Horned Mustard (Sisymbrium polyceratium)

Horned Mustard

Sisymbrium polyceratium

It bears delicate yellow blooms atop slender stems, a cheerful wild annual. Wild mustard species; common name: horned mustard.

Full sun
1–2/week
Beginner
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Plant Needs

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Sunlight Full sun to partial shade; performs best in unobstructed sunlight for robust flowering and compact growth
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Watering Water deeply when the top 2–3 cm of soil feels dry; drought-tolerant once established, so avoid overwatering
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Temperature Thrives in cool to warm temperate temperatures; tolerates light spring or autumn frost without significant damage
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Characteristics

  • Leaf: Basal rosette of lobed, hairy leaves; stem leaves are smaller, linear and sparsely hairy
  • Flower: Small, four-petaled yellow blooms arranged in elongated terminal racemes
  • Stem: Slender, branching green stems covered in fine, stiff hairs
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Care Guide

Watering

Keep soil moderately moist during active growth and flowering periods

Fertilization

Apply a diluted balanced organic feed once per month. Avoid high-nitrogen fertilizers, which can promote excessive foliage growth over flowering

Eggshell powder topdress:Sprinkle finely ground, oven-dried eggshells around the base of the plant to boost soil calcium levels and improve drainage; avoid direct contact with stems to prevent fungal growth
Pruning
  • Deadhead spent flower racemes regularly to encourage extended blooming and prevent unwanted self-seeding
  • Remove yellowing or damaged basal leaves to improve airflow and reduce disease risk
  • Cut back entire stems to ground level after the plant has finished seeding to clear garden space for new plantings
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Toxicity

Warning: this plant may be toxic.

Pets & Humans

Pets: ASPCA notes that some Brassicaceae species may cause mild gastrointestinal upset (vomiting, diarrhea) if ingested in significant amounts

Humans: Ingestion of large quantities may cause mild gastrointestinal irritation, including nausea and stomach cramping

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Garden Uses & Culture

Culture: N/A

Usage: Used as a wild forage crop in some regions; grown as an ornamental wildflower in native pollinator gardens