How to grow lobelia
Overview
Lobelia erinus is a compact, herbaceous annual grown for its profuse small flowers in blue, purple, pink, or white. It thrives in cool, mild seasons and is ideal for filling gaps in borders, containers, and hanging baskets.
Varieties
- Crystal Palace — Compact, dark blue flowers with bronze-green foliage, ideal for edging.
- Riviera Series — Early-flowering mix in blue, white, and pink, good for pots.
- Regatta Series — Trailing habit for hanging baskets, with blue, rose, and white blooms.
Soil Preparation
Lobelia prefers well-drained, moist soil with a pH of 6.0–7.0. Enrich with compost or well-rotted manure before planting. In heavy clay, add coarse sand or raise beds to improve drainage.
Growing Guide
Sow seed on the surface of fine seed compost from late winter to early spring in temperate zones, or in autumn in subtropical and Mediterranean areas. Do not cover seed; press lightly and keep moist. Space seedlings 10–15 cm apart in part shade with morning sun. Pinch out tips at 5 cm to encourage bushiness. Avoid letting the soil dry out completely.
Sowing
Sow seed on the surface of moist seed mix; do not cover as light aids germination. Germinates in 10–14 days at 18–21°C. Transplant when 4–6 true leaves appear. Direct sowing is possible but less reliable; start in punnets for best results.
Care
Feed every two weeks with a balanced liquid fertiliser (e.g., 10-10-10) during active growth. Deadhead spent flowers regularly to prolong blooming and prevent early seeding. Trim back leggy stems to keep the plant compact and bushy.
Companion Planting
Plant lobelia with petunias, alyssum, and verbena for a continuous colour display. Avoid placing near tall, spreading plants that will shade or crowd it out.
Common Pests & Risks
Aphids cluster on new growth and can be hosed off or treated with insecticidal soap. Slugs and snails chew leaves and stems; use iron-based pellets or beer traps. Downy mildew may appear in humid, crowded conditions; improve air circulation and avoid overhead watering.
Troubleshooting
Yellow leaves: overwatering or poor drainage; reduce watering and check roots. Brown leaf edges: dry air or underwatering; increase humidity or water more frequently. Leggy growth: insufficient light; move to brighter spot or pinch back. Few flowers: too much nitrogen or heat stress; switch to bloom-booster fertiliser and provide shade. Sudden collapse: root rot from soggy soil; ensure drainage and avoid overwatering.