*Lobelia*, *lobélie* : sowing, planting, cultivation, maintenance

Description and Botany

The genus Lobelia from the family Campanulaceae, comprises 370 annual, perennial or shrubby species. Also known as Cardinal of the marsh, Lobelia grows in tropical and temperate regions worldwide, but mainly in America.

Within this large family, we distinguish the large perennial lobelias (Lobelia cardinalis, Lobelia siphilitica and hybrid lobelias such as Lobelia x speciosa and Lobelia x gerardii) with their generous flowering in upright clusters, resembling spikes, from more tender lobelias cultivated in our climates as annuals like the king of hanging baskets, Lobelia erinus with its small flowers of an incredible blue, which comes in several dozen varieties (Lobelia ‘Hot Blue’, ‘Royal Blue’, ‘Water Blue’…).

Lobelias take on very variable silhouettes in their spreading, bushy, tapestry, trailing or upright habits depending on the species and cultivars. Annual lobelias, such as Lobelia erinus that die off at the first frosts, are tapestry or trailing species not exceeding 0.10 m in height, while perennial species form erect clumps of 0.50 to 1 m in height.

The numerous slender or sturdy branched stems, depending on the species, quickly form a bushy clump. While growth is rapid, the perennial lobelia is actually a short-lived perennial that needs to be divided to be perpetuated for many years in the garden.

Lobelia cardinalis – botanical illustration.

In spring, from a rhizomatous clump forming basal rosettes, emerges a narrow and light foliage that provides a beautiful setting for the flowering. All lobelias bear simple, alternate leaves along the stem, linear, ovate, oblong to lanceolate and dentate on the margins.

Bright green, medium green to dark green, sometimes tinged with red or bronze, often glossy, sometimes slightly downy, they are 1 to 15 cm long and often lack a petiole. Lobelia x speciosa stands out with its beautiful purple foliage with chocolate reflections, borne by stems of the same hue. All hybrid lobelias are deciduous, their foliage completely disappears in winter, while some like Lobelia laxiflora retain their evergreen leaves.

This delicate vegetation disappears under a shimmering mass of flowers from June, sometimes as early as April depending on the climate, at the first frosts. The annual lobelia blooms continuously from spring to autumn, while perennial lobelias generally flourish in the heart of summer between July and September.

Each leafy stem ends in spikes of terminal or solitary clusters, light and varying lengths (up to 45 cm long), formed of tubular flowers with two lips, featuring a very particular architecture. Their corollas measure 0.5 to 5 cm in diameter and are cut into five lobes with two very fine petals at the top and three broader lower petals, rather spread out like a fan, somewhat resembling butterfly wings or the flowers of snapdragons. The calyx tubes are generally swollen.

In Lobelia laxiflora, also known as “Lobelia with loose flowers”, the flowers are longer and narrower semi-pendulous and end in serrated tips with two yellow lips.

Whether perennial or annual, lobelia comes in many colours depending on the varieties: small flowers of an ultramarine blue dotted with a tiny white heart from Lobelia erinus (‘Hot Blue’, ‘Royal Blue’, ‘Water Blue’…) to the bright red of Lobelia cardinalis, to the purple flowers of Lobelia gerardii ‘Vedrariensis’ and Lobelia syphilitica, the bright pink of Lobelia speciosa ‘Tania’, through to the brilliant white of ‘White Cascade‘ or Lobelia siphilitica ‘Alba’.

Lobelia has a very variable hardiness depending on the species and growing conditions. The hardiest perennial lobelias (Lobelia cardinalis, Lobelia siphilitica) can withstand negative temperatures down to -25°C, while the more tender lobelias are grown as annuals or as greenhouse plants, in a large pot that is sheltered from severe frosts in cool climates.

All lobelias appreciate well-drained, light, cool soil rich in humus and enjoy well-sunny situations but not scorching rays.

Lobelia is essential in all summer compositions. The annual lobelia brightens up window boxes and hanging baskets – it is a must for container gardening – but also for rockeries or borders. The large perennial lobelias are perfect for the back of borders but also in the foreground of a flower bed, bringing height and lightness. Some like L. cardinalis and L. siphilitica appreciate the moist soils of a woodland or the banks of a pond.

Several flower colours: Lobelia ‘Monet Moment’, Lobelia fulgens ‘Queen Victoria’, Lobelia ‘Russian Princess’, Lobelia siphilitica ‘Alba’, Lobelia sessilifolia.

Lobelia inflata has been traditionally used in America to relieve respiratory tract disorders. With effects similar to those of nicotine, this plant was used as a substitute to help quit smoking.

Main species and varieties

The Most Popular Perennial Lobelias

Our Favourite Perennial Lobelias

The Most Popular Annual Lobelias

Our Favourite Annual Lobelias

Lobelia fulgens Queen Victoria

A colourful lobelia that forms a magnificent upright tuft of purple leaves, with superb spikes of blood-red flowers. Its late flowering accompanies all the colours of autumn.

• Flowering time August to November
• Height at maturity 80 cm

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Lobelia gerardii Vedrariensis

A beautiful perennial lobelia one metre tall with purple flowering from July to September. It is one of the easiest to grow.

• Flowering time September, October
• Height at maturity 70 cm

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Lobelia siphilitica Alba

A charming perennial lobelia that is rarely found in gardens. It thrives in heavy, ordinary, cool to moist soils and tolerates short periods of root submersion. It is ideal for water gardens, in border beds by ponds, and in woodlands.

• Flowering time August to November
• Height at maturity 90 cm

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Lobelia speciosa Russian Princess

This colourful hybrid lobelia deserves to be used more in wet gardens or by water features. It provides a striking contrast with light foliage.

• Flowering time September to November
• Height at maturity 80 cm

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Lobelia speciosa Tania

A variety with very colourful bright pink flowers that will enliven your beds from this summer.

• Flowering time September to November
• Height at maturity 70 cm

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Lobelia speciosa Monet Moment

A very floriferous perennial lobelia that should be overwintered in a frost-free place.

• Flowering time June to September
• Height at maturity 80 cm

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Lobelia erinus Hot Water Blue - Trailing Lobelia

This excellent annual is a recent introduction, superb in summer compositions.

• Flowering time July to November
• Height at maturity 30 cm

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Lobelia erinus Purple Star - Trailing Lobelia

This lobelia looks from afar like an enchanting purple cloud in hanging baskets and window boxes!

• Flowering time July to November
• Height at maturity 30 cm

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Lobelia erinus pendula Hot Bavaria - Trailing Lobelia

This round annual with small bicoloured flowers is a recent introduction, floriferous and heat-resistant.

• Flowering time July to November
• Height at maturity 30 cm

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Lobelia Anabel Blue

A new lobelia from the Hot series that withstands heat much better than traditional varieties. Its rather upright ball shape creates an enchanting and lasting display, filling sunny planters.

• Flowering time July to November
• Height at maturity 30 cm

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Lobelia erinus Deep Blue Star - Trailing Lobelia

Nothing stops the flowering and growth of this excellent early and floriferous variety, which blooms until the first frosts.

• Flowering time July to November
• Height at maturity 30 cm

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Cascade Collection of Lobelias

An assortment of 5 trailing lobelias in a mix of white, bright blue, dark blue, and purple that bloom continuously throughout the summer.

• Flowering time July to November
• Height at maturity 25 cm

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Lobelia erinus Monsoon - Trailing Lobelia seeds

A small flowering annual that fills window boxes and hanging baskets. Its cushion-like shape adds volume to compositions.

• Flowering time July to September
• Height at maturity 15 cm

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Planting and sowing

Where to Plant Lobelia

The hardiness of Lobelia varies depending on the species and growing conditions. Hardy perennial lobelias can be planted in the ground, withstanding negative temperatures from -7°C to -25°C.

The annual lobelias, which are more sensitive, should be grown in a large pot that can be sheltered from frost in harsh climates. In regions where severe frosts are common, it is still advisable to mulch the base of perennial lobelias to protect the stump in winter. It grows well throughout France, but its cultivation will be more challenging in hot, dry regions or cold, damp areas. It thrives in sunny situations but not scorching or semi-shaded conditions. The annual lobelia, the “king of hanging baskets”, with its trailing habit, is ideal for hanging baskets, summer planters, and also in borders or rockeries where it forms a lovely plump, floriferous cushion.

All Lobelias prefer well-drained, light, fresh soil rich in humus that remains cool, even moist in summer but not waterlogged. Winter moisture is fatal to it: it needs well-drained soil in winter.

Some species, such as Lobelia siphilitica, can even tolerate short periods of root submersion; it is ideal for water gardens, pond edges, and in woodlands.

The perennial lobelia lightens the base of borders, bringing verticality and lightness with their generous flowering in upright clusters. Varieties that prefer cool, even moist soils in summer (L. cardinalis and L. siphilitica) can be planted on the banks of a water feature.

When to Sow and Plant Lobelia

Sow annual lobelia from March under cover.

Plant perennial Lobelia in the ground from March to June, after spring frosts in cold climates, in September-October in warm climates.

How to Plant and Sow Lobelia

Upon receipt, transplant and store our young lobelia plants in plug plants under cover (veranda, greenhouse, cold frame…) at a temperature above 14°C for a few weeks before being placed outside as soon as frosts are no longer a concern.

Variable in their habit and colours, they can be planted in pots, but also in borders or even in a green wall.

In the Ground

Plant lobelia plants spaced 30 cm apart. Prefer a group planting for beautiful effects in a border. In heavy soil, add compost or potting soil to lighten the substrate and ensure good drainage.

• Dig a hole 2 to 3 times wider than the root ball
• Add a bit of 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 soil
• Firm down with your hand or foot
• Mulch and water generously and frequently to encourage quick recovery

Planting Annual Lobelia in Hanging Baskets or Pots

Plant several young plants in the same container to create a beautiful group effect, spacing the plants 20 to 30 cm apart. Keep the substrate consistently moist.

• Plant in a mixture of potting soil and compost.
• Spread a good layer of drainage (gravel or clay balls) at the bottom of the pot for good drainage
• Mulch and water regularly

Lobelia ‘Hot White’ beautifully brightens shady corners.

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 pots rather than in trays, as young lobelia seedlings are quite fragile.
• Mix the seeds with a bit of sand to sow them in a special seed compost
• Barely cover the seeds with a very fine layer of substrate
• Keep slightly moist
• Firm down with a board
• Place the pots in the sun
• The seeds will germinate in 14 to 21 days
• When the seedlings are large enough, transplant them into planters or pots in rich, fresh substrate
• Take them outside for a few hours each day if nights are still cool to acclimatise them gradually

In the Ground:

Sow directly in well-prepared soil enriched with compost or leaf mould, after the last frosts, usually in May.

• Cover with a thin layer of substrate
• Firm down
• Water and keep the soil moist until germination
• Thin out excess plants to leave 20 to 30 cm between each

Maintenance and care

The Lobelia requires little care as long as the soil remains sufficiently rich, perfectly drained, and cool enough in summer.

It needs regular watering, especially during intense drought, to bloom abundantly: the soil must stay moist. Mulch in May to retain moisture at the base with gravel, pale flax, etc., and limit watering.

Lobelia is a greedy plant; to bloom profusely, it needs to be fed. Apply well-rotted compost or manure at the base of perennial lobelia plants each year at the beginning of spring.

For a more generous flowering, every 15 days from May to August, provide liquid fertiliser to lobelias grown in pots or hanging baskets.

Remove faded flowers as they appear to encourage new inflorescences. Don’t hesitate to prune after the first flowering to promote a second bloom.

In spring, cut back the vegetation severely to encourage the plant to ramify. Cut off the faded flower spikes of perennial lobelias.

In autumn, store the pots of the most tender lobelias like citrus plants in harsh climates in a cool, bright, frost-free location. During the winter period, reduce watering.

To keep the plants for many years, divide the largest clumps in spring every two or three years.

Diseases and potential pests

Generally resilient, Lobelia is primarily sensitive to wet soil in winter. In heavy, poorly drained soil, it can lead to collar rot.

In spring, protect the young foliage from the appetite of slugs and snails, use fern manure to combat their attacks, and follow our tips to fight and prevent their damage.

Multiplication

If Lobelia is propagated by sowing, we recommend clump division of perennials in spring. Proceed with plants that are 2 to 3 years old and well-established.

• Using a spade, gently separate the small rosettes formed around the edge of the clump
• Immediately replant these divisions in the garden in well-tilled and well-draining soil

Associate

With its silhouette that can be narrow and light, or bushy and trailing, Lobelia is invaluable in borders, as a specimen plant, in hanging baskets, by the water’s edge, or to create compact masses in flower beds and add volume. The vertical spikes with erect spikes of large perennial lobelias enhance the curvature of a composition featuring a light cloud of small flowers. It is essential for creating fabulous romantic or fiery summer scenes.

An idea for combination: rose ‘Rosy Cushion’, Lobelia ‘Monet Moment’, Echinacea purpurea ‘Virgin’, Pennisetum orientale, Gillenia trifoliata.

In borders, it can be paired with lavateras, cleomes, and tobaccos. In flower beds, it works well with phlox, late astilbes, anemones, and impatiens.

The trailing varieties form plump, floriferous cushions that will delicately dress the base of a bush rose or a clematis, fit in between slightly taller summer flowers or other annual flowers, or fill hanging baskets throughout the summer.

The red-flowered varieties will pair beautifully with grasses such as Pennisetum, Stipa, Carex, the small blue flowers of tall verbena, blue thistles, and asters.

The flowers of an unusual blue or the brilliant colours of lobelias blend nicely with cool colours, silver, blue, or glaucous foliage such as Argyanthemum, cinerarias, helichrysum, small fescues, Hostas, and Artemisia lactiflora. It creates a beautiful contrast with the yellow foliage of a Carex. It is appreciated alongside bidens, hardy geraniums, marigolds, and veronicas.

Lobelia fulgens and cardinalis will look magnificent by water features in humid settings alongside Physostegia virginiana with white or pink flowers.

You can also create lovely flowering pots by mixing annual lobelias, petunias, and Calibrachoas.

An example of a combination for a beautiful summer pot: Lobelia ‘Magadi Electric Blue’ (similar to the variety ‘Hot Water Blue’), Oxalis deppei, and Begonia tuberosa ‘Breezy Yellow’.