Trailing Lobelia Not Blooming? Heat & Light Are the Culprits

UK gardener's trailing blue lobelia in windowbox has lush foliage but few flowers by late June. Plants tripled in size, get some direct sun, watered generously each evening.

Why Lobelia Stops Blooming

• Heat: Above 23°C (73°F), flowering halts.
• Light: Needs 3–4 hours of direct sun. Too much shade OR all-day hot sun both stop blooms.
• Fertilization: If light/temp are okay, feed with balanced liquid fertilizer (10-10-10) after watering. Annuals are nitrogen-hungry.

Reality Check

Trailing lobelia is a "heartbreak plant" outside cool climates (like Alaska). In warm summers, it often becomes a green foliage plant. Enjoy the foliage, or replace with heat-tolerant alternatives like Scaevola or calibrachoa.