Cardinalflower
Lobelia cardinalis · Cardinal FlowerUSDA | Grow Zone
3-9Outdoors all year in zones 3 to 9. Anywhere colder, keep it as a houseplant. Protect it below 40°F.
- Light
- Partial shade to full sun
- Water
- Consistently moist soil
- Humidity
- 50-70%
- Temperature
- 60-75°F (15-24°C)
- Difficulty
- Intermediate
- Growth
- Moderate
- Mature size
- 2-4 ft tall, 1-2 ft wide
- Pets
- Non-toxic to pets and children
Lobelia cardinalis, commonly known as Cardinalflower, is a stunning perennial native to North America. Its vibrant red flowers attract hummingbirds and add a splash of color to gardens, thriving in moist, partially shaded areas.
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Ideal temperature
60-75°F is where it grows fastest. Below 40°F cold damage starts.
Spacing and harvest
- Mature size
- 2-4 ft tall, 1-2 ft wide
- Plant apart
- 12-24 in
- Frost
- Half hardy: light frost only
Everything it needs
9 essentials at a glance
Watering
Lobelia cardinalis prefers consistently moist soil, especially during the growing season.
Water the plant deeply once a week, ensuring the soil remains damp but not waterlogged. In hotter months, you may need to water more frequently. Signs of over-watering include yellowing leaves and root rot, while under-watering can cause wilting and browning leaf edges.
Light
This plant thrives in partial shade to full sun, ideally receiving 4-6 hours of direct sunlight daily.
In hotter climates, it benefits from some afternoon shade to prevent leaf scorch. Ensure it is placed where it can receive filtered light, especially during the peak summer months.
Soil
Lobelia cardinalis prefers rich, well-draining soil with a pH range of 6.0 to 7.0.
A mix of loamy soil with organic matter, such as compost or peat moss, is ideal. Good drainage is crucial to prevent root rot, so consider adding perlite or sand to improve aeration.
Humidity
This plant enjoys moderate to high humidity levels, ideally between 50-70%.
To increase humidity, you can mist the leaves regularly or place a humidity tray filled with water and pebbles beneath the pot. Signs of low humidity stress include browning leaf tips and wilting.
Temperature
Lobelia cardinalis thrives in temperatures ranging from 60-75°F (15-24°C).
It is hardy in USDA zones 3-9, tolerating light frosts but not extreme heat. During hot summer months, ensure the plant is kept cool and well-watered to prevent heat stress.
Fertilizing
Use a balanced, water-soluble fertilizer with an NPK ratio of 10-10-10, applying every 4-6 weeks during the growing season.
In fall, reduce feeding as the plant prepares for dormancy. Signs of nutrient deficiency include stunted growth and yellowing leaves.
Pruning
Prune Lobelia cardinalis in early spring before new growth begins.
Remove any dead or damaged stems to encourage healthy growth. Deadheading spent flowers during the blooming season can promote further flowering and maintain the plant's appearance.
Repotting
Repotting is typically needed every 2-3 years or when the plant becomes root-bound.
Signs include roots growing out of the drainage holes or stunted growth. Choose a pot 1-2 inches larger in diameter, and gently loosen the roots before placing it in fresh soil.
Propagation
Propagation can be achieved through seeds or division.
For seeds, sow them in early spring, lightly covering them with soil and keeping them moist until germination. For division, carefully separate established clumps in early spring or fall, ensuring each division has roots and foliage. Replant immediately in suitable soil.
When it's unhappy
Yellow leaves
Why it happens
This can be caused by over-watering or nutrient deficiency.
How to fix it
Check the soil moisture and adjust watering frequency. Consider fertilizing if nutrient deficiency is suspected.
Wilting
Why it happens
Wilting can occur due to under-watering or extreme heat.
How to fix it
Ensure consistent moisture in the soil and provide shade during the hottest part of the day.
Root rot
Why it happens
Root rot is often caused by overly wet soil and poor drainage.
How to fix it
Improve drainage by adding perlite to the soil mix and reduce watering frequency.
Browning leaf tips
Why it happens
This can indicate low humidity or over-fertilization.
How to fix it
Increase humidity levels and reduce fertilizer application if browning occurs.
Pest infestations (aphids, spider mites)
Why it happens
Pests can thrive in warm, dry conditions.
How to fix it
Regularly inspect the plant, and treat infestations with insecticidal soap or neem oil.
Care through the year
Spring
In spring, prune back any dead stems and prepare for new growth. Fertilize with a balanced fertilizer to promote healthy foliage and blooms.
Summer
During summer, ensure consistent moisture and provide some afternoon shade in hotter climates. Deadhead spent flowers to encourage more blooms.
Fall
In fall, reduce watering as the plant prepares for dormancy. Consider mulching around the base to protect roots from frost.
Winter
In winter, protect the plant from extreme cold by covering with mulch. Reduce watering significantly, allowing the soil to dry out between waterings.
Toxicity & Safety
Lobelia cardinalis is considered non-toxic to pets and children. However, ingestion of large quantities may cause mild gastrointestinal upset. Always monitor children and pets around plants.
Good to know
How often should I water my Lobelia cardinalis?
Water your Lobelia cardinalis once a week, ensuring the soil remains consistently moist but not waterlogged. Adjust frequency during hotter months as needed.
What light conditions are best for Lobelia cardinalis?
Lobelia cardinalis thrives in partial shade to full sun, ideally receiving 4-6 hours of direct sunlight daily. In hotter climates, some afternoon shade is beneficial.
How do I propagate Lobelia cardinalis?
You can propagate Lobelia cardinalis through seeds or division. Sow seeds in early spring or divide established clumps in spring or fall for best results.
What type of soil is best for Lobelia cardinalis?
Lobelia cardinalis prefers rich, well-draining soil with a pH range of 6.0 to 7.0. A mix of loamy soil with organic matter is ideal for healthy growth.
Why are my Lobelia cardinalis leaves turning yellow?
Yellow leaves can indicate over-watering or nutrient deficiency. Check soil moisture levels and consider fertilizing if necessary.
When should I prune my Lobelia cardinalis?
Prune Lobelia cardinalis in early spring before new growth begins. Remove any dead or damaged stems to encourage healthy growth.
What are the common pests affecting Lobelia cardinalis?
Common pests include aphids and spider mites. Regularly inspect your plant and treat infestations with insecticidal soap or neem oil.
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