Lobelias are small plants, 3 to 10 inches tall, that are covered with the most vivid blue flowers imaginable from early summer until frost (Fig. 1). Lobelias have either very compact growth quite suitable to edgings or mass plantings, or long trailing stems, which will gently tumble over the edges of a container or raised bed, providing a bold splash of color wherever used. Cultivars are available with flowers of blue, violet, pink, white, or purple, often with a contrasting white or yellow eye.
Scientific name: Lobelia erinus
Pronunciation: loe-BEEL-lee-uh air-RYE-nuss
Common name(s): lobelia
Plant type: annual
USDA hardiness zones: all zones (Fig. 2)
Planting month for zone 7: May
Planting month for zone 8: Apr
Planting month for zone 9: Mar; Sep; Oct
Planting month for zone 10 and 11: Feb; Oct; Nov; Dec
Origin: not native to North America
Uses: container or above-ground planter; mass planting; border; attracts butterflies; cascading down a wall
Availability: grown in small quantities by a small number of nurseries
Height: 0 to 1 feet
Spread: 1 to 2 feet
Plant habit: spreading
Plant density: dense
Growth rate: fast
Leaf arrangement: alternate
Leaf type: simple
Leaf margin: crenate
Leaf shape: linear; obovate
Leaf venation: not applicable
Leaf type and persistence: not applicable
Leaf blade length: less than 2 inches
Leaf color: green
Fall color: not applicable
Fall characteristic: not applicable
Flower color: white; blue; pink; purple, violet
Flower characteristic: showy
Fruit shape: no fruit
Fruit length: no fruit
Fruit cover: no fruit
Fruit color: not applicable
Fruit characteristic: inconspicuous and not showy
Trunk and Branches
Trunk/bark/branches: not applicable
Current year stem/twig color: green
Current year stem/twig thickness: medium
Light requirement: plant grows in full sun
Soil tolerances: occasionally wet; clay; sand; acidic; loam
Drought tolerance: unknown
Soil salt tolerances: unknown
Plant spacing: 6 to 12 inches
Roots: not applicable
Winter interest: not applicable
Outstanding plant: not particularly outstanding
Invasive potential: not known to be invasive
Pest resistance: long-term health usually not affected by pests
Use and Management
Lobelia performs best in cool weather but is sensitive to frost. In warmer regions, lobelia should be planted in partial shade but can grow in full sun where summers are cool or hazy. Although lobelia will cease flowering when temperatures are too warm, they will quickly recover when temperatures drop in early fall. Provided with rich, fertile, well-drained soil and abundant moisture, lobelia is very easy to grow and quite a spectacular little plant.
Many cultivars are available: 'Blue Moon' has dark blue flowers; 'Cambridge Blue' has clear, soft blue flowers on compact, upright 4- to 6-inch plants; 'Crystal Palace', bronze-green leaves, dark blue flowers on compact plants; 'Paper Moon' has white flowers; 'Rosamunde', carmine red flowers with a white eye; 'White Lady'and 'Snowball', pure white flowers; 'Blue Cascade', 'Fountain' series, 'Hamburgia', and 'Sapphire' have trailing forms, suitable for hanging baskets or raised planters. 'Sapphire' has purple flowers with a white eye and is one of the best trailing lobelias.
Plants should be cut back after each flush of flowering to encourage new blossoms.
Propagation is by seed which germinates readily, with blooms appearing in four months.
Pests and Diseases
No pests are of major concern.
Damping-off, stem rot, root rot, if conditions are too damp.