Lobelia Laxiflora Care: Tips On Growing The Mexican Cardinal Flower

Lobelia laxiflora [low-BEE-lee-a, laks-ih-FLO-ruh] is a flowering plant native to the Americas. 

This Lobelia plant species is found throughout parts of South and Central America and reaches as far north as Arizona in the US.

Blooming Mexican Cardinal Flower (Lobelia Laxiflora)
Magnus Manske [CC BY-SA 3.0], via Wikimedia Commons

For many years, people have used the plant for its medicinal alkaloids.

The laxiflora species has a few common names:

  • Mexican lobelia
  • Mexican cardinal flower
  • Sierra Madre lobelia
  • Loose flowers lobelia 
  • Drooping lobelia

It’s part of the Campanulaceae (bellflower) family and often grows as a perennial herb or sub-shrub. 

Lobelia Laxiflora Care

Size and Growth

Lobelia laxiflora develops slim green stems and thin green leaves. The stems eventually become woody and reddish, making the plant a sub-shrub. 

It’s a fast-growing plant which spreads through rhizomes growing underground. 

With proper care, it can reach heights of about 2’ – 3’ feet and achieve a spread up to 5’ feet. 

Flowering and Fragrance

The Mexican Lobelia produces tubular flowers at the end of each stem. 

They measure about 2” inches long and feature bright yellow and reddish-orange colors. The flowers first appear in the spring and last through the fall. 

In ideal environments, such as the Southwestern United States, the plant stays in bloom almost all year.

Light and Temperature

For best results, grow the plant under full sun or partial shade. It’s suited for USDA hardiness zone 9 to 11. 

In areas with cooler weather or less mild climates, the plant requires overwintering and planting in a container. 

Place it in a spot where it receives full sun, but not direct afternoon sunlight such as through the south or east-facing window.

Watering and Feeding

Younger plants require deep watering throughout the summer. Thoroughly saturate the soil and prevent it from going completely dry.

Once established, the plant is drought tolerant and doesn’t need frequent watering. Excess watering promotes faster growth, allowing the plant to spread faster. Keep established plants on the dry side.

Soil and Transplanting

Use well-drained soil for optimal growth. However, the plant doesn’t require perfect conditions. 

It grows well in almost any soil if it gets enough sun and water.

If growing the plant in a container, don’t transplant unless it needs a larger pot. 

Transplant in the spring, just before new growth starts. 

When selecting a pot, choose a size slightly smaller than normal for a plant of its size. 

The plant grows when it partially develops a root ball.

Grooming

Without grooming, this deer resistant plant may become invasive and spread through the garden. 

Look for new growth appearing from rhizomes growing underground. Cutaway the growth to prevent the spread of the plant.

To manage the overall size of the laxifloras, trim back the branches in the fall after the flowering season. 

This encourages renewal in the spring and makes it easier to maintain a smaller size.

Grooming is especially helpful with container plants, as lobelia laxiflora may reach up to 3’ feet tall.

Other Lobelia Of Interest:

How to Propagate Lobelia Flower

Propagate the Lobelia flower with cuttings in the late spring, when grooming the plant. 

  • Choose branches having not yet flowered. 
  • Cut 4” – 5” inches of a branch and remove the leaves. 
  • Take several cuttings to ensure at least one matures.
  • Prepare a clay pot with well-drained potting soil. 
  • Water the soil and then push the cuttings about halfway into the pot. 
  • Pressing the cuttings into the soil at least halfway provides support as they slowly take root.
  • Mist the cuttings with water twice per day and water the container every other day. 
  • The cuttings require constant moisture.
  • When the cuttings take root, replant them in new containers. 
  • After the last threat of frost, transplant young plants intended for outdoor growth to the garden. 

Drooping Lobelia Pest or Diseases

Hummingbirds flock to this plant but don’t pose a threat. 

The main pests to worry about include:

If detected early, remove the pests using cotton swabs. 

Dip the swabs in rubbing alcohol and wipe the leaves and stems to get rid of the infestation. 

If the infestation spreads, use an insecticide (neem oil) or wash away the pests with sprays from a garden hose, using caution to avoid damaging the branches.

Besides the typical pests and diseases, watch out for children and pets. 

Parts of the plant contain toxins which may be poisonous to humans and animals. 

The plant isn’t an invasive species but is invasive in the garden. 

It spreads with rhizomes, which may eventually overtake adjacent plants or weeds.

Suggested Lobelia Laxiflora Uses

In warmer climates, grow the Sierra Madre Lobelia flower outdoors, where it can reach its full size. 

It forms a dense ground cover, often used toward the back of the garden behind shorter plants.

In cooler regions, manage the growth and keep it in a large pot. 

Showcase the flowers on a patio or porch during the summer before overwintering the plant.