How to grow blue devil
Overview
Blue devil (Eryngium ovinum) is a herbaceous perennial native to southeastern Australia, grown for its striking spiky blue flower heads and silvery-green foliage. It thrives in dry, sunny native gardens and requires excellent drainage to avoid root rot.
Soil Preparation
Blue devil prefers a neutral to slightly acidic pH (6.0–7.0) in sandy or loamy soil that drains freely. Add coarse sand or gravel to heavy clay before planting. Avoid organic-rich compost that retains moisture.
Growing Guide
Plant blue devil in full sun in a free-draining, sandy or gravelly soil. Space plants 40–50 cm apart to allow for clump spread. Sow seed directly in autumn or early spring; do not cover seed as it needs light to germinate. Avoid overwatering — let the soil dry between drinks. It is drought-tolerant once established and resents wet feet.
Sowing
Sow seed on the surface of a seed-raising mix in autumn or early spring; do not cover as light aids germination. Germination takes 14–21 days at 15–20°C. Thin seedlings to 40 cm apart. Direct sowing is preferred over transplanting.
Care
Feed with a low-nitrogen native plant fertiliser in early spring. After flowering, cut spent stems to the base to keep the plant tidy and prevent self-seeding. No additional pruning or staking is needed.
Companion Planting
Blue devil pairs well with native grasses such as Poa labillardieri and Themeda triandra, and with other low-water perennials like kangaroo paw (Anigozanthos) and paper daisy (Rhodanthe). Avoid planting near moisture-loving vegetables or in rich, heavy clay that stays wet.
Common Pests & Risks
Blue devil is generally pest-free. In humid conditions, watch for aphids on new growth — hose off or use a weak soap spray. Snails and slugs may attack young seedlings; protect with grit or organic pellets. No serious diseases if drainage is adequate.
Troubleshooting
Yellow leaves: overwatering or poor drainage — reduce water and check soil. Stunted growth: too much shade — move to full sun. Leggy stems: excess nitrogen — switch to low-N native fertiliser. Seedlings fail to emerge: seed buried too deep — surface-sow only.