How to Grow Lobelia: A Comprehensive Guide for Gardeners

how to grow lobelia

Lobelia, with its vibrant blooms and versatile nature, is a favourite among gardeners. Whether you’re drawn to the cascading charm of the annual varieties or the upright style of lobelia perennial species, we’ll guide you through how to grow Lobelia in your garden and enjoy its blooms.

Understanding Lobelia

Lobelia plants come in both annual and perennial varieties. The perennial lobelia, often featuring spikes of blue, violet, or red flowers, adds a striking vertical element to gardens. On the other hand, annual lobelia varieties are known for their ongoing flowering and trailing habit – making them ideal for hanging baskets and borders.

Choosing the Right Variety

When selecting lobelia, consider the specific needs of your garden. Perennial lobelia species, like Lobelia cardinalis or Lobelia siphilitica, are excellent for adding height and colour to perennial borders. For a cascading effect in containers or hanging baskets, the annual Lobelia erinus varieties are a perfect choice.

Starting with Lobelia Seedlings

Growing lobelia from seed can be a rewarding experience. Start lobelia seedlings indoors about 10-12 weeks before the last frost date. Lobelia seeds require light to germinate, so simply press them onto the surface of a moist seed-starting mix and keep them under bright, indirect light. Maintain a consistent temperature of around 70-75°F (21-24°C) for optimal germination.

Planting Lobelia

Once the danger of frost has passed and your lobelia seedlings have developed a few true leaves, they’re ready to be transplanted outdoors. Choose a location that receives full sun to partial shade. Lobelia plants thrive in well-draining soil with moderate moisture. When planting perennial lobelia, space them about 12-18 inches apart to allow for mature growth.

Watering and Feeding

Regular watering is crucial, especially for newly planted lobelia seedlings. Keep the soil consistently moist but not soggy. Too much water can lead to root rot, particularly in perennial lobelia. A balanced, water-soluble fertilizer applied every 4-6 weeks can promote healthy growth and abundant flowering.

Pruning and Maintenance

Deadheading, or removing spent flowers, can encourage more blooms and extend the flowering period. For perennial lobelia, cut back the foliage in late fall or early spring to promote fresh growth. Annual lobelia varieties may benefit from a mid-season trim to rejuvenate the plants and encourage further flowering.

Overwintering Perennial Lobelia

In colder climates, perennial lobelia may require some winter protection. Mulching around the base of the plants can help insulate the roots. In regions with severe winters, consider lifting and storing the tubers in a cool, dry place until spring.

Pests and Diseases

Lobelia plants are generally hardy but can occasionally suffer from aphids or slugs. Regular inspections and prompt treatment with appropriate methods can keep these pests at bay. Good air circulation and proper watering practices can prevent most fungal diseases.


Growing lobelia, be it the charming annual varieties or the majestic perennial lobelia, can add colour and interest to any garden. By starting with healthy lobelia seedlings, providing the right growing conditions, and performing regular maintenance, you can enjoy the delightful blooms of lobelia throughout the growing season. Whether in beds, borders, or containers, lobelia plants are a fantastic choice for gardeners looking to add a touch of elegance and vibrancy to their outdoor spaces.

If the Lobelia isn’t quite the plant you’re looking for, then why not read about the Anchusa which is similar but with slightly different flowers.

Lobelia Frequently Asked Questions

How to Keep Lobelia Blooming All Summer

To ensure your lobelia plants provide a continuous display of blooms throughout the summer, follow these key tips:

  • Regular Watering: Lobelia plants thrive with consistent moisture. Ensure the soil remains evenly moist but not soggy. During hot, dry periods, increase the frequency of watering to prevent the soil from drying out completely.
  • Adequate Sunlight: While lobelia can tolerate partial shade, they bloom best in full sun to partial shade. Ensure your plants receive at least 4-6 hours of sunlight daily for optimal flowering.
  • Deadheading: Regularly remove spent flowers (deadheading) to encourage lobelia plants to produce more blooms. This process prevents the plants from putting energy into seed production and instead focuses on creating new flowers.
  • Fertilization: Feed your lobelia plants with a balanced, water-soluble fertilizer every 4-6 weeks. This will provide the necessary nutrients for sustained growth and blooming. Avoid over-fertilizing, as this can lead to more foliage growth at the expense of flowers.
  • Pruning: If your lobelia plants start to look leggy or sparse in mid-summer, don’t hesitate to give them a light trim. Cutting back the plants by about half can rejuvenate them and encourage a new flush of blooms.
  • Proper Planting: Ensure lobelia plants have enough space for air circulation to prevent disease. Overcrowded plants can become stressed and less likely to bloom profusely.
  • Pest and Disease Control: Keep an eye out for signs of pests or diseases. Healthy plants are more likely to produce a continuous display of flowers. Treat any infestations or infections promptly with appropriate methods.

By following these care tips, your lobelia plants should keep blooming beautifully all summer long, adding vibrant colour and life to your garden.

When to Plant Lobelia in the UK

The best time to plant lobelia in the UK largely depends on the type of lobelia you are growing and whether you are starting from seed or using young plants.

  • Starting from Seed Indoors: If you’re growing lobelia from seed, begin sowing indoors in late winter to early spring, around February to April. Lobelia seeds need a warm environment to germinate, so starting them indoors allows you to control the temperature and protect them from late frosts.
  • Transplanting Seedlings Outdoors: Lobelia seedlings should be moved outdoors after the risk of frost has passed. This is typically from mid to late May in most parts of the UK. Before transplanting, it’s important to acclimatize the seedlings to outdoor conditions by gradually increasing their exposure to outside temperatures over a week or two, a process known as hardening off.
  • Planting Young Plants or Plug Plants: If you have purchased young lobelia plants or plug plants, these can also be planted out after the last frost, usually from mid-May onwards. Ensure they are well-acclimatized to outdoor conditions before planting.
  • Direct Sowing: In warmer parts of the UK, you can sow lobelia seeds directly into the ground or containers in late spring, once the soil has warmed up and there’s no risk of frost. This is usually around late May to early June.

Remember, lobelia thrives in well-draining soil and a sunny to partly shaded spot. By planting at the right time and providing the right conditions, you can enjoy the beautiful blooms of lobelia throughout the summer.

Is Lobelia a Perennial?

The answer to whether lobelia is a perennial depends on the specific variety of lobelia you are referring to. Lobelia is a diverse genus of plants that includes both perennial and annual species, each with its unique characteristics.

  • Perennial Lobelia: There are several perennial varieties of lobelia, such as Lobelia cardinalis (Cardinal Flower) and Lobelia siphilitica (Great Blue Lobelia). These perennials are known for their striking spikes of flowers and can return year after year in the right growing conditions. In the UK, these perennial lobelias are hardy and can survive the winter, especially if provided with some protection in colder regions.
  • Annual Lobelia: On the other hand, the popular Lobelia erinus is typically grown as an annual. This variety is known for its cascading habit and profuse flowering, making it a favourite for hanging baskets and containers. While it blooms throughout the summer, it does not survive the winter and needs to be replanted each year.
  • Biennial Behavior: In some cases, lobelia plants can behave as biennials, growing foliage in the first year and flowering in the second year before completing their lifecycle.

In summary, whether lobelia is a perennial or not depends on the species you choose. Perennial varieties like Lobelia cardinalis and Lobelia siphilitica offer a long-term presence in the garden, while annual types like Lobelia erinus provide a season-long display of blooms but need to be replanted each year.