How to Grow Lobelia

If I had to pick a favorite flower, lobelia might be it. The intense blue of this dainty-looking annual flower adds a lovely pop of color to raised beds and containers. Lobelia blooms are a profusion of small tubular flowers that come in blue, white, magenta, or purple. These four tips teach you how to grow and add lobelia to your garden or containers. 

4 Tips for How to Grow Lobelia

1. Grow lobelia from seed or transplant

Start seeds indoors 6-8 weeks before planting outside. Press seeds into the soil but do not cover; they need light to germinate. 

When buying transplants, look for compact, healthy transplants with few blooms, stocky stems, and deep-green leaves. Avoid plants with faded flowers or yellow foliage. 

Varieties to try: 

• Crystal Palace – Classic, compact lobelia with dark blue flowers. Click here for seeds.
• Fountain (Lilac, White) – Trailing more heat-tolerant types. Click here for seeds.
• Cascade of Color – Trailing multi-colored variety. Click here for seeds.

2. Plant lobelia at the right time

In most locations, plant lobelia transplants in the spring after the danger of frost has passed. Lobelia blooms from early summer through the first frost in places with mild summer climates. After frost, pull up the dead plants and add them to the compost pile. 

Plant lobelia from late September through December in hot summer climates. Lobelia blooms from early spring until temperatures soar in June. Plant lobelia in shady locations to keep lobelia alive longer. 

When to plant lobelia in Arizona

Start seeds indoors:
July – October
Plant transplants outside:
September 15 – December

The Perpetual Annual Flower Planting Calendar, available in my shop, helps you learn when to plant flowers in the low desert of Arizona and whether to plant seeds or transplants.

3. Plant lobelia in the ground or in containers

Lobelia plants are 4-24” wide and 4-8” tall. They are an excellent choice for tucking in around other larger plants and the outside edges of raised beds and containers. Lobelia’s compact size makes it a perfect choice for growing in containers.

My favorite plant combination is lobelia, planted with blue salvia. They look so good grown together. I find myself adding that combination all over my yard.

• Lobelia prefers moist, rich, well-draining soil. Amend the planting area with compost before planting.
• Choose a location with partial sun (4-6 hours); morning sun is ideal.  
• Mulch plants well after planting to conserve moisture and keep the soil cool.
• Feed with a fish fertilizer after planting to encourage growth and blooms. 
• Shade newly-planted seedlings for the first several days.

4. Care for lobelia as it grows

• Lobelia can become heat-stressed during hot spells. Give plants additional water. 
• Cut back spent blooms regularly to encourage more flowers. 
• All parts of lobelia are poisonous. Keep plants away from pets and children. 
• Allow the plant to drop seeds, and it may reseed the following season.
• If you use lobelia as a cut flower, hold the stem in a flame for 15 seconds immediately after cutting to seal the latex in the stem. This prevents the sap from leaking into the water (shortening the vase life) and keeps the water-conducting vessels open.

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