Great lobelia
Lobelia siphilitica · Campanulaceae
The gardener's calendar
Ideal time to plant great lobelia: set it out when the soil is neither frozen nor waterlogged, and water generously as it establishes.
ID card
- Scientific name
- Lobelia siphilitica
- Family
- Campanulaceae
- Type
- Perennial herbaceous plant
- Flowering
- July to September
- Flower color
- Intense cobalt blue
- Adult size
- 60 to 120 cm in height
- Hardiness
- Very hardy (-20°C and below)
- Origin
- North America
Care
Regular and generous watering
Giant lobelia appreciates constantly moist soil without being waterlogged. Water regularly, especially during the growing season and dry summers. This plant is water-hungry and doesn't tolerate prolonged droughts. Check soil moisture before each watering and adjust frequency according to your climate.
Partial sun exposure
Install giant lobelia in a sunny to partially shaded location (at least 4 to 6 hours of direct sunlight). It tolerates partial shade well and will flower generously in these conditions. In very hot climates, protection from the intense afternoon sun is beneficial.
Rich and well-drained soil
Prepare fertile substrate, rich in organic matter and slightly moist. Amend the soil with compost or well-decomposed potting soil. A neutral to slightly acidic pH is ideal. Improve drainage if the soil is too compact by adding sand or perlite.
Moderate fertilization during growth
Apply a balanced fertilizer once a month from April to July to support growth and flowering. Reduce fertilization after flowering. Excess nitrogen promotes foliage at the expense of flowers.
Deadheading and winter cutting back
Regularly remove faded flowers to extend flowering. In autumn, after the first frosts or in spring, cut the plant back near ground level. This regular cutting back regenerates the clump and promotes abundant flowering the following year.
Monitoring for pests and diseases
Giant lobelia is generally little affected by diseases. Watch for powdery mildew in cases of stagnant, humid air. Excess soil moisture can promote root rot. Ensure good drainage and adequate air circulation to prevent these problems.
Did you know?
Giant lobelia gets its name 'siphilitica' due to a historical legend: in the 17th century, it was said to have been used by Native American peoples to treat certain afflictions, which intrigued the first European botanists. Although this historical name persists, the plant is now chiefly appreciated for its spectacular cobalt blue flowers that brighten shaded gardens and wet areas.
Where to buy it
Plant in spring or early autumn, avoiding spells of intense heat. Pick a plant with healthy foliage and roots that are not exposed. Best time: March, April, May, September.
Add this plant to my garden →Plants from the same family
- Peach-leaved bellflowerCampanula persicifolia
- Clustered bellflowerCampanula glomerata
- Trailing bellflowerCampanula poscharskyana
- Dalmatian bellflowerCampanula portenschlagiana
- PānakenakeLobelia angulata
- Carpathian bellflowerCampanula carpatica
Tips generated and checked by Viridia — adapt them to your local climate.