Why Are My Phlebodium Fronds Curling?

Underwatering

Underwatering is the most common cause of phlebodium frond curl. The large, lobed fronds have considerable surface area and lose moisture to the surrounding air continuously, requiring the rhizome and roots to supply a steady stream of water. When the potting mix dries out, the fronds curl inward along their length within a few days, and the distinctive blue-green colour may appear duller and less vibrant than in a well-watered plant. Because phlebodium is often grown in bark-based, epiphytic mixes that drain faster than conventional compost, it can dry out more quickly than gardeners used to soil-based houseplants expect.

What to do

• Water phlebodium when the top half of the potting mix has dried out. In bark-based mixes this may mean watering every 5 to 7 days in warm conditions and every 10 to 14 days in winter.
• Water thoroughly, ensuring the entire potting mix is moistened. Alternatively, soak the pot in a bowl of room-temperature water for 15 to 20 minutes then allow to drain fully, which ensures the bark-based mix is evenly moistened rather than just the surface.
• Mist the orange surface rhizomes directly when watering, as they absorb moisture from their surface as well as from the potting mix.
• After rewetting a drought-stressed plant, curled fronds typically begin to unfurl within 24 to 48 hours if the moisture stress was caught early. Badly desiccated fronds can be cut back to allow new growth to emerge.

Low humidity

Low humidity causes phlebodium fronds to curl at the lobes and tips even when the root system is adequately moist. The waxy surface coating that gives the fronds their blue colour provides some protection against moisture loss, making phlebodium more humidity-tolerant than adiantum or selaginella, but central heating in winter still drives ambient humidity below the level phlebodium prefers. The frond tips are the first areas to show low-humidity damage, curling and developing dry, brown margins before the rest of the frond is affected.

What to do

• Position phlebodium in a naturally humid room such as a bathroom or kitchen, or use a pebble tray with water beneath the pot to raise local humidity through continuous evaporation.
• Keep phlebodium away from radiators and heating vents. Its tolerance of lower light means it can be positioned further from windows and thus further from the cold draughts and warm, dry air that often coexist near windows in winter.
• A room humidifier near the plant in winter is the most effective solution for homes with persistent low-humidity issues from central heating.

Direct sun

Direct sunlight bleaches the distinctive blue-green fronds of phlebodium, removing the waxy surface coating that produces the blue colour and causing the fronds to turn a pale, washed-out yellow-green. The fronds also curl and develop scorched patches. Once bleached, the blue colouration does not return to the damaged fronds, though new fronds grown in correct light conditions will emerge with the characteristic blue-green colour. This colour loss makes phlebodium particularly sensitive to position relative to sun exposure.

What to do

• Position phlebodium in indirect or filtered light. A north-facing windowsill, a position in the interior of a room with large windows, or a spot behind a sheer curtain from a south- or west-facing window all work well.
• Phlebodium is one of the few houseplant ferns genuinely well-suited to low-light positions such as north-facing rooms, bathrooms without direct window access, or office environments with artificial lighting. Its blue-green fronds also show particularly well in lower light conditions where conventional green foliage plants appear dull.

Overwatering

Overwatering in persistently saturated potting mix causes the orange rhizomes and roots of phlebodium to rot. The fronds of an overwatered phlebodium yellow rather than curl and brown, and sections of the surface rhizome become dark and slimy. As an epiphyte adapted to growing on surfaces with excellent aeration around its roots, phlebodium is more susceptible to overwatering than ferns adapted to consistently moist soil conditions.

What to do

• Use a bark-based, well-draining potting mix rather than conventional houseplant compost. Coarse orchid bark mixed with perlite is excellent for phlebodium, providing good moisture retention with the aeration the rhizomes need.
• Never leave phlebodium sitting in water in a saucer for extended periods. The surface rhizomes in direct contact with standing water deteriorate quickly.
• Reduce watering frequency in winter significantly: the plant's growth slows, temperatures are lower, and the potting mix dries more slowly, making overwatering much easier to cause.

Cold temperatures

Phlebodium is a tropical and subtropical plant and is sensitive to cold. Temperatures below 10 degrees Celsius cause the fronds to curl, yellow, and deteriorate. Cold draughts from windows in winter cause localised damage to the fronds nearest the cold source. The rhizomes are particularly cold-sensitive and can be damaged by cold windowsills even when the air temperature in the room is adequate.

What to do

• Maintain phlebodium in temperatures above 12 to 15 degrees Celsius year-round. Avoid cold windowsills in winter and keep the plant away from draughty exterior doors and windows.
• In summer, phlebodium can be moved outdoors to a sheltered, shaded, warm position, which promotes vigorous rhizome extension and frond production. Return it indoors before autumn temperatures drop below 15 degrees Celsius.

Frequently asked questions

Why are my phlebodium fronds curling?

Phlebodium fronds curl most often from underwatering or low humidity. Phlebodium aureum (blue star fern) is an epiphytic fern that grows naturally on tree trunks and rocky surfaces in tropical and subtropical America, where it experiences irregular rainfall and periods of dryness. Despite this epiphytic adaptation, the large, lobed fronds with their distinctive blue-green colour lose moisture readily and curl inward when the rhizome dries out or when ambient humidity falls below the plant's preferred range. Central heating in UK homes in winter is a significant cause of frond curl for indoor phlebodium.

Why is phlebodium called blue star fern?

Phlebodium aureum is commonly called blue star fern because of the distinctive blue-green or blue-grey colour of its large, lobed fronds, which is unusual among houseplant ferns and gives the plant a striking appearance quite different from the typical mid-green of most ferns. The 'star' element of the common name refers to the star-shaped pattern of the deeply lobed frond outline. The blue colouration comes from a waxy coating on the frond surface that reflects light at blue wavelengths, similar to the bloom on certain varieties of grape or cabbage. This waxy surface also provides some protection against moisture loss.

Should I bury the rhizomes of my phlebodium?

The orange-coloured, creeping rhizomes of phlebodium should not be buried in potting mix. Like davallia and microsorum, phlebodium is an epiphyte whose rhizomes naturally grow on the surface of its substrate, and burying them can cause them to rot. When repotting phlebodium, set the rhizomes on the surface of the potting mix, anchoring them lightly if needed. The rhizomes will extend across the surface and may eventually creep over the edges of the pot. They can be misted directly, as they absorb moisture from their surface as well as from the potting mix beneath them.

How much light does phlebodium need?

Phlebodium tolerates a wider range of light conditions than most houseplant ferns and is particularly valued for its ability to grow in low-light positions where other ferns would struggle. It grows well in bright, indirect light but can also perform adequately in moderate shade. Direct sun causes bleaching and scorching of the distinctive blue-green fronds, removing the blue colouration and damaging the waxy surface coating that gives the fronds their characteristic appearance. A position away from direct sun in a reasonably lit room, or close to a north-facing window, suits phlebodium well.