Lobelia, Cardinal Flower (Lobelia)

Lobelias are probably best known for the annual summer bedding plant, indispensable for edging borders and for brightening up containers and hanging baskets. But there are also some gorgeous herbaceous perennial lobelias too.

Lobelia erinus is the annual, producing masses of flowers throughout the summer and well into autumn until the first severe frosts. There are two types: the upright, bushy varieties and those that have longer, trailing stems, making them perfect for hanging baskets and the edges of containers.

The best known perennial lobelia is Lobelia cardinalis, commonly called cardinal flower or bog sage, which produces tall spikes of scarlet red flowers in summer and autumn. An equally delightful species is, Lobelia tupa, which produces dark, bright red flowers on tall spikes at the same time.

How to grow lobelia

Cultivation

Bedding lobelia

Annual bedding lobelias will grow in both full sun or partial shade. A lightly shaded position, or one out of strong, direct sunshine, will ensure plants go on flowering profusely for a long time – especially during very hot summers.

They need a good, fertile, reliably moist soil, that doesn’t dry out in summer. So dig in lots of bulky organic matter, such as compost, to improve the moisture holding – especially on free-draining soils.

Perennial lobelia

Lobelia cardinalis can be grown in sun or, preferably, partial shade. It needs a good, fertile soil that remains moist during summer, and doesn’t dry out.

Lobelia tupa needs a sheltered position in full sun and a good, fertile, well-drained soil.

Lobelia varieties

  • Cambridge Blue Compact lobelia with clear sky blue flowers.
  • Crystal Palace Compact lobelia with deep blue flowers.
  • Colour Cascade Trailing lobelia with flowers in shades of blue, purple, red and white.
  • Mrs Clibran Improved Bushy, trailing lobelia with bright blue, white-eyed flowers.
  • Sapphire Compact lobelia with violet-blue flowers with a white eye.
  • White Cascade Trailing lobelia with ice white flowers.
  • Lobelia cardinalis Bees’ FlameBeetroot-red foliage. Bright scarlet flowers.
  • Lobelia cardinalis Black TrufflePurple-black foliage with purple-red highlights. Scarlet red flowers in summer.
  • Lobelia cardinalis Queen Victoria Deep maroon foliage. Bright scarlet flowers in summer and autumn.
  • Lobelia tupa Dark, bright red flowers in summer and autumn.

Sowing lobelia

Sow lobelia seeds from late winter until mid-spring in trays or pots of a good seed sowing compost. Place in a propagator at a temperature of 18-24C (65-75F) or seal it inside a polythene bag and keep somewhere warm.

When seedlings are large enough to handle, transplant into cell trays or small pots in clumps of up to 6 seedlings and grow on in cooler conditions. When well grown and all risk of frost has passed, harden off the young plants by acclimatising them to outdoor conditions for 7 to 10 days.

Lobelia tupa

Sow seeds in February or March, pots in pots or seed trays at a temperature of 21-25C (70-75F). Germination can take up to 1 month.

When seedlings are large enough to handle, transplant individually into 7.5-9cm (3-3.5in) pots. Gradually harden off the plants before planting out after all fear of frost.

Planting lobelia

Bedding plants should be planted out at the end of May or early June, after the fear of any frosts. If you have a greenhouse or other protected growing area, you can plant up containers and hanging baskets earlier for the plants to grow on and so flower earlier, before putting outside in early summer.

Plant out at a distance of 10-15cm (4-6in) apart.

Perennial lobelia plants can be planted at any time of year – providing the soil isn’t frozen solid or waterlogged – although they’ll establish quicker in autumn or early spring.

Dig over the planting area, incorporating lots of organic matter such as compost, leafmould or well-rotted manure. This is particularly important for Lobelia cardinalisas it needs a moist/wet soil. Dig a good sized hole big enough to easily accommodate the rootball.

Place the rootball in the planting hole and adjust the planting depth so that it is planted at the same depth as it was originally growing and the top of the rootball is level with the soil surface.

Mix in more organic matter with the excavated soil and fill in the planting hole. Water in well, apply a granular general feed over the soil around the plant and add a 5-7.5cm (2-3in) deep mulch of well-rotted garden compost or bark chippings around the root area.

Suggested planting locations and garden types

Flower borders and beds, patios, containers, city and courtyard gardens, cottage and informal gardens, bog gardens.

How to care for lobelia

Water plants whenever necessary to keep the soil or compost moist as this will prolong flowering.

Feed with a balanced liquid plant food every 2 weeks during spring and early summer and then switch to a high potash one every two weeks from then on.

Deadhead and cut back plants after flowering.

Water Lobelia cardinalis plants whenever necessary to keep the soil or compost moist or damp.

Feed with a general granular plant food each spring.

Cut back old flower stems after flowering and the old foliage in autumn. Lobelia tupa may need some winter protection. Apply a mulch of bark chips or straw in autumn to protect the crown.

Lobelia cardinalis is a short-lived perennial, so divide it every 2 years in spring to maintain its vigour.

Flowering season(s)

Summer, Autumn

Foliage season(s)

Spring, Summer, Autumn, Winter

Sunlight

Partial shade, Full sun

Soil type

Chalky, Clay, Loamy, Sandy

Soil pH

Neutral

Soil moisture

Moist but well-drained, Poorly drained

Ultimate height

Up to 1.5m (5ft) depending on variety

Ultimate spread

Up to 60cm (2ft) depending on variety

Time to ultimate height

4-6 months

Cutting Back Lobelia: When Should I Prune My Lobelia Plants

Lobelia flowers make a lovely addition to the garden but like many plants, pruning is an important part of keeping them looking their best. Keep reading to find out how and when to prune lobelia plants.

Should I Prune My Lobelia?

Yes. Cutting back lobelia plants improves their appearance and health. It also encourages the plant to produce more flowers over a longer period of time. The three types of pruning that benefit lobelia plants are removing spent flowers, pinching, and cutting back.

When to Trim Lobelia

The timing depends on the type of pruning. Pinching is an early spring task. Pinch back newly emerging stems when they are about six inches long. Pinch newly planted lobelia when they recover from transplanting. Give the plant a light trim any time of year. Do the major pruning or cutting back after the plants stop blooming.

How to Prune Lobelia Flowers

Pinching plants means taking off the tips and top two leaves of tender, young growth. It encourages bushy growth and better flowering. The best tool for the job is a thumbnail. Squeeze the tip of the stem between your thumbnail and index finger to make a clean break.

Give the plant a light trim with a pair of scissors when it needs a bit of tidying. This includes trimming to remove spent blossoms. For spiky types, wait until the entire spike has faded before clipping out the stems.

Cut back the plant by half or more at the end of its bloom period. Trimming back lobelia plants keeps them from looking messy, and it may encourage another flush of blooms.

Pruning Edging and Trailing Lobelia

These two little plants grow only about 6 inches tall. They survive winters in U.S. Department of Agriculture plant hardiness zones 10 and 11, but they are usually grown as spring annuals because they fade in the summer heat.

Edging and trailing lobelia follow a schedule similar to pansies and linaria, and most growers remove them in early summer when they no longer look their best. If you decide to leave them in the garden, cut them back by one-half to two-thirds to encourage fall blooms. Edging and trailing lobelias are classified as self-cleaning, which means you don’t have to deadhead them.

Annual Lobelia Plant: How To Grow Lobelia

The lobelia plant (Lobelia spp.) is an attractive annual herb with many varieties. Some of these even include biennial species. Lobelia is an easy-to-grow, carefree plant that enjoys cool weather. This summertime bloomer will continue to produce flowers on up through the first frost. Growing lobelia is an asset to the garden.

Types & Uses of Lobelia Plants

While there are numerous varieties of lobelia plants, only a few are commonly seen in the home garden—L. inflata (Indian tobacco), L. cardinalis (Cardinal flower), and L. siphilitica. Interesting enough, the name of Indian tobacco derived from the fact that Native Americans once smoked lobelia plant to treat asthma. Also known as pukeweed, doctors once prescribed the plant to induce vomiting.

Although most varieties are compact, growing only 3 to 5 inches (7.5-12.5 cm.) tall, others will

grow up to 3 feet (1 m.). Colors are also variable, with white, pink, red and blue species available. However, violet-blue is probably one of the most commonly seen. These plants make great additions in borders, along creeks or ponds, as ground covers, or in containers—especially hanging baskets.

Growing Lobelia Plant

Annual lobelia will grow nearly anywhere. Lobelia seeds can be sown directly in the garden or indoors for later transplanting. These plants typically require an area with full sun but will tolerate partial shade. They also prefer moist, rich soil. Start indoors about 10 to 12 weeks prior to the last frost in your region. Spread the tiny seeds just on top of the soil and water thoroughly. Place them in a warm, well-lit area.

The seedlings should pop up within a week or two, at which time you can begin thinning them out. After all danger of frost is gone and the plants are at least 2 to 3 inches (5-7.5 cm.) tall, transplant them to the garden—spacing about 4 to 6 inches (10-15 cm.) apart.

Care of Lobelia Plants

Once established, the lobelia plant requires little maintenance. During hot, dry periods, care of lobelia requires that the plant should receive frequent watering, however, especially those in containers. A general-purpose liquid fertilizer can be given once a month or every four to six weeks, if desired.

Lobelia should delight your garden with beautiful blooms about mid-summer, continuing on up to the first frost. Although not necessary, you can deadhead lobelia plants to maintain a neat appearance.

Lobelia cardinalis

  • Attributes: Genus: Lobelia Species: cardinalis Family: Campanulaceae Life Cycle: Perennial Recommended Propagation Strategy: Leaf Cutting Root Cutting Seed Stem Cutting Country Or Region Of Origin: Eastern United States Fire Risk Rating: medium flammability Wildlife Value: Its flowers are attractive to hummingbirds and butterflies. Play Value: Wildlife Food Source Dimensions: Height: 4 ft. 0 in. – 5 ft. 0 in. Width: 1 ft. 0 in. – 2 ft. 0 in.
  • Whole Plant Traits: Plant Type: Herbaceous Perennial Native Plant Perennial Poisonous Water Plant Wildflower Leaf Characteristics: Deciduous Habit/Form: Erect Maintenance: Low
  • Cultural Conditions: Light: Deep shade (Less than 2 hours to no direct sunlight) Full sun (6 or more hours of direct sunlight a day) Partial Shade (Direct sunlight only part of the day, 2-6 hours) Soil Texture: High Organic Matter Soil Drainage: Moist Occasionally Wet NC Region: Coastal Mountains Piedmont Usda Plant Hardiness Zone: 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b
  • Fruit: Display/Harvest Time: Fall Fruit Description: Displays from August to November
  • Flowers: Flower Color: Pink Red/Burgundy White Flower Inflorescence: Raceme Flower Value To Gardener: Showy Flower Bloom Time: Fall Summer Flower Shape: Tubular Flower Size: 1-3 inches Flower Description: The Cardinal flower features erect, terminal spikes (racemes) of large, cardinal red flowers. Each flower is about 1.5 in. long. A tube of stamens projects upward through a cleft in the corol. The tubular flowers are 2-lipped, with the three lobes of the lower lip appearing more prominent than the two lobes of the upper lip. The flowers begin opening at the bottom of a terminal flower spike and continue to the top. Although not common, white and rose-colored varieties also exist. Blooms from July to October.

  • Leaves: Leaf Characteristics: Deciduous Leaf Color: Green Leaf Arrangement: Alternate Leaf Shape: Lanceolate Leaf Margin: Dentate Hairs Present: No Leaf Description: The Cardinal flower has finely-toothed, lance-shaped, dark green leaves (to 4″ long). The leaves form on branched, alternate-leaved stalks rising typically to a height of 2-3′ (infrequently to 4′)
  • Stem: Stem Is Aromatic: No
  • Landscape: Landscape Location: Naturalized Area Riparian Woodland Landscape Theme: Butterfly Garden Native Garden Pollinator Garden Rain Garden Water Garden Attracts: Butterflies Hummingbirds Pollinators Resistance To Challenges: Rabbits Wet Soil Problems: Poisonous to Humans Problem for Cats Problem for Dogs Problem for Horses
  • Poisonous to Humans: Poison Severity: Medium Poison Symptoms: TOXIC ONLY IF LARGE QUANTITIES EATEN. Nausea, vomiting, diarrhea, salivation, exhaustion and weakness, dilation of pupils, convulsions, and coma. Poison Toxic Principle: Alkaloids lobelamine, lobeline, and others, plus a volatile oil Causes Contact Dermatitis: No Poison Part: Flowers Fruits Leaves Roots Sap/Juice Seeds Stems

Plant of the Week: Cardinal Flower

The University of Arkansas System Division of Agriculture does not promote, support or recommend plants featured in “Plant of the Week.” Please consult your local Extension office for plants suitable for your region.

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Cardinal Flower
Latin: Lobielia cardinalis

Cardinal flower is the brightest of our red flowered wildflowers. (UofA Division of Agriculture photo by Gerald Klingaman)

Having just returned from a fieldtrip with a number of botanists, I now have more appreciation for this special breed of scientists. What I found most amazing, and frankly puzzling, was their collective excitement at finding some obscure, tiny and often ugly flower most gardeners wouldn’t give a second look. But even scientists can have their heads turned by a pretty face. They all seem to like Cardinal flower (Lobelia cardinalis).

Cardinal flower is a native perennial growing 3- to 4-feet tall and producing intense scarlet blooms in late summer and fall at the end of unbranched stems. Over winter, plants die back to an evergreen clump that sees the plant through the winter. The leaves are smooth (glabrous) and often purple or maroon tinged and to 4 inches long. Lobelia belongs to the bluebell family.

Individual blooms of cardinal flower are tubular with three broad prominently displayed petals and two more slender, upturned petals that remind me of the ears on Batman’s mask. Protruding from each flower are the sexual parts of the flower that are strategically placed to distribute pollen when visited by ruby throated hummingbirds as they make their rounds.

In a survey of botanists in the middle of the last century cardinal flower was listed as their favorite flower. Like most surveys, this one seems to have a fatal flaw. It required that botanists choose from the plants that grew locally, so obviously any plant with a broad distribution had a leg up. Cardinal flower had the advantage of a showy presence and a wide range from eastern Canada to California and south through Mexico to northern Columbia. Though it has a wide range it favors wet, wild places so it doesn’t suffer the stigma of being too common in any locale.

Lobelia was introduced to Europe by the English plant collector John Tradescant in 1626.

The genus was named for the Flemish botanist Mathias de l’Obel (1538 – 1616) who wrote under the Latinized form of his name Lobelius. The common name came not from our native bird, but from the scarlet vestments worn by high-ranking officials of the Catholic Church.

Of late, attempts have been made to domesticate the cardinal flower by crossing it with several other species in an attempt to extend the color range and increase the flower size. The first of these three way European hybrids appeared in the early 1990s as the “Fan Series” using L. siphilitica (blue) and L. fulgens (red). A hybrid with Mexican lobelia (L. fulgens) called “Queen Victoria” has maroon foliage and is less winter hardy.

Cardinal flowers have few specific requirements as to soil type other than one critical need; moisture. In nature it is a bog or streamside plant, so don’t expect this to survive in the typical dry border where it is forced to compete with other garden perennials. It will grow in full sun or partial shade but is perhaps at its best in sites with full sun until mid-afternoon when some natural shade is provided by a structure or a tree canopy. Queen Victoria can be grown directly in a water garden. Some plant cardinal flowers at the base of a downspout so they are watered with every shower.

If well-sited cardinal flowers will form individual clumps the first year and then form a small colony as slender rhizomes spread it about. It will also reseed in moist sites. The species is hardy from zones 3 through 9 but the hybrids are only hardy through zone 7. Individual plants are usually short lived but in good locations will reseed freely.

By: Gerald Klingaman, retired
Extension Horticulturist – Ornamentals
Extension News – September 25, 2009

The University of Arkansas Division of Agriculture does not maintain lists of retail outlets where these plants can be purchased. Please check your local nursery or other retail outlets to ask about the availability of these plants for your growing area.

How to Cut Back Lobelia

Jupiterimages/Photos.com/Getty Images

Lobelia, or Lobelia erinus, is an annual plant that produces delicate blossoms in shades of blue, white, pink or purple. Commonly grown as a groundcover or hanging plant, lobelia requires well-drained soil and full sunlight to partial shade. Cutting back a lobelia plant will increase the blooming season and increase the number of new blossoms.

Pinch back the tips of the young lobelia plants when you purchase them from the nursery. Without this initial pinching, the stems can grow long and make the plant look leggy and unkempt. Use your fingertips or a pair of sharp pruning shears to remove just the outside tip of each stem.

Water the lobelia to keep the soil slightly moist at the depths of the roots. Allow the surface of the soil to dry out slightly between watering sessions. Although lobelia can withstand a range of soil conditions, this plant grows best in slightly damp soil, especially during the intense heat of summer.

Examine your lobelias throughout the growing season. Keep the plant shape attractive and uniform by trimming back any long stems that grow beyond the average length of the main foliage. Look for any dried-out or broken stems. Minimize the risk of disease and enhance the appearance of a lobelia plant by trimming off the damaged growth as soon as it appears. Dip your pruning shears in a disinfectant solution that contains nine parts water to one part chlorine bleach, to avoid spreading bacteria or fungus spores between plants.

Cut back the entire plant after the initial wave of blossoms begins to fade. Using your pruning shears, cleanly remove the top 1/2 of the entire plant. This heavy pruning early in the summer will encourage the start of another flowering session. Water lobelia plants deeply after heavy pruning to reduce plant shock.

Remove the cut vegetation from the soil surrounding the lobelia plant. Leaving the dead material in the area increases the risk of both pests and disease conditions. Watch for the second flowering session to start within three to four weeks. Continue to check the lobelia plant regularly and trim back any dead, dried or leggy stems.

(FreeImages.com/Lennart Jireland)

Interested in growing a flower that looks dainty and elegant, yet is an easy-to-maintain repeat bloomer? Try growing lobelia in your summer garden. These carefree flowering plants remain covered with eye-catching blooms throughout the summer months, and even into the fall. Flower colors are brilliant, coming in stunning violet-blue, as well as yellow, white, red and pink.

Featuring a charming cascading habit, lobelia makes an excellent choice for window boxes, raised beds, hanging baskets and containers. It also does well as a ground cover. Even better, lobelia tends to be deer resistant, and the flowers attract butterflies and hummingbirds.

For the best of luck growing lobelia, keep these cultivation tips in mind.

Plant in full sun to partial shade. Locate lobelia in an area that gets five or more hours of sunlight each day. The plant will bloom in partial shade. The best part-sun situation for lobelia is morning sun and afternoon shade.

(FreeImages.com/Simon Coomber)

Ensure good drainage. Like many plants, lobelia doesn’t do well in soggy soil. Prior to planting, check that the planting area drains well. If water drains slowly, amend the area with homemade or bagged compost and recheck the drainage. Avoid drainage issues by planting in containers with high-quality, organic potting soil.

Water regularly. Lobelia requires consistent soil moisture for prolific blooms. Water the plants regularly in the absence of rainfall, so that the soil is moist but not soggy. To help keep the soil surrounding lobelia consistently moist, mulch with a 2-inch layer of ground bark or leaf mold.

(FreeImages.com/Jean-Pierre Cremers)

Prune occasionally. To have the most blooms, it’s necessary to pinch or prune lobelia back to keep it bushy, which will lead to continual flowering. Once flowers fade, prune them off and new buds will appear.

Fertilize monthly. Feed lobelia on a regular basis with an organic fertilizer designed for flowering plants. Apply monthly from spring through early fall.

Julie Bawden-Davis is a garden writer and master gardener, who since 1985 has written for publications such as The American Gardener, Organic Gardening, Wildflower, Better Homes and Gardens and The Los Angeles Times. She is the author of seven books, including Reader’s Digest Flower Gardening, Fairy Gardening, The Strawberry Story, and Indoor Gardening the Organic Way, and is the founder of HealthyHouseplants.com.

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