Why Are My Lygodium Leaves Curling?

Low humidity

Low humidity is the most common cause of lygodium leaf curl in UK indoor cultivation. The delicate, thin-textured pinnae lose moisture rapidly to dry air and curl and crisp within days when ambient humidity drops below their threshold. Central heating in winter is the primary cause: heated rooms in UK homes in winter can fall to 30 to 35 percent relative humidity, while lygodium requires at least 50 to 60 percent for healthy growth. The problem is compounded by the plant's active climbing growth, which produces continuous new pinnae that are particularly vulnerable when they first emerge.

What to do

• Position lygodium in a conservatory, humid greenhouse, or bathroom where ambient humidity is consistently higher than in heated living rooms. A warm, bright, humid conservatory with a water feature or other source of ambient moisture provides close to ideal conditions.
• Use a room humidifier near the plant in winter. A pebble tray with water beneath the pot also helps raise local humidity continuously through evaporation.
• Keep lygodium away from radiators and heating vents. Position it away from draughty windows and exterior doors that allow cold, dry air to flow over the foliage in winter.
• Mist the pinnae lightly in summer with room-temperature water when the air is very dry, but avoid misting in cold conditions or in rooms with poor air circulation.

Underwatering

Underwatering causes the pinnae of lygodium to curl inward and brown at the margins before the entire pinna dries and falls from the rachis. As a fast-growing, actively climbing plant when conditions are suitable, lygodium has higher water requirements per unit of growth than slower-growing, compact ferns. The potting mix should remain consistently moist throughout the growing season. In warm, well-lit conservatories in summer, lygodium may need watering twice a week or more to keep pace with its growth rate.

What to do

• Water lygodium regularly, keeping the potting mix consistently moist but not waterlogged. Check the mix every two to three days in warm growing conditions and water before the top 2 centimetres dry out.
• In winter when growth slows, reduce watering frequency but continue to check and water when needed. Do not allow the potting mix to dry out completely between waterings even in winter.
• Water thoroughly each time, ensuring the entire root ball is moistened. Allow excess water to drain from the pot and empty the saucer after 30 minutes.

Cold temperatures

Lygodium is sensitive to cold and growth stops, and the pinnae curl and yellow, when temperatures fall below around 10 degrees Celsius. In temperatures below 5 degrees Celsius the plant may be killed outright if the cold is prolonged. In UK conditions, lygodium must be kept in heated rooms or a frost-free conservatory throughout winter. Cold draughts from windows and doors cause localised pinna curl even when the overall room temperature is adequate, as the cold, moving air chills the fronds directly.

What to do

• Keep lygodium at a minimum temperature of 10 to 12 degrees Celsius year-round. A heated conservatory or warm greenhouse is an excellent year-round environment, allowing continuous active growth in winter as well as summer.
• Move lygodium away from cold windows in winter. Do not place the pot on a cold windowsill where the root ball may be chilled even if the air temperature above is adequate.
• In summer, lygodium can be moved outdoors to a sheltered, warm, humid position, which promotes vigorous climbing growth. Return it indoors before autumn temperatures drop.

Direct sun or deep shade

Lygodium requires bright, indirect light for vigorous growth and performs poorly in either extreme. Direct summer sun through glass scorches the delicate pinnae, causing them to bleach, curl, and drop. Deep shade causes growth to slow dramatically and the pinnae to pale and weaken. Bright, indirect light from a large, shaded south- or east-facing window, or the dappled light of a lightly shaded conservatory, is ideal for sustained growth and healthy foliage.

What to do

• Provide bright, indirect light throughout the growing season. In a conservatory, shade the glass in summer with blinds or shade paint to prevent direct sun from scorching the pinnae while maintaining high ambient light levels.
• Outdoors in summer, grow lygodium in a position with morning sun and afternoon shade, or in dappled light beneath a pergola or open-canopy tree. Direct afternoon sun should be avoided.
• In winter, maximise light: move the plant to the brightest available position to sustain photosynthesis and maintain minimum viable growth. Lack of light in winter reduces plant resilience and makes it more susceptible to other stress factors.

Overwatering

Overwatering in persistently saturated potting mix causes lygodium roots to rot. The damaged root system cannot supply water to the climbing fronds, causing them to yellow and curl despite the compost remaining wet. Overwatered lygodium typically shows yellowing and softening of the pinnae rather than the crisping associated with drought, and the potting mix may develop a sour odour.

What to do

• Use a free-draining potting mix with added perlite to prevent waterlogging. A mix of peat-free compost and 25 to 30 percent perlite drains well while retaining adequate moisture for active growth.
• Ensure the pot has drainage holes and never leave lygodium sitting in standing water in a saucer for extended periods.
• If root rot is suspected, remove the plant from its pot, trim away any blackened root material, allow the remaining root system to dry briefly, and repot into fresh, well-draining compost in a clean pot.

Frequently asked questions

Why are my lygodium leaves curling?

Lygodium leaves curl most often from low humidity or underwatering. Lygodium japonicum (Japanese climbing fern) and related species are plants of humid subtropical and tropical forests where moisture levels are consistently high and temperatures warm. In UK indoor cultivation, central heating in winter creates very dry air that causes the delicate, climbing frond segments to curl and crisp. Underwatering causes a similar response, and because lygodium is an active, fast-growing climber when conditions are suitable, it requires consistent moisture to sustain its growth.

Is lygodium a true fern?

Lygodium is a true fern, though its growth habit is quite unlike that of most ferns. Rather than producing fronds from a central crown or creeping rhizome, lygodium produces long, twining fronds that climb by winding around supporting structures, reaching several metres in length under ideal conditions. It is the only group of ferns with a genuinely climbing habit. The individual leaflets (pinnae) along the twining rachis are the photosynthetically active parts of the frond, and it is these that curl when the plant is stressed. Lygodium japonicum (Japanese climbing fern) is the species most commonly grown in the UK as a houseplant or conservatory plant.

Can lygodium be grown outdoors in the UK?

Lygodium is a frost-tender tropical or subtropical plant and cannot be grown outdoors year-round in the UK. It requires frost-free conditions throughout winter and performs best as a houseplant or conservatory plant where temperatures remain above 10 degrees Celsius at all times. In summer, a sheltered, warm, humid position outdoors is suitable and can promote vigorous climbing growth, but the plant must be moved back inside before the first autumn frosts. In mild conservatories and heated greenhouses, lygodium can remain active year-round and develop impressive climbing displays.

How do I support lygodium as a climbing plant?

Lygodium climbs by twining its frond rachis around thin supports, performing best on fine wire, string, or thin bamboo canes that the winding rachis can grip and coil around effectively. Thick, wide supports that the rachis cannot wrap around do not work well. A trellis of fine wire or twine stretched between upright supports provides an ideal climbing frame. In conservatories and large rooms, lygodium can be trained up and along wire stretched between hooks on walls or ceilings to create an unusual, fern-covered green screen effect.