How to Grow Lobelia

Posted by Jessica Mcnamara on

Lobelia is a stunning flowering plant known for its vibrant blue, purple, pink, and white blooms. Perfect for adding a splash of colour to your garden, lobelia is relatively easy to grow and care for. This guide will walk you through everything you need to know about growing lobelia, from planting to maintenance.

Choosing the Right Lobelia Variety

Annual vs. Perennial Lobelia

There are two main types of lobelia: annual and perennial. Annual lobelia (Lobelia erinus) is most commonly grown in gardens and containers, blooming profusely throughout the summer. Perennial lobelia (Lobelia cardinalis and Lobelia siphilitica) returns year after year, often producing taller and more substantial flowers.

Selecting a Variety

Popular varieties of lobelia include:

  • Lobelia erinus: Ideal for borders and hanging baskets.
  • Lobelia cardinalis: Known for its striking red flowers.
  • Lobelia siphilitica: Features tall spikes of blue flowers, perfect for wet areas.

Planting Lobelia

When to Plant

Lobelia seeds should be sown indoors 8-10 weeks before the last frost date. If you prefer transplanting seedlings, wait until all danger of frost has passed.

Soil Preparation

Lobelia thrives in rich, well-draining soil. Before planting, amend the soil with organic matter such as compost to improve fertility and drainage.

Sowing Seeds

  • Fill a seed tray with a light, seed-starting mix.
  • Sprinkle the tiny lobelia seeds evenly across the surface.
  • Lightly press the seeds into the soil without covering them, as they need light to germinate.
  • Water gently to moisten the soil without washing away the seeds.
  • Place the tray in a warm, bright location, ideally around 18-24°C (65-75°F).

Transplanting Seedlings

Once the seedlings have developed two to three sets of true leaves, they are ready to be transplanted outdoors. Space the plants about 10-15 cm (4-6 inches) apart to allow for adequate air circulation.

Caring for Lobelia


Lobelia prefers consistently moist soil. Water regularly, especially during dry spells, but avoid waterlogging the soil.


Feed lobelia with a balanced, water-soluble fertiliser every two weeks during the growing season to encourage continuous blooming.

Pruning and Deadheading

Regularly deadhead spent flowers to prolong the blooming period. For perennial varieties, cut back the plants after flowering to promote new growth.

Common Problems and Solutions


Lobelia is relatively pest-free but can occasionally attract aphids and slugs. Use organic pest control methods such as neem oil or diatomaceous earth to manage infestations.


Lobelia can be susceptible to fungal diseases like powdery mildew and root rot. Ensure good air circulation, avoid overhead watering, and plant in well-draining soil to prevent these issues.

Overwintering Perennial Lobelia

In colder climates, perennial lobelia may need protection over the winter. Mulch around the base of the plants with straw or leaves to insulate the roots. In extremely cold areas, consider lifting the plants and storing them in a cool, frost-free place until spring.

Growing lobelia can be a rewarding addition to your garden, offering vibrant colours and lush foliage. With the right care and attention, lobelia will flourish and bring beauty to your outdoor space. Happy gardening from all of us at Marshall's Garden!

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