observe that sometimes the base of a mature plant can send up multiple rosettes or shoots that are essentially offsets; in that sense you could say it spreads a bit by clumping. But for covering ground or moving to new spots, seed dispersal is the mechanism. The seeds are tiny and can be carried a short distance by wind or water. Gardeners who prefer to contain its spread can deadhead the spent flowers to prevent seeding. Conversely, if you’d like it to naturalize and fill an area, allow the seeds to fall and perhaps lightly scratch them into the soil. Great Blue Lobelia is not invasive – while it can self-sow, it’s generally easy to manage or remove unwanted seedlings, and it tends to stay in moist areas where it’s planted.
Does Great Blue Lobelia attract hummingbirds and butterflies?
Yes. Great Blue Lobelia is known as an excellent pollinator plant that attracts hummingbirds, butterflies, and other pollinating insects. The bright blue, tubular flowers are particularly attractive to hummingbirds, which have long beaks well-suited to accessing the nectar deep in the flower. Gardeners often notice hummingbirds visiting lobelia blooms frequently (even though hummingbirds are famously drawn to red flowers like its cousin the cardinal flower, they also seek out these blue blossoms for nectar). Butterflies, especially larger species, will visit the flowers as well, sipping nectar from the tubular blooms. Certain species of bees, wasps, and even hoverflies can also be seen working the flowers – bumblebees are sometimes able to reach the nectar or will probe the blooms for pollen. The color blue is less visible to some insects (bees see it though), but the flower’s shape and nectar rewards ensure a variety of pollinators come by. In addition, after flowering, the seeds might attract small seed-eating birds (though the seeds are very fine, they are not a major bird food source like, say, coneflower seeds; however goldfinches and other small birds may nibble if seed heads are left). Overall, if you plant Great Blue Lobelia, you are very likely to enjoy more hummingbird visits in late summer, as well as butterflies adding life to your garden. It’s a great choice for a pollinator garden or anyone looking to support wildlife.
Is Great Blue Lobelia poisonous or safe for pets and people?
Great Blue Lobelia is considered poisonous if ingested by people or pets. All parts of the plant contain toxic alkaloids (like lobeline) that can cause gastrointestinal distress and other symptoms if consumed in significant quantity. This applies to dogs, cats, horses, and humans – so it’s not a plant to nibble on or use in home remedies without expert guidance. However, the good news is that the plant’s toxicity and taste usually deter animals from eating it. Most pets (and children) would find it very bitter and unpleasant. Simply touching or handling the plant is safe; it won’t irritate skin. The main caution is to prevent any curious grazing. If a pet did eat some, they might drool or vomit and should be monitored; contacting a vet would be wise if a large amount was eaten. Historically, Native Americans and herbalists used lobelia medicinally in controlled doses for various ailments, but those uses should not be attempted at home as the line between dose and poison is thin. In the garden, you can safely grow Great Blue Lobelia without fear as long as you don’t consume it. Its presence may even be beneficial in that it is deer and rabbit resistant due to being toxic. So, in summary: it’s poisonous when eaten (so keep pets and kids from snacking on it), but just growing it or touching it is fine.
Can Great Blue Lobelia grow in full sun?
Yes, Great Blue Lobelia can grow in full sun, but only if its water needs are met. In regions with mild summers or in northerly climates, full sun exposure (6 or more hours of direct sun per day) is usually fine and the plant will bloom heavily there – provided the soil stays consistently moist. In fact, in a sunny rain garden or beside a pond, Great Blue Lobelia can thrive in full sun because the water supply is ample. However, in hotter climates or during heat waves, full sun can cause stress if the soil begins to dry. Leaves may wilt or scorch under intense midday sun if moisture is insufficient. So while the plant is sun-tolerant, it’s not drought-tolerant. If you want to plant it in a sunny spot, be prepared to water often or choose a naturally damp location. Alternatively, many gardeners choose part sun or part shade locations for Great Blue Lobelia – somewhere it might get morning sun and afternoon shade, or light filtered sun all day. These conditions help keep it cooler and reduce evaporation from the soil. In summary, full sun is acceptable for Great Blue Lobelia in the right circumstances (especially in Zone 6 and cooler, or if soil is wet), but in warm regions partial shade might yield better results. Always monitor the soil moisture; sun plus dry soil will not work for this plant.
How do I grow Great Blue Lobelia from seed?
Growing Great Blue Lobelia from seed is quite feasible, though the seeds are tiny and have specific needs. Here’s a step-by-step overview: The seeds require a cold stratification period to break dormancy. You have two main approaches: sow outdoors or simulate winter indoors. For outdoor sowing, many gardeners simply sprinkle the fine seeds on the soil in late fall or winter (surface sow, do not cover them deeply as they need some light) in the area where you want them to grow. The winter cold and moist conditions naturally stratify the seeds, and they germinate in spring. Make sure the spot stays moist and that seeds won’t wash away – some people mix the seed with a bit of sand for more even distribution. If you prefer to start seeds in a controlled way, you can mix the seeds with a bit of damp sand or vermiculite in a plastic bag and refrigerate them for about 6 to 8 weeks (this mimics winter). After that period, sow them in seed-starting trays on the surface of the potting mix. Press them in lightly but don’t cover with thick soil. Keep the tray in a bright location (indoors under grow lights or outside in spring) and ensure it stays consistently moist (a clear humidity dome can help before germination). Germination might take a few weeks, so be patient. Once seedlings appear and develop a couple of true leaves, you can prick them out and pot them up, or carefully transplant them to the garden after frost. Seed-grown plants may or may not bloom the first year – often they will form a rosette the first year and then send up flowering spikes in their second growing season. Starting lobelia from seed is a rewarding way to get many plants inexpensively, but it does require that cold period and a moist environment. The good news is that established plants will do this on their own in the garden, dropping seed that sprouts next year. If you have existing plants, you can let nature do the work. If you’re starting from purchased seed, just remember: cold + moisture are key for germination, and don’t bury the seeds.
Should I deadhead Great Blue Lobelia after it blooms?
Deadheading (removing spent flower spikes) is not strictly required for the health of Great Blue Lobelia, but whether you do it or not depends on your goals. Once the plant has finished blooming (typically by early fall), you’ll have tall stems with seed pods. If you cut those stems down (deadhead), the plant will look tidier and you won’t have to see the drying seed pods. However, deadheading generally will not cause a rebloom on this plant – unlike some perennials, lobelia does not typically produce new flower spikes after the first flush is done (its bloom period is late in the season and the plant’s energy usually then goes into seed production). Occasionally, if spent spikes are removed very early and the growing season is long, you might get a few side shoots or a slight prolonging of the bloom period, but a full second bloom flush is unlikely. The main reasons to deadhead would be: 1) aesthetics, to keep the garden neat, 2) preventing self-seeding if you don’t want additional seedlings popping up, and 3) potentially to help the plant conserve energy (though many gardeners leave the seed stalks with no harm to the plant). On the flip side, leaving the seed heads on can allow the plant to reseed naturally, providing you with new baby plants next year; plus, some wildlife like small birds might investigate the dried seed pods for food. If you prefer a natural look or want it to multiply, you can skip deadheading. If you want controlled appearance or no volunteers, then deadhead. When deadheading, use clean pruners to cut the stalks off near the base or wherever foliage begins, once the flowers are finished. The plant’s rosette of green leaves may remain for a while into fall even after flowering is done, whether or not you remove the stalks.
What are good companion plants for Great Blue Lobelia?
Great Blue Lobelia pairs well with other moisture-loving garden plants, especially those that can share its preferred conditions of rich soil and full sun to part shade. One classic companion is its close relative, Cardinal flower (Lobelia cardinalis), which has bright red flowers and blooms around the same time – planting red cardinal flowers and blue lobelias together creates a stunning contrast and both attract hummingbirds. Other excellent companions include: swamp milkweed (Asclepias incarnata) which has pink flowers and similar moisture needs; Joe-Pye weed (Eutrochium purpureum or related species) with tall mauve-pink umbels that bloom in late summer; ironweed (Vernonia) with deep purple clusters; and black-eyed Susan (Rudbeckia) or orange coneflower (Rudbeckia fulgida) whose golden-yellow blooms look beautiful against blue lobelia and also enjoy moderately moist soil. For a shorter contrast, sedges or ornamental grasses that like wet soil (like Carex species) can provide nice textural pairing at the base of lobelias. In more shaded or woodland conditions, Great Blue Lobelia can be combined with ferns or plants like astilbe, which also prefer moisture and partial shade. Another idea is to plant it near Hydrangea shrubs (some hydrangeas have blue or pink blooms earlier in summer – by the time hydrangea flowers wane, the lobelia picks up the show). If your focus is natives, consider mixing it in a wildflower bed with blue flag iris (spring-blooming iris for wet areas), Cardinal flower (as mentioned), and perhaps marsh marigold or Jacob’s ladder for spring interest. In a formal border, you can use Great Blue Lobelia as a vertical accent among other perennials that appreciate some moisture like Monarda (bee balm) or Campanula. Just remember to place it where the soil won’t dry out – companions should be similarly moisture-inclined. Avoid planting it next to very drought-tolerant plants that need dry soil, as their needs conflict. Overall, think of other native wildflowers from wet meadows or stream banks, and you’ll find those often make great companions for lobelia, both visually and culturally.
Interesting tips
- Rain garden star: Great Blue Lobelia is an excellent choice for rain gardens and boggy spots. Use it in low areas of your landscape that collect water – it will happily soak up excess moisture and add beauty where many other plants would struggle. Its deep blue flowers also provide a nice contrast to the typically yellow and white blooms of other wetland-edge plants.
- Pair with late-season yellows: For a striking color combination, plant Great Blue Lobelia alongside yellow late bloomers. The blue-purple spikes look amazing next to plants like goldenrod or black-eyed Susans that flower in late summer. This blue-and-gold pairing is not only visually appealing but also creates a rich habitat for pollinators.
- Combine red and blue lobelias: Grow Great Blue Lobelia with its red-flowered cousin Cardinal flower in the same bed. Both have similar height and needs, but their contrasting colors (blue and scarlet) together create a wow factor in the garden. Hummingbirds will be especially thrilled, zipping back and forth between the red and blue blooms.
- Allow self-seeding for longevity: Because each lobelia plant is somewhat short-lived, a great tip is to let some of the flower stalks go to seed. The following spring, look for baby lobelia seedlings around the parent plant. You can transplant these to new spots or let them grow in place. This natural regeneration will keep your lobelia patch going strong for years without having to buy new plants.
- Mulch to prevent frost heave: In colder regions, protect your Great Blue Lobelia in winter by mulching around the base after the ground freezes. A couple of inches of mulch will stabilize soil temperatures and moisture. This prevents the freeze-thaw cycles from pushing the shallow-rooted plant upward. Come spring, simply remove the mulch so new shoots can sprout.
- Divide clumps periodically: Every 2-3 years, consider dividing established clumps in early spring. This will give the plant renewed vigor and also give you free new starts to plant elsewhere or share. Dividing helps because lobelia can get crowded and somewhat weaker in the center over time. Each division, with a portion of roots and shoots, will quickly re-establish itself when replanted in moist soil.
- Start seeds with winter sowing: An easy way to grow Great Blue Lobelia from seed is the “winter sowing” method. Sprinkle seeds in potting mix inside a ventilated clear container (like a milk jug) in winter and leave it outside. The natural chill and thaw of late winter will stratify the seeds, and they’ll germinate as the weather warms. This low-effort technique often yields lots of seedlings come spring, ready to be transplanted.
- Use in cut flower arrangements: Don’t hesitate to cut a few lobelia stems for indoor bouquets. Harvested at peak bloom, the spikes make an unusual and striking cut flower. They can last nearly a week in a vase if kept in clean water. Remove lower leaves, and combine the blue lobelia with white or yellow flowers and some greenery for a lovely arrangement. It’s a nice way to enjoy this native beauty up close.
- Historical fun fact: The name “siphilitica” is a nod to history – Native American tribes used the plant as part of a treatment for syphilis, which caught the attention of European settlers (hence the name). While the remedy didn’t prove truly effective, it’s an interesting example of ethnobotany. This history also underscores that despite any medicinal lore, the plant is potent and should be handled with respect (not consumed casually).
- Wildlife gardening: By planting Great Blue Lobelia, you’re not only adding color to your garden, but also supporting local wildlife. The nectar feeds pollinators late in the season when fewer flowers are in bloom. Plus, the fact that it’s a native wildflower means it fits well into the local ecosystem. Consider creating a mini wetland garden with lobelia, swamp iris, balloon flower, and others to attract butterflies and hummingbirds while beautifying a damp corner of your yard.