Microsorum Siamensis

Microsorum Siamensis is an unusual tropical fern admired for its iridescent blue-green fronds. Its elongated, undivided leaves have gently rippled edges and pointed tips, creating a sleek silhouette. Under suitable conditions, the foliage develops a metallic blue sheen that makes it a striking addition to a fern collection.

Commonly sold as Microsorum Siamensis, its accepted botanical name is Microsorum siamense. It originates from southern Thailand, where it grows in shaded crevices on moist limestone rocks and cliffs. This habitat helps explain its preference for humid air, gentle light and excellent drainage.

The plant spreads slowly through creeping rhizomes, gradually forming a leafy colony. Its measured growth and humidity requirements make it particularly suited to terrariums, vivariums and carefully managed growing cabinets. The blue effect varies with lighting and viewing angle, so the same plant may appear greener from one position and more intensely blue from another.

Light

Provide low to moderate indirect light, avoiding strong direct sunshine. Filtered light beneath taller plants or a suitably positioned grow light can work well.

Excessive light can reduce the blue sheen and make the foliage appear greener. Avoid repeatedly moving the plant in search of stronger colour; allow it time to adjust to a stable position.

Watering

Keep the growing medium lightly moist, allowing the surface to begin drying between waterings. Avoid letting the entire root zone become completely dry.

Water carefully and allow surplus moisture to drain away. Although this fern enjoys humidity, its roots and rhizomes should not remain in saturated compost.

Check moisture regularly rather than following a fixed weekly schedule, especially inside a terrarium where evaporation may be slow.

Humidity

Provide consistently high humidity. Specialist growers recommend around 80% or higher, making an enclosed growing space particularly useful.

Maintain gentle air exchange within the enclosure. Humid conditions should be accompanied by drainage and airflow, rather than persistently stagnant, wet foliage.

Temperature

Keep the plant in a warm, stable indoor environment. A warm room or temperature-controlled growing cabinet is a practical choice.

Protect it from cold draughts, sudden temperature changes and direct heat from radiators. Take care that lighting does not overheat a small enclosure.

Potting mix

Use a loose, moisture-retentive but freely draining medium. A fine orchid-style mix containing bark, perlite and a modest moisture-retaining component is a practical starting point.

Specialist growers sometimes incorporate a small proportion of limestone chippings to reflect its natural habitat. Avoid dense compost or burying the creeping rhizome deeply; keep it close to the surface.

Water quality

Clean rainwater, distilled water or reverse-osmosis water can help prevent mineral deposits building up on the fronds. Hard-water marks can obscure the iridescent surface.

Avoid unnecessary rubbing or polishing of the foliage, particularly delicate new growth.

Feeding

Feed sparingly while the plant is actively growing. Use a weak, diluted fertiliser suitable for ferns or orchids, following the product’s guidance.

Avoid heavy feeding to accelerate growth. This is naturally a slow-growing plant, and additional fertiliser cannot replace suitable light, moisture and humidity.

Repotting

Repot when the rhizome and roots have outgrown the container or the growing medium has deteriorated. Choose a shallow container with drainage and only a little additional growing space.

Handle the rhizome and emerging fronds gently, retaining healthy roots wherever possible.

Common problems

• Brown, crisp edges: Check for drying compost, dry air or excessive light.

• Soft rhizomes or deteriorating roots: Investigate waterlogging and improve drainage.

• Greener foliage: Review light intensity; reduced blue sheen alone does not necessarily indicate poor health.

• Leaf loss after arrival: Some shedding can occur during acclimatisation. Maintain stable conditions and monitor the rhizome and new growth.

Propagation

Established plants can be propagated by carefully dividing the creeping rhizome. Keep healthy roots and a growing tip with each section, then maintain high humidity while the divisions establish.

Spore propagation is another option for experienced fern growers, although division is generally the more straightforward home method.

Seasonal care

During darker months, reduce watering and feeding if growth slows, while maintaining warmth and humidity. Continue checking the medium: lower water demand does not mean the fern should be allowed to dry out completely.