Giant Fennel (Ferula glauca)

Giant Fennel

Ferula glauca

Its silvery-blue foliage carries dryland elegance, a sculptural focal point in arid gardens. Evergreen perennial herb; common name: Giant Fennel.

Full sun
0–1/week
Moderate
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Plant Needs

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Sunlight Requires full sun exposure to maintain silvery foliage color; tolerates reflected heat in arid climates
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Watering Drought-tolerant; water deeply only when the top 15–20 cm of soil is completely dry to avoid root rot
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Temperature Hardy to mild frosts; thrives in hot, dry summer temperatures typical of Mediterranean climates
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Characteristics

  • Leaf: Silvery-blue, finely divided, feathery foliage forming a dense basal clump
  • Flower: Tall, branching umbels of tiny yellow flowers on sturdy, glaucous stems
  • Stem: Thick, fleshy pale green stems with a powdery, silvery glaucous coating
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Care Guide

Watering

Water deeply once every 2–3 weeks during active growth periods

Fertilization

Apply diluted balanced organic feed once in early spring. Avoid high-nitrogen fertilizers to prevent leggy growth

Eggshell powder topdress:Crush dried, clean eggshells to a fine powder; sprinkle lightly on the soil surface around the base of the plant to add calcium without altering soil composition
Pruning
  • Remove spent flower stems after blooming to maintain a tidy clump and redirect energy to foliage growth
  • Trim damaged or browned foliage at the base in early spring before new growth emerges
  • Divide overcrowded clumps every 3–4 years in early spring to improve airflow and vigor
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Toxicity

Warning: this plant may be toxic.

Pets & Humans

Pets: ASPCA: No listed toxicity to cats

Humans: No documented toxicity to humans when handled or ingested in typical quantities

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Garden Uses & Culture

Culture: N/A

Usage: Ornamental focal plant in xeric gardens; silvery foliage used in dried floral arrangements