PlantFun
Plant Needs
Sunlight
Full sun to partial shade; thrives in bright, direct sunlight and tolerates hot afternoon sun in cool temperate regions
Watering
Water deeply when the top 2–3 cm of soil dries out; avoid overwatering to prevent root rot
Temperature
Extremely cold-hardy down to -30°C; tolerates moderate summer heat, with reduced growth during prolonged extreme drought
Characteristics
- Leaf: Narrow lanceolate leaves with serrated margins, medium green, arranged oppositely on stems
- Flower: Dense terminal spikes of small tubular blue (rarely pink/white) flowers with four petals
- Stem: Erect, slender green stems branching near the base
Care Guide
Watering
Keep soil evenly moist during active growth; avoid waterlogging
Fertilization
Top-dress with compost at the start of growing season. Avoid high-nitrogen fertilizers to prevent leggy, floppy stems
Eggshell powder top-dress：Crush clean, dried eggshells into fine powder; sprinkle 1 tbsp per plant in early spring and work lightly into topsoil to boost soil calcium levelsPruning
- Deadhead spent flower spikes to encourage continuous reblooming into late summer
- Cut back stems to 5 cm above soil level in late autumn after foliage dies back
- Thin overcrowded clumps every 2–3 years in early spring to improve airflow and reduce disease risk
Toxicity
Warning: this plant may be toxic.
Pets & Humans
Pets: ASPCA-verified non-toxic to cats; no reported toxicity symptoms
Humans: Non-toxic to humans; no known adverse health effects from ingestion or contact
Garden Uses & Culture
Culture: Symbolizes fidelity and loyalty in Victorian floriography
Usage: Ornamental garden plant; attracts bees, butterflies, and other pollinators
