Giant Knotweed (Reynoutria sachalinensis)

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Sunlight Prefers full sun to partial shade; tolerates light shade but exhibits reduced growth and flowering in dense shade

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Watering Water deeply when the top 5–7 cm of soil dries out; avoid waterlogging to prevent root rot

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Temperature Extremely cold-hardy to -20°C; thrives in temperate to cool climates and tolerates brief summer heatwaves

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Leaf: Large, heart-shaped, 15–30 cm long, dark green with pointed tips and smooth margins
Flower: Small, creamy-white, clustered in drooping, branched panicles up to 20 cm long
Stem: Hollow, reddish-brown, with distinct bamboo-like nodes

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Watering

Keep soil consistently moist during active growth periods

Fertilization

Diluted balanced liquid feed every 4 weeks. Cease fertilization in early autumn to prepare the plant for dormancy

Eggshell powder topdressing：Sprinkle finely ground, dried eggshells on the soil surface to boost calcium levels and deter slug damage

Pruning

Cut back dead, brown stems to ground level in late winter to encourage vigorous new spring growth
Excavate and remove spreading rhizomes annually to contain the plant's aggressive spread
Thin overcrowded clumps in early spring to improve airflow and reduce disease risk

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Warning: this plant may be toxic.

Pets & Humans

Pets: ASPCA-classified toxic; ingestion leads to oral pain, drooling, vomiting, and difficulty swallowing

Humans: Contains calcium oxalate crystals; ingestion causes oral and throat irritation, nausea in large quantities

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Culture: N/A

Usage: Ornamental foliage plant; limited traditional medicinal use in some East Asian regions