Why Are My Pyrrosia Fronds Curling?

Drought stress

Pyrrosia is more drought-tolerant than most houseplant ferns, but the fronds will curl longitudinally when drought is prolonged. The felt covering of stellate hairs slows moisture loss considerably and can mask early drought stress, allowing the plant to appear healthy longer than more delicate ferns. However, once the fronds begin to curl, the plant has typically been dry for a significant period and the root system may be partially desiccated. The felt surface also makes it harder to judge moisture stress visually, so checking the potting mix or mount regularly is important rather than relying on frond appearance as the primary indicator.

What to do

• Check the potting mix or mounting moss regularly by touch: water a potted pyrrosia when the top half of the mix has dried, and a mounted pyrrosia when the moss pad feels barely damp rather than dry.
• Water thoroughly until water drains from the base of the pot. A mounted pyrrosia is best watered by soaking the moss pad in a bowl of room-temperature water for 15 to 20 minutes, then allowing it to drain before remounting.
• The grey-green colour of the felt surface is a useful indicator: in well-watered conditions the surface appears medium grey-green; as the plant dries out the felt tends to become paler and silvery as the hairs become more prominent against the desiccating frond tissue beneath.

Low humidity

Despite its drought-tolerant felt covering, pyrrosia still benefits from reasonable humidity and shows frond curl in very dry air. In centrally heated UK homes in winter, the ambient humidity can drop to 30 to 35 percent, which over time causes the fronds to curl at the margins and tips even in plants with an adequately moist root system. The curl is typically milder than in more sensitive ferns such as adiantum, reflecting pyrrosia's inherently greater resilience to dry air.

What to do

• Keep pyrrosia away from radiators and direct heating sources. A position a metre or more from the nearest heat source will significantly reduce the dry-air stress the plant experiences in winter.
• A pebble tray with water beneath the pot or mount provides continuous, gentle evaporative humidification of the local air around the plant. This is one of the simplest improvements for pyrrosia in a heated room.
• A naturally humid room such as a bathroom with good indirect light is an excellent position for pyrrosia: the ambient humidity from bathing and showering keeps conditions close to the plant's preferences without any additional equipment.

Overwatering

Overwatering is a more significant risk for pyrrosia than for most ferns that prefer consistently moist conditions. As an epiphyte adapted to free-draining, aerated substrates, pyrrosia's rhizome rots readily in persistently waterlogged potting mix. A waterlogged pyrrosia shows yellowing fronds that curl and soften, often with a sour smell from the potting mix. The root system collapses silently beneath the surface while the felt-covered fronds initially appear relatively healthy, which can delay diagnosis until significant damage has occurred.

What to do

• Use a very free-draining, bark-heavy potting mix: a combination of coarse orchid bark, perlite, and a small amount of peat-free compost provides adequate moisture retention while ensuring excellent drainage and aeration.
• Allow the potting mix to partially dry between waterings. Pyrrosia should never be kept in persistently moist conditions: the mix should cycle between moist and partly dry, never from wet to slightly dry.
• Ensure the pot has drainage holes and do not leave pyrrosia sitting in standing water in a saucer. Empty the saucer 20 to 30 minutes after each watering.
• If root rot is suspected, remove the plant from its pot, trim away any blackened rhizome or root sections, dust the cuts with powdered cinnamon or sulphur as a natural fungicide, and repot into fresh bark-based mix in a clean pot.

Direct sun

Although pyrrosia tolerates more light than most ferns and can grow in relatively bright, indirect positions, direct summer sun causes the felt surface to scorch and the fronds to curl and bleach. The felted covering provides some protection against light scorch compared to smooth-fronded ferns, but sustained direct sun through glass in summer is too intense even for pyrrosia. In its natural cliff-face and tree-trunk habitats, pyrrosia often grows in bright but dappled or intermittently shaded conditions rather than in continuous full sun.

What to do

• Provide bright, indirect light. A position near a north- or east-facing window, or filtered by a sheer curtain from a south- or west-facing window, suits pyrrosia well. In dim positions it grows slowly but remains healthy.
• On mounts or boards displayed on a wall, ensure the mounting position does not receive direct sun for extended periods. A wall in bright but indirect light is ideal for a mounted pyrrosia display.

Cold temperatures

Pyrrosia is variable in cold hardiness depending on species and origin. The commonly grown Pyrrosia lingua can tolerate brief frosts and is reportedly hardy in sheltered positions in mild UK gardens, particularly against a south-facing wall. However, most pyrrosia grown as houseplants perform best above 10 degrees Celsius. Cold draughts in winter cause localised frond curl on the side of the plant facing the cold source, even when overall temperatures are adequate.

What to do

• Keep most pyrrosia houseplants in temperatures above 10 degrees Celsius in winter, away from cold draughts and cold windowsills. The rhizome is more cold-sensitive than the fronds and must be kept warm.
• For trial plantings outdoors, choose sheltered south-facing positions against a warm wall in mild UK gardens. Cover with fleece during hard frosts and check for rhizome damage in spring: healthy rhizomes resume growth reliably once temperatures rise.

Frequently asked questions

Why are my pyrrosia fronds curling?

Pyrrosia fronds curl most often from drought stress or low humidity. Although pyrrosia is more drought-tolerant than most ferns, thanks to the dense felt of star-shaped hairs that covers its fronds and reduces moisture loss, extended dryness eventually causes the fronds to curl longitudinally and the felt covering to become more prominently visible as the frond tissue contracts. Low humidity accelerates moisture loss from the felt surface and causes the fronds to curl even when the root system is adequately watered, particularly in winter when central heating runs continuously.

What is pyrrosia and why do its fronds feel like felt?

Pyrrosia, commonly called tongue fern or felt fern, is an epiphytic fern native to Asia and Australasia that grows attached to trees, rocks, and cliffs in a wide range of habitats from tropical forests to rocky cliff faces. The dense covering of star-shaped (stellate) hairs on the frond surface gives pyrrosia its felt-like texture and grey-green colour. These hairs serve to reduce moisture loss from the frond surface, which is why pyrrosia is considerably more drought-tolerant than most ferns. The fronds of most species are simple (undivided), giving the plant a striking, strap-like or tongue-like appearance quite unlike conventional divided fern fronds.

How much water does pyrrosia need?

Pyrrosia requires less frequent watering than most houseplant ferns, as its felt covering reduces moisture loss and its epiphytic nature means it is adapted to periods of drying between rain events in its natural habitat. Water pyrrosia thoroughly when the top half of the potting mix has dried out, then allow it to partly dry again before the next watering. In winter, when growth is slow, watering every two to three weeks may be sufficient. However, do not allow the potting mix to remain completely dry for extended periods, as the felt covering can mask drought stress until significant damage has occurred.

Can pyrrosia be mounted on a board like a staghorn fern?

Yes, pyrrosia can be mounted on a piece of cork bark, driftwood, or a wooden board in a similar manner to platycerium (staghorn fern), as it is a natural epiphyte that grows attached to surfaces rather than in soil. Mount the rhizome on a damp pad of sphagnum moss held against the mounting surface with wire or fishing line, ensuring the rhizome has good contact with the moss. Water a mounted pyrrosia by soaking or misting the moss pad thoroughly and allowing it to dry partially between watering sessions. Mounted pyrrosia often grows more vigorously than pot-grown specimens and the creeping rhizome can be trained across the mounting surface to create an unusual wall or surface display.