Blue Sea Holly
eryngium planum
Also known as: ["Blue Eryngo","Flat Sea Holly"]
Overview
A striking perennial with spiky, thistle-like blue flowers and silvery foliage, native to Europe and Asia.
Benefits & Perks
["long-flowering","deer resistant","wildlife attractant (bees, butterflies, birds)","drought tolerant","aesthetic foliage"]
Botanical Classification
| Phylum: | Magnoliophyta |
| Class: | Magnoliopsida |
| Order: | Apiales |
| Family: | Apiaceae |
| Genus: | Eryngium |
| Botanical Name: | Eryngium planum |
Plant Characteristics
Basic Information
- Category: Flowers
- Suitable Location: garden border or rock garden in full sun
- Suitable For:
- Is Weed: No
- Allergenicity: low
Environmental Needs
- Climate: {"temperatureRange":"5–35°C"}
- Hardiness: {"zones":"4–9"}
- Misting: rarely required, only if ambient humidity is very low
- Drainage: Fast-draining.
- Soil Type: Well-draining, sandy loam with some organic matter. Avoid heavy clay soils.
Maintenance Level
- Maintenance Level: low
- Toughness Level: high
- Pruning Frequency: Deadhead spent flowers as needed; prune lightly in early spring.
- Pruning Intensity: Light to moderate. Avoid heavy pruning unless rejuvenating an older plant.
Care Details
Ideal Sunlight Coverage:
Full sun (6–8 hours of direct sunlight daily). Tolerates partial shade but may produce fewer flowers.
Sunlight Tolerance Tips:
Acclimate plants gradually if moving from shade to sun. Protect from intense midday sun in hot climates. Ensure good air circulation to prevent fungal issues in humid conditions.
Care Requirements
Care Difficulty
easymoderate
Sunlight
full sun
Full sun is best; rotate pots for even growth; avoid deep shade.
Watering
every 7–10 days during active growth, less frequently in winter
Water thoroughly but infrequently; allow soil to dry between waterings; avoid overwatering to prevent root rot.
Soil
well-drained, sandy loam with moderate fertility
pH: Slightly alkaline to neutral (pH 6.5–7.5).
Ensure excellent drainage; avoid waterlogged soil; enrich with compost if needed.
Temperature
Hardy in USDA zones 3–9. Prefers cool to moderate temperatures (60–75°F or 15–24°C). Tolerates frost but may struggle in extreme heat.
Protect from frost; water deeply in heat; ensure good air flow.
Fertilizing
every 4–6 weeks during spring and summer
Fertilize sparingly; avoid high-nitrogen formulas; stop in late summer.
Propagation
Methods
Stem cuttings or division. Stem cuttings are more common for home growers.
Step-by-Step Propagation Guide
- Take 4–6 inch cuttings.
- Remove lower leaves.
- Dip in rooting hormone.
- Plant in medium.
- Keep moist and humid.
Best Time: Early summer when the plant is actively growing.
Environment
Warm (70–75°F or 21–24°C), high humidity (70–80%), and bright indirect light.
Medium
Well-draining mix of perlite and peat moss or cactus mix.
Hormone
Recommended to use rooting hormone for better success.
Timeline
Roots develop in 3–4 weeks; plants establish in 2–3 months.
Tools Needed
Pruning shears, rooting hormone, small pots, misting spray bottle.
Quick Tips
Use healthy, non-flowering stems; maintain humidity with a plastic cover; keep out of direct sun.
Pruning & Repotting
Pruning Guide
Method
Pinch back tips for bushier growth; cut spent flowers just above a leaf node.
Pruning Plan
Prune to maintain shape, encourage bushier growth, and remove spent flowers for prolonged blooming.
Tools
Pruning shears, gloves, disinfectant for tools.
Checklist
Use clean tools; prune dead or damaged stems; remove spent flowers; shape as desired.
Repotting Guide
Best Season
Early spring before new growth begins.
Pot Size
One size up (e.g., from 4-inch to 6-inch pot); ensure good drainage holes.
Method
Gently remove the plant; trim any dead roots; place in a slightly larger pot with fresh, well-draining soil; water thoroughly.
Suggestions
Repot every 2–3 years or when roots fill the container. Eryngium planum is generally hardy and does not require frequent repotting.
Checklist
Choose appropriate pot size; use fresh soil; trim roots if necessary; water after repotting.
Advanced Care Tips
Watering Mastery
Watering Checklist
Check soil moisture before watering; water deeply; ensure drainage; avoid wetting leaves.
How to Apply Water Properly
Water at the base of the plant, ensuring moisture reaches the root zone. Water early in the morning to minimize evaporation and fungal issues. Ensure excess water drains away to prevent waterlogging.
Watering Schedule Tips
Water deeply once every 7–10 days during active growth, reducing frequency to every 2–3 weeks in winter. Adjust based on rainfall and soil dryness.
Soil Improvement
Add perlite or coarse sand to improve drainage; incorporate compost for fertility.
Temperature Stress Management
Signs of Temperature Issues
Chlorosis or wilting in excessive heat; stunted growth or bud drop in cold stress.
Cold Stress
Low temperatures slow growth but are generally tolerated. Prolonged freezing may damage foliage but usually recovers in spring.
Solution: Mulch around the base in winter to insulate roots. Avoid planting in areas prone to frost pockets.
Hot Stress
Excessive heat can cause wilting, leaf scorch, or reduced flowering.
Solution: Provide afternoon shade in hot climates; water deeply to cool roots; improve air circulation.
Fertilizing Guide
Fertilizing Checklist
Use diluted fertilizer; apply during growing season; avoid winter feeding.
Fertilizing Method
Use a balanced, water-soluble fertilizer diluted to half strength every 4–6 weeks during spring and summer. Avoid fertilizing in fall and winter.
Common Problems & Solutions
Toxicity Warning
Cats
Non-toxicEryngium planum is not considered toxic to cats. The plant does not contain any known substances that are harmful to felines, and ingestion is not expected to cause adverse effects.
⚡ Toxic If:
Generally non-toxic
Dogs
Non-toxicEryngium planum is not considered toxic to dogs. The plant does not produce any known compounds that are harmful to canines, and ingestion is not expected to cause adverse effects.
⚡ Toxic If:
Generally non-toxic
Humans
Non-toxicEryngium planum, commonly known as blue eryngo, is not considered toxic to humans. It is a flowering plant in the Apiaceae family and is often used in ornamental gardens for its striking blue flowers. There are no known toxic effects or physiological impacts associated with this plant.
⚡ Toxic If:
Generally non-toxic
Frequently Asked Questions
Q: Does Eryngium planum attract pollinators?
A: Yes, it is highly attractive to bees, butterflies, and other pollinators.
Q: Is this plant drought-tolerant?
A: Yes, it thrives in dry conditions and requires minimal watering once established.
Q: How should I propagate Blue Sea Holly?
A: It can be propagated by seed in spring or by division in early autumn.
Quick Reference
| Family: | Apiaceae |
| Care: | easy |
| Light: | full sun |
| Water: | every 7–10 days during activ |
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