Why Are My Humata Fronds Curling?

Low humidity

Low humidity is the most common cause of humata frond curl in UK homes. The delicate, finely divided fronds of Humata tyermanii have relatively thin leaflet tissue that loses moisture readily in dry air. In centrally heated rooms in winter, UK homes can fall to 30 to 40 percent relative humidity, causing the frond leaflets to curl inward and the frond tips to brown. The white rhizomes on the surface of the potting mix also lose moisture in dry air, and they benefit from misting even on days when the potting mix is not watered.

What to do

• Position humata in a humid environment such as a bathroom or kitchen, or use a pebble tray with water beneath the pot to raise local humidity. As a small to medium fern, humata works well as a bathroom plant on a surface or shelf near natural light.
• Mist the foliage and rhizomes lightly with room-temperature water in dry conditions. This benefits both the fronds and the surface rhizomes, which absorb moisture from their scaled surface.
• In winter, keep humata away from radiators and heating vents. Even a small distance from a heat source makes a meaningful difference to the local humidity around the plant.

Underwatering

Underwatering causes humata fronds to curl progressively as the rhizomes and roots dry out. The finely divided fronds are relatively small in comparison to larger ferns, but their thin tissue loses moisture readily. When the epiphytic potting mix (orchid bark or similar) dries out completely, the fronds curl within a few days. Because humata is often grown in very free-draining substrates that dry faster than standard compost, it can dry out more quickly than gardeners expect, particularly in warm, well-lit positions in summer.

What to do

• Water humata when the top half of the potting mix is dry. In bark-based mixes, check by pressing a finger 2 to 3 centimetres into the substrate: if it feels dry at that depth, water thoroughly.
• Submerge the pot in a bowl of room-temperature water for 10 to 15 minutes every week or two to ensure the bark-based substrate is evenly moistened rather than just dampened on the surface.
• Mist the exposed rhizomes directly when watering, as they absorb moisture from their surface and help supply the plant during dry periods between waterings.

Overwatering

Overwatering in saturated potting mix causes the white rhizomes to rot. The rhizomes of humata are particularly susceptible because they sit on the surface of the potting mix and can be in direct contact with pooled water if the plant is over-irrigated. Rotted rhizome sections turn dark and slimy and lose their white, scaly appearance. Fronds attached to rotted rhizome sections yellow and die back rather than simply curling.

What to do

• Grow humata in a very fast-draining, bark-based potting mix rather than conventional houseplant compost. Coarse orchid bark with added perlite is ideal.
• Never let the pot sit in a pool of water. The surface rhizomes in direct contact with water at the base of the pot will rot quickly. Drain saucers promptly after watering.
• Reduce watering frequency in winter significantly. Cool temperatures and lower light levels slow growth and evaporation from the potting mix, making overwatering easy to cause by watering at a summer frequency.

Direct sun

Direct sun bleaches the delicate fronds of humata, causing the leaflets to curl and develop scorched, papery patches. Humata grows naturally in the shaded understorey of tropical forests, on the shaded sides of tree trunks and branches, and is not adapted to direct sun exposure. In UK homes, direct south- or west-facing sun in summer is too intense for humata fronds.

What to do

• Provide humata with bright, indirect light. A north- or east-facing windowsill, or a position 1 to 2 metres from a south-facing window, provides suitable light without direct sun exposure.
• Humata tolerates lower light levels than many houseplant ferns and can grow adequately in moderately shaded positions where other ferns might become too etiolated. However, very deep shade causes slow, weak growth and increases the risk of overwatering problems.

Cold temperatures

Humata is a tropical plant sensitive to cold. Temperatures below 10 degrees Celsius cause frond curl, yellowing, and deterioration. Cold windowsills in winter present a risk to the surface rhizomes, which are more exposed than the roots of terrestrial ferns and can be damaged by cold temperatures even when the air temperature is adequate. As a houseplant, humata requires frost-free, warm conditions year-round.

What to do

• Maintain humata above 13 to 15 degrees Celsius year-round. In most centrally heated UK homes this is achievable, but avoid cold hallways, unheated conservatories in winter, and cold windowsills where pot temperatures can drop well below ambient air temperature.
• In summer, humata can be moved outdoors to a warm, sheltered, shaded position where higher ambient humidity promotes vigorous rhizome extension and new frond production. Return indoors before autumn temperatures fall below 15 degrees Celsius.

Frequently asked questions

Why are my humata fronds curling?

Humata fronds curl most often from low humidity or underwatering. Humata tyermanii (white hare's foot fern) is an epiphytic fern from tropical Asia that grows on tree trunks and branches, where its creeping white rhizomes extend outward from the plant like legs radiating from a body. These rhizomes give the plant its common name and are one of its most distinctive features. The delicate, deeply divided fronds require consistent moisture and reasonable humidity to remain uncurled. In UK homes, central heating in winter is the most common cause of frond curl, driving ambient humidity below the level humata prefers.

How is humata different from davallia?

Humata and davallia (rabbit's foot fern) are closely related epiphytic ferns with similar creeping rhizomes and care requirements, and they are frequently confused. Both have distinctive, furry creeping rhizomes that extend across the surface of the potting mix and may drape over the edge of a hanging basket. The main differences are in the appearance of the rhizomes and the fronds: davallia rhizomes are typically brown or golden-brown and densely furry, resembling a rabbit's foot, while humata rhizomes are white or pale silver and longer, resembling a hare's foot or spider legs. The fronds of humata are also generally more finely divided and somewhat darker green than davallia.

Should I bury humata rhizomes?

The white, creeping rhizomes of humata should not be buried in potting mix. Like davallia, platycerium, and other epiphytic ferns, humata's rhizomes naturally grow on the surface of its substrate, and burying them in compost causes them to rot and prevents the plant from producing new fronds. When potting humata, set the rhizomes on the surface of the potting mix and allow them to extend outward across the surface and over the rim of the pot. The rhizomes can be misted directly when watering, as they absorb moisture from their surface. A shallow, wide container, a hanging basket with an open, airy substrate, or a bark mount are all suitable growing situations for humata.

What potting mix does humata need?

Humata grows best in a light, well-draining, epiphytic potting mix that provides good aeration around the rhizomes and roots. Coarse orchid bark mixed with perlite works very well. Standard houseplant compost is too dense and moisture-retentive for humata and will cause the rhizomes to rot if watered at a normal frequency. A substrate mix designed for epiphytic orchids or bromeliads is also suitable. The potting mix should be moist but never saturated, and should dry partially between waterings to maintain the aeration the rhizomes require.