Edging lobelia

Edging lobelia: how do you recognise it?

Habit

Low and finely branched: compact forms of 10–15 cm, trailing forms with stems up to 30 cm long.

Leaves

Small, narrow to oval and slightly toothed; fresh green, bronze-green in some varieties.

Flower

Two-lipped and barely 1–2 cm, with three broad lobes below and two narrow ones above.

Colour

Dark blue, sky blue, purple, pink or white, often with a white eye.

Roots

Fine and shallow: the plant dries out quickly, especially in pots.

Flowering: May–September · Sowing: February–March · Plants: May · Pruning: July

Why grow it?

• One of the few bedding plants with truly deep blue flowers.
• Flowers from May to September, with a second flush after a trim in July.
• Compact forms make a neat edge; trailing forms tumble gracefully from containers and baskets.
• Happy in sun and in light partial shade.
• Neatly fills the gaps between larger plants in containers.

Edging lobelia: where does it grow best?

• Sun or light partial shade; in full sun the soil must stay moist.
• Fertile, humus-rich soil or potting compost: sand, loam or clay, acid to neutral.
• Evenly moist, without standing water.
• Plant 10–15 cm apart for edging; closer in hanging baskets.

Light

Sun and partial shade

Soil type

Sand, loam or clay

Acidity

Acid or neutral

Moisture

Normal

Size

0.15 m tall, 0.2 m wide

Hardiness

Frost tender: plant out after the last frost (mid-May)

Goes well with

• Zonal geranium: The blue flowers make a fresh edge beneath red or pink.
• Petunia: Large trumpet flowers above it in containers and hanging baskets.
• Fuchsia: In light partial shade, with lobelia as a low edge.
• Sweet alyssum: White and blue as a classic low edging.
• Million bells: Together in a hanging basket they spill down like a colourful waterfall.

Edging lobelia: when and how to plant it?

Plant in May.

1. Plant out in the second half of May, once there is no more risk of night frost.
2. Harden the plants off for a week first: outside by day, inside at night.
3. Loosen the soil and mix in a little compost, or fill your container with fresh potting compost.
4. Plant each clump of seedlings whole, at the same depth as in the pot, 10–15 cm apart.
5. Water in at once and keep the soil well moist for the first few weeks.

Care

Watering

Never let the soil dry out, or flowering stops. Check containers and baskets daily in summer.

Feeding

From June to late August a liquid flowering-plant feed every two weeks, especially in pots.

Deadheading

Not needed; a trim in July does more good.

Heat

In a heatwave flowering sometimes stops. Move pots into partial shade for a while and water in the morning.

Tip: Water hanging baskets of lobelia every day in summer: drying out completely just once can halt flowering for weeks.

Edging lobelia: when to prune it?

Pruning months: July.

When: In July, after the first flush of flowers, when the plant looks bare or untidy.

How:

• Cut the whole plant back by a third with scissors.
• Then keep it well watered and give a flowering-plant feed.
• After a few weeks it regrows and flowers again into September.

Caution: Do not trim during a heatwave or when the plant has dried out: water first and wait for cooler weather.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow indoors in February–March at 18–20 °C. Sprinkle the dust-fine seed in small pinches on moist seed compost and do not cover it. Prick out each clump whole.

Cuttings

Trailing varieties in summer: tip cuttings of 5 cm in moist cutting compost, under plastic in good light but out of full sun.

Edging lobelia: how does it get through the winter?

Hardy to 0 °C: protect in harsh winters.

• Not hardy: it dies in frost.
• Treat it as an annual and sow or buy new plants each year.
• Clear the plants after the first frost.

Diseases and pests

• Damping off: A fungus makes young seedlings collapse. Do not sow too thickly, use clean pots and fresh seed compost, and give plenty of fresh air.
• Flowering stops: Caused by drought or heat. Water, trim back and feed; in cooler weather it flowers again.
• Red spider mite: Fine yellow speckles on the leaves in hot, dry weather. Keep the soil moist and spray the leaves with water.
• Root rot: In a pot without a drainage hole the roots rot. Always make sure there is a hole in the bottom.

Through the year

• February: Sow indoors in pinches, leaving the seed uncovered.
• March: Keep sowing. Prick out clumps of seedlings.
• April: Grow on in a light, cool place. Start hardening off in late April.
• May: After mid-May, plant out 10–15 cm apart.
• June: Full bloom. Water and feed.
• July: After the first flush, cut back by a third.
• August: Second flush. Keep the soil moist.
• September: Last flowers. Clear at the first frost.

Edible and useful

Not edible. All parts of lobelia are poisonous: they contain lobeline and related alkaloids, which act like nicotine. Swallowing any causes nausea, vomiting, drooling and stomach ache, and in larger amounts dizziness, sweating, a fast heartbeat and breathing problems. A related species was once used as a herb for asthma and to stop smoking: never make teas or preparations from your garden lobelia. Keep children, dogs, cats and grazing animals away from the plant, and wear gloves when cutting back, as the milky sap can irritate the skin. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Did you know?

• The genus is named after Matthias de l’Obel (1538–1616), a Flemish botanist and physician from Lille. He was physician to William of Orange and later botanist to King James I of England.
• In its homeland, southern Africa, it grows as an annual or a short-lived perennial.
• The seed is as fine as dust: that is why you sow it in pinches and plant each clump out whole.