Why Are My Selaginella Leaves Curling?

Low humidity

Low humidity is the primary cause of leaf curl in decorative selaginella species grown as houseplants. The tiny, overlapping, scale-like leaves have very little moisture-storing capacity and respond almost immediately to air that is drier than their tolerance threshold, curling and crisping within a matter of hours in very dry conditions. Central heating in UK homes in winter is the most common cause of low-humidity damage, driving ambient humidity down to levels well below the 60 to 70 percent that most selaginella species require. Even brief periods of dry air, such as when a radiator runs overnight in a small room, can cause significant leaf curl.

What to do

• Grow selaginella in a terrarium or glass enclosure: the enclosed environment maintains the high, consistent humidity that selaginella thrives in and effectively eliminates low-humidity damage. A large, clear glass container with a partially closed top is the simplest and most reliable solution.
• In open rooms, position selaginella in naturally humid spaces such as bathrooms and kitchens, away from radiators and heating vents. A north-facing bathroom with indirect light is one of the most selaginella-compatible positions in a UK home.
• Use a room humidifier near selaginella in winter when central heating is running. Group selaginella with other moisture-loving plants to raise the collective humidity around the group through transpiration.

Underwatering

Underwatering causes selaginella leaves to curl, shrivel, and brown rapidly. The plant has very shallow roots and limited capacity to tolerate dryness, and the compost should remain consistently moist throughout. Even brief periods of dryness can cause disproportionate damage to the small, delicate leaves. In terrariums, selaginella rarely suffers from underwatering because the closed environment maintains moisture around the roots and foliage, but in open pots or border plantings it can dry out quickly, particularly in warm conditions.

What to do

• Keep the compost consistently moist but not waterlogged. Check the soil surface daily and water before the top centimetre dries out completely.
• Water selaginella with room-temperature water, avoiding cold tap water which can shock the roots of this warmth-loving plant.
• Outdoors, plant selaginella kraussiana as a groundcover in the moist, shaded positions it prefers: beneath large-leaved hostas or ferns, beside a water feature, or in a north-facing border with consistently moist soil. Once established in such conditions it requires little supplementary watering in the UK.

Direct sun

Direct sun bleaches and scorches selaginella foliage very quickly. The leaves lose their characteristic bright green or iridescent colouration, turning pale yellow-green before browning and crisping in prolonged direct light. Even a few hours of direct summer sun through glass can cause significant damage. Selaginella is a plant of forest floors and shadowed crevices, and bright indirect light or gentle dappled shade is the maximum light level it tolerates well.

What to do

• Keep selaginella out of direct sunlight. A position in bright, indirect light from a north- or east-facing window, or in the centre of a room away from any direct sun, is ideal indoors.
• For terrariums, avoid placing the glass container in direct sun as this rapidly overheats the interior and also causes direct light damage even to plants positioned away from the glass side that faces the sun.
• Outdoors, plant selaginella kraussiana only in deep or dappled shade. It is well-suited as a groundcover beneath established deciduous trees or large shrubs in reliably moist, shaded borders.

Cold temperatures

Most decorative selaginella species are tropical in origin and sensitive to cold. Temperatures below 10 degrees Celsius cause leaf curl and browning in tropical species such as Selaginella uncinata and Selaginella martensii. Cold draughts from poorly sealed windows in winter are a common cause of sudden leaf curl in selaginella placed near window sills. The outdoor species Selaginella kraussiana is somewhat hardier, tolerating light frost in sheltered positions in mild UK gardens, but it is not fully reliable below minus 5 degrees Celsius and requires protection in colder areas.

What to do

• Keep tropical selaginella species in rooms that maintain a minimum temperature of 12 to 15 degrees Celsius. Move plants away from cold windows in winter and keep them clear of exterior walls that become cold at night.
• In terrariums, the enclosed glass provides some insulation against ambient cold, but avoid placing glass terrariums on cold windowsills in winter where the base of the container may be significantly colder than the room air temperature.
• For outdoor Selaginella kraussiana in cold UK areas, apply a light mulch of leafmould over the planting area in autumn to provide some frost insulation for the shallow root system.

Overwatering

Overwatering causes selaginella stems to rot at the base, turning black and slimy, which then prevents the rest of the plant from receiving water and causes the upper leaves to curl and yellow. This is most common in terrariums with poor drainage or in pots without drainage holes. Selaginella needs consistent moisture but not permanently saturated conditions: the roots require some air in the substrate to remain healthy.

What to do

• Ensure terrariums have a drainage layer of gravel or perlite beneath the substrate layer to prevent water from pooling at root level. Even in a closed terrarium, a drainage layer of at least 2 to 3 cm prevents root rot in a well-planted container.
• For potted selaginella, use a substrate that retains moisture but also drains freely: a mix of peat-free compost and perlite or coarse sand, or a purpose-made terrarium substrate, is suitable.
• If stem rot is detected, cut away the affected stems cleanly with scissors, allow the soil surface to dry slightly, and reduce watering frequency. Healthy stems can be propagated by pressing them into fresh, moist compost to root.

Frequently asked questions

Why are my selaginella leaves curling?

Selaginella leaves curl most often from low humidity or underwatering. Selaginella is a moisture-loving plant from tropical and subtropical environments and is particularly intolerant of dry air. In UK homes, central heating in winter rapidly lowers ambient humidity to levels that cause the tiny, scale-like leaves to curl, brown, and crisp. The plant can desiccate very quickly in dry conditions because the leaves have very little capacity to store moisture and respond almost immediately to humidity falling below their threshold.

Is selaginella a moss?

Selaginella is not a true moss but a spike moss, a member of an ancient group of plants called lycophytes. It superficially resembles moss in its small, scale-like, densely packed leaves and creeping or mounding growth habit, and it is often described as moss-like in appearance. However, it is a vascular plant with a more complex internal structure than true mosses, and it has different care requirements: it prefers slightly more light than most mosses and benefits from a well-draining substrate rather than the constantly saturated conditions some mosses prefer.

Why is my selaginella turning brown?

Selaginella turns brown most often from low humidity, underwatering, or direct sun exposure. In dry, heated rooms the small leaves crisp and brown rapidly. Some selaginella species, particularly Selaginella lepidophylla (the resurrection plant), are adapted to curl into a brown dormant ball when completely dry and then revive and unfurl when rewetted, but this is a survival mechanism and should not be regarded as a normal growing condition. For decorative selaginella species grown as houseplants, brown crispy foliage indicates stress that should be addressed promptly.

What is the best way to grow selaginella indoors?

Selaginella grows best indoors in high-humidity environments such as terrariums, glass enclosures, or humid bathrooms. It is one of the most popular plants for closed and open terrariums because it thrives in the consistently high humidity of an enclosed glass container. In open rooms, it performs best in naturally humid spaces away from central heating. Bright, indirect light with consistently moist but not waterlogged soil, and humidity above 60 percent, will keep most decorative selaginella species in excellent condition.