Great Lobelia

lobelia siphilitica

Also known as: ["Blue Cardinal Flower","American Lobelia"]

Family: Campanulaceae Genus: Lobelia Category: Flowers

Overview

A herbaceous perennial native to North America, known for its striking spikes of bright blue flowers in late summer.

Benefits & Perks

["long-flowering","wildlife attractant (bees, butterflies, birds)","shade tolerant"]

Botanical Classification

Phylum: Magnoliophyta
Class: Magnoliopsida
Order: Asterales
Family: Campanulaceae
Genus: Lobelia
Botanical Name: Lobelia siphilitica

Plant Characteristics

Basic Information
  • Category: Flowers
  • Suitable Location: border gardens, woodland edges, or containers with consistent moisture
  • Suitable For:
    Beginners Outdoor Landscapers Wildlife Supporters
  • Is Weed: No
  • Allergenicity: low
Environmental Needs
  • Climate: {"temperatureRange":"5–30°C"}
  • Hardiness: {"zones":"3–8"}
  • Misting: rarely required, only if ambient humidity is very low
  • Drainage: Moderately well-draining; avoid heavy clay soils.
  • Soil Type: Rich, loamy soil with good organic matter; well-draining but moisture-retentive.
Maintenance Level
  • Maintenance Level: moderate
  • Toughness Level: moderate
  • Pruning Frequency: After flowering; as needed to remove dead or damaged growth.
  • Pruning Intensity: Light to moderate; avoid heavy pruning unless necessary to control size.
Care Details

Ideal Sunlight Coverage:
Full sun to partial shade (4–6 hours of direct sunlight daily); tolerates partial shade in hotter climates.

Sunlight Tolerance Tips:
Acclimate gradually to direct sun if moving from shade; protect from intense midday sun; ensure good air circulation to prevent scorching.

Warning Signs: Yellowing leaves (overwatering or poor drainage), stunted growth (nutrient deficiency), or wilting (underwatering or root rot).

Care Requirements

Care Difficulty
moderate

moderate

Sunlight

partial shade to full sun

Morning sun is ideal; provide shade during peak afternoon heat; rotate pots for even growth.

Watering

every 7–10 days, more frequently in hot, dry conditions

Keep soil consistently moist but not waterlogged; avoid overhead watering to prevent fungal issues; ensure good drainage.

Soil

moist, rich, well-drained loam

pH: Slightly acidic to neutral (pH 6.0–7.0).

Avoid waterlogging; ensure soil is not compacted; use mulch to retain moisture.

Temperature

Prefers cool to moderate temperatures (60–75°F or 15–24°C); thrives in cooler summers and can tolerate light frost.

Avoid sudden temperature fluctuations; protect from drafts; maintain consistent humidity.

Fertilizing

every 4–6 weeks during active growth (spring and summer)

Fertilize after watering to prevent root burn; stop fertilizing when plant is dormant; use organic options like compost tea.

Propagation

Methods

Stem cuttings or division of clumps; seeds can also be sown in early spring.

Step-by-Step Propagation Guide
  1. Take 4–6 inch cuttings.
  2. Remove lower leaves.
  3. Dip in rooting hormone (optional).
  4. Plant in medium.
  5. Keep moist and humid.

Best Time: Early spring or late summer when the plant is actively growing.

Environment

High humidity (70–80%), indirect light, and consistent warmth (65–70°F or 18–21°C).

Medium

Well-draining potting mix with perlite or sand; peat moss can help retain moisture.

Hormone

Rooting hormone is optional but can improve success rates.

Timeline

Roots may develop in 2–4 weeks; new growth appears in 6–8 weeks.

Tools Needed

Pruning shears, rooting hormone, small pots, misting spray bottle, plastic bags (for humidity).

Quick Tips

Use healthy, non-flowering stems; maintain humidity with a plastic dome; avoid direct sunlight.

Pruning & Repotting

Pruning Guide
Method

Deadhead by cutting just above a leaf node; trim stems to encourage bushier growth.

Pruning Plan

Remove spent flowers to encourage reblooming; trim leggy stems to maintain compact growth.

Tools

Clean, sharp pruning shears or scissors.

Checklist

Sterilize tools; prune in early morning; remove dead or diseased parts; avoid over-pruning.

Repotting Guide
Best Season

Early spring before new growth begins.

Pot Size

One size larger pot (e.g., +2 inches in diameter); ensure good drainage.

Method

Remove plant gently; trim roots if crowded; place in a slightly larger pot with fresh soil; water thoroughly.

Suggestions

Repot every 2–3 years or when roots fill the container; beneficial for container-grown plants to refresh soil.

Checklist

Choose appropriate pot size; use fresh, well-draining soil; water after repotting; avoid fertilizing for a month.

Advanced Care Tips

Watering Mastery
Watering Checklist

Check soil moisture daily; water early morning; ensure pots have drainage holes; adjust based on weather.

How to Apply Water Properly

Water at the base of the plant, targeting the root zone; water until it drains from the bottom; avoid wetting foliage.

Pro Tip: Use a watering can with a narrow spout to direct water to the roots without disturbing the soil surface.
Watering Schedule Tips

Water deeply once the top inch of soil feels dry; increase frequency during hot, dry periods; reduce in winter to prevent root rot.

Soil Improvement

Add compost or well-rotted manure for fertility; mix in perlite or sand for drainage; use peat moss for moisture retention.

Temperature Stress Management
Signs of Temperature Issues

Wilting, yellowing leaves, or stunted growth in excessive heat; leaf drop or browning in cold stress.

Cold Stress

Slows growth and may cause leaf damage below 50°F (10°C); prolonged cold can lead to root rot.

Solution: Provide frost protection in cold climates; ensure good drainage to prevent waterlogging; move potted plants indoors if temperatures drop below 40°F (4°C).

Hot Stress

Leaves may scorch, wilt, or drop in excessive heat; flowering may be reduced.

Solution: Provide partial shade during peak heat; increase watering frequency; use mulch to retain soil moisture.

Fertilizing Guide
Fertilizing Checklist

Check fertilizer label for NPK ratio; dilute correctly; apply to moist soil; avoid contact with foliage.

Fertilizing Method

Use a balanced liquid fertilizer diluted to half strength every 4–6 weeks during growing season (spring to early fall); avoid fertilizing in winter.

Common Problems & Solutions

Yellowing leaves in Lobelia siphilitica may indicate nutrient deficiencies, overwatering, or pest infestations, affecting the plant's photosynthetic efficiency and overall health.

Wilting in Lobelia siphilitica can result from water stress, either due to drought or overwatering, disrupting nutrient uptake and potentially leading to plant death if not addressed.

Leaf spots on Lobelia siphilitica may be caused by fungal or bacterial pathogens, leading to reduced photosynthesis and potential defoliation if severe.

Rotting, particularly root or stem rot, can occur in Lobelia siphilitica due to excessive moisture or fungal infections, leading to decay and eventual plant death.

Toxicity Warning

Cats
Toxic

Cats are highly sensitive to the toxic compounds in Lobelia siphilitica. Ingestion can lead to severe gastrointestinal and neurological effects, potentially resulting in life-threatening conditions.

⚠️ Symptoms:
vomiting diarrhea depression difficulty breathing muscle weakness seizures
🌿 Toxic Parts:
entire plant
⚡ Toxic If:

if eaten

Keep cats away from the plant. If ingestion is suspected, seek veterinary care without delay.
Dogs
Toxic

The alkaloids in Lobelia siphilitica can cause significant toxicity in dogs, affecting the respiratory and nervous systems. Symptoms can range from mild gastrointestinal upset to severe respiratory failure.

⚠️ Symptoms:
vomiting diarrhea lethargy difficulty breathing tremors seizures
🌿 Toxic Parts:
entire plant
⚡ Toxic If:

if eaten

If a dog ingests any part of the plant, contact a veterinarian immediately.
Humans
Toxic

Lobelia siphilitica contains lobeline and other alkaloids that act as respiratory stimulants and neuromuscular blockers. Ingestion can lead to severe physiological effects, including respiratory distress and central nervous system depression.

⚠️ Symptoms:
nausea vomiting diarrhea dizziness weakness respiratory depression convulsions
🌿 Toxic Parts:
entire plant
⚡ Toxic If:

if eaten

Keep out of reach of children. In case of ingestion, seek immediate medical attention.
Important: Keep this plant out of reach of children and pets. If ingestion occurs, contact poison control or veterinary services immediately.

Frequently Asked Questions

Q: Is Lobelia siphilitica toxic to pets?

A: Yes, it is mildly toxic to dogs and cats if ingested.

Q: Does Lobelia siphilitica attract wildlife?

A: Yes, it attracts bees, butterflies, and hummingbirds with its nectar-rich flowers.

Q: How should Lobelia siphilitica be watered?

A: It prefers consistently moist soil and should not be allowed to dry out completely.

Quick Reference
Family: Campanulaceae
Care: moderate
Light: partial shade to full sun
Water: every 7–10 days, more freque
Suitable For: ["beginners","outdoor landscapers","wildlife supporters (attracts bees, butterflies, birds)"]
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