<em>Lobelia</em>, lobelia: sowing, planting, cultivation, care
Contents
Lobelia in a nutshell
- Lobelias or lobelias are perennials or annuals with long, abundant flowering in blue, white, red, pink or purple
- Their flowers in delicate clusters open continuously from May to October
- Annuals such as Lobelia erinus are kings of hanging baskets
- Easy to grow and maintain, lobelias prefer sunny or semi-shaded positions and light, rich, moist, well-drained soil
- Erect, spreading or trailing, lobelia lends itself to all sorts of uses in beds, borders, hanging baskets, window boxes or near water features
A word from our expert
Known for its cascades of small annual blue or white flowers in window boxes or hanging baskets, the Lobelia is also a tall perennial with vivid colours.
While trailing lobelias erinus with blue flowers (Lobelia pendula ‘Monsoon’) or white ‘White Cascade‘ is the star of hanging baskets from June to first frosts, perennial Lobelia such as red Lobelia cardinalis makes a striking display in borders, in beds where soil stays cool in summer and even on banks of water features.
Generous and hardy (-7 to -20°C depending on species), short-lived perennial lobelia thrives in non-scorching sun and in fresh to moist, fertile and well-drained soil.
Most tender lobelias make lovely border plants or potted plants to overwinter sheltered from frost in colder regions.
Shrubby, groundcover or trailing, lobelia lends itself to endless possibilities to brighten every corner of garden or terrace with its vivid colours.
Blue Lobelia (‘Hot Blue’), white Lobelia or red Lobelia, choose our lobelias from our collections of plug plants or our lobelia seeds for a flowering summer! Essential in summer arrangements, hanging baskets and window boxes!
Description and botany
Botanical data
- Latin name Lobelia
- Family Campanulaceae
- Common name Lobelia, lobelia, cardinal flower
- Flowering from May to autumn
- Height 0.10 to 1 m
- Exposure Sun, partial shade
- Soil type All, well-drained
- Hardiness -7°C to -25°C depending on variety
Genus Lobelia of family Campanulaceae includes 370 annual, perennial or shrubby species. Also called cardinal flower, Lobelia grows in tropical and temperate regions worldwide, mainly in Americas.
Within this large genus, there are large perennial lobelias (Lobelia cardinalis, Lobelia siphilitica and hybrid lobelias such as Lobelia x speciosa and Lobelia x gerardii) with generous flowering in upright clusters, similar to spikes; plus more tender lobelias grown as annuals in our climates such as king of hanging baskets, Lobelia erinus, with tiny flowers of an astonishing blue, available in several dozen varieties (Lobelia ‘Hot Blue’, ‘Royal Blue’, ‘Water Blue’…).
Lobelias display very variable silhouettes in habit spreading, bushy, groundcover, trailing to erect depending on species and cultivars. Annual lobelias, such as Lobelia erinus that perish at first frosts, are mat-forming or trailing and do not exceed 0.10 m in height, while perennial species form erect clumps of 0.50 to 1 m in height.
Numerous thin or sturdy ramified stems according to species quickly form a bushy clump. Although growth can be rapid, perennial lobelia is in fact a short-lived perennial that needs dividing to be kept for many years in garden.
Lobelia cardinalis – botanical illustration.
In spring, from a rhizomatous clump forming basal rosettes emerges narrow, delicate foliage that makes a fine setting for flowering. All lobelias bear simple, alternate leaves along the stem, linear, ovate, oblong to lanceolate and dentate on margins.
Bright green, medium green to dark green, sometimes tinged with red or bronze, often glossy, sometimes slightly downy, leaves measure 1 to 15 cm and are often sessile. Lobelia x speciosa stands out by very attractive purplish to chocolate-tinged foliage borne on stems of same hue. All hybrid lobelias are deciduous, their foliage disappearing entirely in winter; some, such as Lobelia laxiflora, retain evergreen leaves.
This delicate growth gives way to a shimmering mass of flowers from June, sometimes as early as April depending on climate, until first frosts. Annual lobelia flowers continuously from spring to autumn, while perennial lobelias generally bloom in mid-summer between July and September.
Each leafy stem ends in spikes of terminal or solitary clusters, light and variably long (up to 45 cm), composed of tubular two-lipped flowers with a very particular structure. Corollas measure 0.5 to 5 cm in diameter and are divided into five lobes with two very narrow upper petals and three wider lower petals, rather spread in a fan evoking butterfly wings or snapdragon flowers. Calyx tubes are generally swollen.
In Lobelia laxiflora, also called “loose-flowered lobelia”, flowers are longer and narrower, semi-pendulous and end in a saw-tooth pattern with two yellow lips.
Whether perennial or annual, lobelia is available in many colourways depending on variety: tiny ultramarine-blue flowers with a tiny white eye of Lobelia erinus (‘Hot Blue’, ‘Royal Blue’, ‘Water Blue’…) to brilliant red of Lobelia cardinalis, purple flowers of Lobelia gerardii ‘Vedrariensis’ and Lobelia siphilitica, vivid pink of Lobelia speciosa ‘Tania’, through to bright white of ‘White Cascade’ or Lobelia siphilitica ‘Alba’.
Lobelia hardiness is highly variable according to species and growing conditions. Hardiest perennial lobelias (Lobelia cardinalis, Lobelia siphilitica) can withstand negative temperatures down to -25°C; most tender lobelias are grown as annuals or as conservatory plants in a large pot that is moved away from severe frosts in cool climates.
All lobelias appreciate well-drained, light, fresh and humus-rich soil and prefer well-sunny situations but not scorching sun.
Lobelia is indispensable in all summer compositions. Annual lobelia brightens window boxes and hanging baskets — a staple for container growing — and also suits rockeries or borders. Large perennial lobelias are perfect at back of border but also in front of a bed where they bring height and lightness. Some, such as L. cardinalis and L. siphilitica, appreciate moist soils of woodland understorey or pond edges.
Several flower colours: Lobelia ‘Monet Moment’, Lobelia fulgens ‘Queen Victoria’, Lobelia ‘Russian Princess’, Lobelia siphilitica ‘Alba’, Lobelia sessilifolia.
Lobelia inflata was traditionally used in America to relieve respiratory troubles. With effects similar to nicotine, this plant was used as a substitute to help people quit smoking.
Main species and varieties
Le lobelia belongs to a large family in which annual lobelia varieties coexist with other perennials with mat-forming, trailing and even shrubby habits. The annual lobelia forms a more-or-less cascading flowering cushion and does not exceed 0.20 m in height, whereas perennial species form bushy clumps that can reach 1 m in height.
There are more than 350 lobelia species and among the best known are lobelia erinus, a small annual “queen of hanging baskets”, most often flowering a brilliant blue, sometimes white, available in several dozen varieties (Lobelia ‘Hot Blue’, ‘Royal Blue’, ‘Water Blue’, ‘Pendula’…), lobelia cardinalis, an 80 cm tall perennial that bears bright red flowers, Lobelia siphilitica, a very hardy perennial (at least down to -15°C). Many hybrids exist as well, such as lobelia speciosa, a fine perennial hybrid with red, pink, blue or purple flowers, and Lobelia x gerardii, a perennial with purple flowering. Occasionally encountered is Lobelia laxiflora or loose-flowered lobelia, a somewhat tender perennial with very exotic charm.
Lobelia fulgens Queen Victoria
- Flowering time August to November
- Height at maturity 80 cm
Lobelia gerardii Vedrariensis
- Flowering time September, October
- Height at maturity 70 cm
Lobelia siphilitica Alba
- Flowering time August to November
- Height at maturity 90 cm
Lobelia speciosa Russian Princess
- Flowering time September to November
- Height at maturity 80 cm
Lobelia speciosa Tania
- Flowering time September to November
- Height at maturity 70 cm
Lobelia speciosa Monet Moment
- Flowering time June to September
- Height at maturity 80 cm
Lobelia erinus Hot Water Blue - Trailing Lobelia
- Flowering time July to November
- Height at maturity 30 cm
Lobelia erinus Purple Star - Trailing Lobelia
- Flowering time July to November
- Height at maturity 30 cm
Lobelia erinus pendula Hot Bavaria - Trailing Lobelia
- Flowering time July to November
- Height at maturity 30 cm
Lobelia Anabel Blue
- Flowering time July to November
- Height at maturity 30 cm
Lobelia erinus Deep Blue Star - Trailing Lobelia
- Flowering time July to November
- Height at maturity 30 cm
Cascade Collection of Lobelias
- Flowering time July to November
- Height at maturity 25 cm
Lobelia erinus Monsoon - Trailing Lobelia seeds
- Flowering time July to September
- Height at maturity 15 cm
Discover other Lobelia
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Planting and sowing
Where to plant lobelia
Lobelia hardiness varies according to species and growing conditions. Hardy perennial lobelias can be planted outdoors, tolerating temperatures from -7°C to -25°C.
Annual lobelias, which are more tender, are grown in a large pot that can be kept frost-free in severe climates. In regions with heavy frosts, it is still advisable to mulch the base of perennial lobelias to protect the stump in winter. It grows across much of France but is trickier to cultivate in hot, dry or cold, wet regions. It thrives in sunny but not scorching positions or in semi-shade. The annual lobelia, “king of hanging baskets”, with its trailing habit, is ideal in hanging baskets, summer window boxes and also in borders or rockeries, where it forms a pretty
All lobelias prefer a well-drained, light, cool soil rich in humus that stays cool, even moist in summer but not waterlogged. Winter damp is fatal: they need a well-drained soil in winter.
Some species such as Lobelia siphilitica even tolerate short periods of root submersion; it is ideal in water gardens, waterside borders and in woodlands.
The perennial lobelia lightens back of borders, bringing verticality and lightness with generous flowering in upright clusters. Varieties that appreciate cool, even moist soils in summer (L. cardinalis and L. siphilitica) can be planted on banks of a pond.
When to sow and plant lobelia
Sow annual lobelia from March under cover.
Plant perennial Lobelia in open ground from March to June, after spring frosts in cold climates, or in September–October in warm climates.
How to plant and sow lobelia
On receipt, pot on and keep our young lobelia plug plants under cover (conservatory, greenhouse, cold frame…) at a temperature above 14°C for a few weeks before planting out once frost risk has passed.
Variable in habit and colours, they can be planted in pots of course, but also in borders or even in a green wall.
In open ground
Plant lobelia plants spaced 30 cm apart. Prefer group planting for striking effects in a border. In heavy soil, add compost or potting compost to lighten substrate and ensure good drainage.
- Dig a hole two to three times wider than the rootball
- Add a little river sand or gravel to the bottom of the hole
- Plant without burying the collar of the plant
- Backfill with the excavated soil mixed with compost or potting compost
- Firm down with hand or foot
- Mulch and water generously and frequently to encourage rapid establishment
Planting annual lobelia in hanging baskets or pots
Plant several plants in the same container to create an attractive group effect, spacing plants 20 to 30 cm apart. Keep the growing medium consistently cool and moist.
- Plant in a mix of potting compost and garden compost
- Spread a good layer of drainage (gravel or clay pebbles) at the bottom of the pot for good drainage
- Mulch and water regularly
Lobelia ‘Hot White’ brightens part-shaded corners beautifully.
Sowing lobelia
Flowering appears in the first year; find lobelia seeds in our nursery.
Under cover:
- Sow under cover between 18 and 24°C, preferably in buckets rather than seed trays, as lobelia seedlings are quite fragile
- Mix seeds with a little sand to sow into a special seed compost
- Cover seeds barely with a very fine film of compost
- Keep slightly moist
- Firm down with a board
- Place buckets in sun
- Seeds will germinate in 14 to 21 days
- When seedlings are large enough, plant into window boxes or pots in a rich, cool growing medium
- Put them outside for a few hours a day if nights are still cool to acclimatise gradually
In open ground:
Sow directly into well-prepared soil enriched with compost or leaf mould, after last frosts, usually around May.
- Cover with a thin layer of growing medium
- Firm down
- Water and keep soil moist until germination
- Pull out surplus plants to leave 20 to 30 cm between plants
Care and maintenance
Lobelia requires little care provided soil is sufficiently fertile, perfectly drained and fairly cool in summer.
It needs regular watering, even more so in periods of severe drought, to flower abundantly: soil must remain cool. Mulch in May to conserve moisture at the base (gravel, flax chippings…) and reduce watering.
Lobelia is a heavy feeder; to flower abundantly it needs feeding. Apply well‑rotted compost or manure at the base of perennial Lobelia plants each year in early spring.
For more generous flowering, every 15 days from May to August, give a liquid feed to Lobelias grown in pots or in hanging baskets.
Remove faded flowers as they go to encourage new inflorescences. Don’t hesitate to prune after the first flowering to encourage a second flowering.
In spring, cut back growth severely to encourage the plant to ramify. Cut off faded flower stems of perennial Lobelias.
In autumn, put pots of the most tender Lobelias into storage as you would orangery plants in harsh climates — in a cool, bright, frost‑free room. During winter, reduce watering.
To keep plants for many years, divide the largest clumps in spring every two or three years.
Possible diseases and pests
Generally hardy, Lobelia mainly dislikes wet soil in winter. In heavy, poorly drained soil, it can lead to collar rot.
In spring, protect young foliage from being eaten by slugs and snails, use fern manure to fight their attacks and follow our advice to combat and prevent the damage they cause.
Multiplication
If Lobelia can be propagated by sowing, we recommend clump division of perennials in spring. Carry out on well-established plants aged 2 to 3 years.
- With a spade, gently separate the small rosettes formed around the base of the plant
- Replant these divisions immediately in the garden in well-worked, free-draining soil
Associate
With its form alternately narrow and airy, or bushy and trailing, Lobelia is precious in borders, as isolated specimen, in hanging baskets, at water’s edge or to create compact masses in border beds and add volume. Vertical stems with erect spikes of large perennial lobelias emphasise the curve of a composition of a light cloud of small flowers. Indispensable for composing fabulous romantic or blazing summer scenes.
A planting idea: rose ‘Rosy Cushion’, Lobelia ‘Monet Moment’, Echinacea purpurea ‘Virgin’, Pennisetum orientale, Gillenia trifoliata.
In borders, pair with lavateras, cleomes and nicotianas. In beds with phlox, late astilbes, anemones, impatiens.
Groundcover varieties form plump, floriferous cushions that will gently dress base of shrub rose or clematis, insert between slightly taller summer plants or other annuals, or fill hanging baskets throughout summer.
Red-flowered varieties go wonderfully with grasses such as Pennisetum, Stipa, Carex, and with small blue flowers of tall verbenas, blue thistles and asters.
Lobelias’ astonishing blue flowers or their glowing colours mix nicely with cool colour schemes, silver, bluish or glaucous foliage such as Argyanthemum, dusty millers, Helichrysum, small fescues, Hostas and Artemisia lactiflora. It forms a beautiful contrast with yellow foliage of a Carex. Appreciate with bidens, hardy geraniums, French marigolds and veronicas.
Lobelia fulgens and Lobelia cardinalis will be magnificent by water features in damp settings with Physostegia virginiana bearing white or pink flowers.
Also create pretty flowering containers by mixing annual lobelias, petunias and Calibrachoas.
An example combination for a lovely summer container: Lobelia ‘Magadi Electric Blue’ (similar to variety ‘Hot Water Blue’), Oxalis deppei and Begonia tuberosa ‘Breezy Yellow’.
Useful resources
- Create beautiful, original and long-flowering summer or spring planters — it’s possible and easier than it seems with our annual plug plants
- How to plant window boxes and hanging baskets with annual plug plants?
- How to create a beautiful perennial border with our hardy lobelias?
- Discover our 7 planting combination ideas to create beautiful summer planters
- Subscribe!
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