Great blue lobelia

Great blue lobelia: how do you recognise it?

Habit

Upright, clump-forming perennial about 80 cm tall and 30 cm wide, with unbranched, leafy stems.

Leaves

Lance-shaped to oblong, 5–15 cm long, green, with a slightly toothed edge; a rosette at the base, then scattered along the stem.

Flower

Blue (sometimes white) two-lipped tubular flowers of 2–3 cm in dense, leafy spikes, from August to October.

Sap

Milky sap in stems and leaves, which is poisonous and can irritate the skin.

Roots

Shallow, fibrous root system that needs plenty of moisture; forms ever thicker clumps.

Flowering: August–October · Plants: April–May and September · Pruning: March

Why grow it?

• Blue flowers from August to October, when few other perennials are still in bloom.
• Fully hardy (to about −30 °C) and much easier than the red species.
• Suits moist soil where many perennials fail: pond edge, stream bank or damp border.
• The flowers are visited by bumblebees and bees in late summer.
• Seeds itself in suitable spots, giving you free new plants.

Great blue lobelia: where does it grow best?

• Sun to part shade; in sun it needs more water.
• Humus-rich loam, clay or peaty soil that stays moist, acid to neutral.
• Normal to wet: the soil must never dry out; it also tolerates temporarily wet feet in summer.
• Suits a pond edge, stream bank, damp border and wild garden.
• Allow 30–40 cm between plants.

Light

Sun and partial shade

Soil type

Loam, clay or peat

Acidity

Acid or neutral

Moisture

Normal or wet

Size

0.8 m tall, 0.3 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Joe Pye weed: Tall and pink, flowers at the same time in the same moist soil.
• Coneflower: Yellow that contrasts beautifully with the blue.
• Michaelmas daisy: Flowers at the same time in blue and purple.
• Purple moor grass: Fine grass that frames the flower spikes lightly.

Great blue lobelia: when and how to plant it?

Plant in April–May and September.

1. Plant in April–May or in September, when the soil is neither frozen nor bone dry.
2. Mix a generous amount of compost or leaf mould into the soil.
3. Dig a hole as deep as the pot and twice as wide.
4. Set the plant at the same depth as in its pot and space plants 30–40 cm apart.
5. Water well straight away and keep the soil moist for the first weeks.
6. Spread a 5 cm layer of leaf mould or bark around the base.

Care

Watering

Keep constantly moist, also during dry spells and especially in the first year.

Feeding

Compost or an organic fertiliser in spring. More is not needed.

Mulching

A layer of leaf mould in spring keeps the soil cool and moist.

Spent flowers

Leave the spikes if you want it to self-seed; cut them off for a tidy border.

Support

In an open or windy spot, tie in the tall stems or let them grow through other plants.

Tip: Hardier than the red lobelia and less fussy. Give it moist soil; it seeds itself freely if you leave the stems standing.

Great blue lobelia: when to prune it?

Pruning months: March.

When: In March cut away the old stems; in autumn only if you want a tidy border.

How:

• In March, cut the old stems down to just above the ground, without damaging the new rosettes.
• Leave the stems standing in autumn if you want the plant to self-seed; they also give the border winter structure.
• Cut faded spikes back to just above a side shoot if you do not want seedlings.

Caution: Wear gloves: the milky sap is poisonous and can irritate the skin.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

Every three to four years in April or September: lift the clump, divide it into pieces with roots and a rosette and replant straight away.

Sowing

The seed is very fine, needs light and germinates best after a cold spell: sow on the surface in autumn or early spring and do not cover it.

Moving seedlings

Seedlings that have self-sown in the garden can be moved in spring while they are still small.

Great blue lobelia: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, down to about −30 °C: no protection is needed in Belgian winters.
• Leave the leaf rosettes in place over winter; they protect the plant.
• In a pot: stand the pot in a sheltered corner and make sure it never dries out completely.

Diseases and pests

• Slugs: Young rosettes and shoots are eaten in spring. Collect them in the evening and protect young plants.
• Drying out: Limp leaves and brown edges in dry weather. Water and mulch.
• Too much self-seeding: Seedlings can overrun neighbours. Weed them out in spring or cut the spikes before the seed ripens.
• Aphids: Sometimes on young shoots. A jet of water is usually enough.

Through the year

• March: Cut back old stems. Apply compost.
• April: Plant or divide. Watch for slugs.
• May: Plant. Mulch.
• July: Water in dry weather. Support tall stems.
• August: Flowering begins.
• September: Flowering. Plant or divide.
• October: Last flowers. Leave the spikes for seed or cut them off.

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.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• In the wild the plant grows in wet meadows and along streams in the east of North America.
• The tubular flowers with their broad lower lip are pollinated mainly by bumblebees, which are sturdy enough to land on them.
• It flowers into October and so still gives late bumblebees and bees some nectar.