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Artistic illustration of green leaves on a beige background

Blue Oil Fern

SCIENTIFIC NAME: Microsorum thailandicum

KNOWN AS: Blue Oil Fern, Steere's Fern

CLIMATE (LOCATION): Southeast Asia (Thailand, Vietnam, Laos) | Tropical Rainforest (Epiphyte/Lithophyte)

DESCRIPTION: The Blue Oil Fern is one of the most mesmerizing plants in the world. Its leathery, strap-like fronds possess a stunning metallic blue iridescence. This isn't a pigment, but a biological trick: the plant uses "iridoplasts" to slow down light and capture more energy in the dim rainforest understory. Under a flashlight or bright indirect light, the leaves glow with an electric, neon-blue "oil slick" sheen.

Blue Oil Fern Plant Care

Lighting

Light Requirement: Medium Light (Medium Indirect Light); Low Light Tolerant

This is a deep-shade specialist.

The Secret: The blue iridescence is actually a defense mechanism for low light. If you give it too much light, the plant will turn a standard forest green and lose its blue glow.

Direct Sun: Lethal. Even an hour of direct sun will bleach the fronds and destroy the iridoplasts.

The Goal: A north-facing window or a dim corner where it can "hunt" for light is perfect.

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Watering

Quick Tip: Keep the soil consistently moist, but not waterlogged.

Unlike many ferns, the Blue Oil Fern has thicker, leathery leaves, but its roots are very fine and sensitive.

The Routine: Water when the very surface of the soil feels slightly dry. If the soil becomes bone-dry, the fronds will crisp up and the plant may not recover.

Water Quality: It is moderately sensitive to chemicals. Using filtered or rainwater will help prevent brown spots on those precious blue leaves.

Temperature

Preferred Temperature: 65º - 80º

This is a tropical plant that thrives in warmth.

Cold: It hates temperatures below 60°F. Cold drafts will cause the blue sheen to dull and can lead to root death.

Stability: It prefers a stable environment. Keep it away from AC units or heaters that cause rapid temperature swings.

Humidity

Preferred Humidity: 60 - 80%; High Humidity

This is the most critical factor for success.

The Problem: In dry indoor air, the tips of the fronds will turn black or brown, and the blue glow will fade.

The Solution: A humidifier is highly recommended. Because it is often grown as an epiphyte (on bark or in chunky mixes), it loves humid air circulating around its roots and leaves. It is a perfect candidate for a terrarium or glass cabinet.

Additional Plant Care

Propagation
The Blue Oil Fern grows from a creeping rhizome (a furry root-like stem). How to Propagate: Rhizome Division. During repotting, look for a section of the rhizome that has at least 2–3 fronds and its own set of roots. Carefully snip it with sterilized shears. Tip: Pin the rhizome to the surface of the new soil rather than burying it; burying the rhizome can cause it to rot.
Toxicity
Quick Warning: Non-Toxic to cats, dogs, and humans. Safe for pets, but because this is a rare and slow-growing plant, you’ll want to keep it out of reach of "nibblers" to preserve its beauty.
Repotting
When to Repot: Every 2–3 years. It is a slow grower and prefers to stay somewhat snug. Choose a Pot: Use a shallow pot or an orchid basket. It has shallow roots and doesn't need a deep reservoir of soil. Soil: Do not use standard potting soil (it's too heavy).
Pruning
Grooming: Remove old, brown fronds by cutting them at the base of the rhizome. Cleaning: Dust interferes with the plant’s ability to reflect blue light. Very gently wipe the leaves with a damp cloth or a soft makeup brush. Do not use leaf shine.
Fertilizing
Quick Tip: Feed very weakly; ferns are sensitive to salt. What to Use: A liquid seaweed or balanced fertilizer diluted to 1/4 strength. When to Apply: Once a month during the spring and summer. The Danger: Over-fertilizing will burn the delicate roots and can cause the blue color to turn a muddy brown. Always water with plain water before adding fertilizer. Winter: Stop fertilizing entirely in the winter.
Soil
In the wild, this fern grows on rocks or tree trunks. It needs an "ultra-airy" mix. Ideal Mix: An Epiphytic or Orchid-style mix. Recommended Blend: 1 part long-fiber sphagnum moss, 1 part orchid bark, and 1 part perlite. This allows the roots to stay moist but provides the heavy aeration they require to prevent rot.

Hanging Heights

Blue Oil Fern Lighting Requirements: Medium Light (Medium Indirect Light); Low Light Tolerant

Chart showing recommended hanging heights for Soltech Aspect and popular plants for each range.

Aspect Hanging Heights - Blue Oil Fern

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Soltech's Recommendation -

48"-72"

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VIEW ASPECT GROW GUIDE

Vita Hanging Heights - Blue Oil Fern

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Soltech's Recommendation -

36º Narrow Beam Vita : Not Recommended

60º Wide Beam Vita : Not Recommended

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VIEW VITA GROW GUIDE

Highland Hanging Heights - Blue Oil Fern

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Soltech's Recommendation -

36º Narrow Beam Highland : Not Recommended

60º Wide Beam Highland : Not Recommended

-

VIEW HIGHLAND GROW GUIDE

Grove Hanging Heights - Blue Oil Fern

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Soltech's Recommendation:

  • 12" to 24"

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VIEW GROVE GROW GUIDE

Lighting guide for plants with Soltech Aura and potted plants on a neutral background

Aura Light Distances - Blue Oil Fern

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Soltech's Recommendation:

  • 8" to 18"

-

VIEW AURA GROW GUIDE

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