Why Are My Rumohra Fronds Curling?

Drought stress

Rumohra is more drought-tolerant than many houseplant ferns, and its leathery fronds can withstand brief periods of dryness without the rapid collapse seen in adiantum or selaginella. However, prolonged drought causes the fronds to curl inward along the rachis and the pinnule margins to brown progressively from the tips. In conservatories in summer, the combination of high temperatures and fast evaporation from bark-based mixes can cause rumohra to dry out faster than expected, and frond curl can develop within a week or two of insufficient watering. Cut fronds displayed in floral arrangements also curl rapidly when the stipe ends are not in water.

What to do

• Water rumohra when the top 3 to 4 centimetres of potting mix feel dry. Because rumohra tolerates some dryness, it can be allowed to dry slightly more between waterings than adiantum or selaginella, but should not be left bone dry for extended periods.
• In hot conservatories in summer, check the potting mix every two to three days. High temperatures and strong light dramatically increase the rate of water loss from both the potting mix and the fronds.
• Apply a bark or leafmould mulch around the base of rumohra in outdoor plantings to reduce soil moisture loss and keep the root zone cool in warm weather.

Direct sun

Direct sunlight causes rumohra fronds to bleach and curl even though the leathery texture provides more protection than delicate fern fronds. In its natural habitats across southern hemisphere forests, rumohra typically grows in shaded or dappled conditions beneath tree canopy. In conservatories, the combination of direct summer sun through glass and high temperatures creates conditions that are too intense even for this relatively tough fern, causing frond bleaching, curl, and tip burn.

What to do

• Shade conservatory glass with blinds or shade paint in summer to filter direct sun. Rumohra grows well in the bright, indirect light of a shaded conservatory and does not require direct sun to thrive.
• Outdoors in mild UK gardens, plant rumohra in partial shade beneath trees or beside north-facing walls. Morning sun with afternoon shade is acceptable; full afternoon sun should be avoided.
• As a houseplant, position rumohra in bright, indirect light away from direct sun. It tolerates lower light levels than many ferns and can perform reasonably in the middle of a bright room.

Low humidity

Although rumohra's leathery fronds are more resistant to low humidity than the delicate fronds of adiantum or davallia, extended exposure to very dry, heated air in winter causes the pinnule margins to curl and brown. In the centrally heated UK homes where rumohra is increasingly grown as a houseplant rather than solely as a conservatory plant, winter humidity can fall well below the 50 percent level that suits it best.

What to do

• Keep rumohra away from radiators and underfloor heating vents, which dramatically reduce local humidity. A pebble tray with water beneath the pot provides gentle, continuous humidification without any additional equipment.
• In conservatories, a water feature or humidifier maintains higher ambient humidity and benefits all the plants growing in the space simultaneously.
• As one of the more humidity-tolerant of commonly grown houseplant ferns, rumohra is a good choice for positions in the home where conditions are not ideal for more demanding ferns.

Cold and frost

Rumohra is frost-tender and cannot survive temperatures below about minus 3 degrees Celsius. Cold causes the leathery fronds to curl inward, then turn a yellowish brown before dying back. The rhizome may survive light frosts even when the fronds are killed, and regenerate new growth in spring, but hard or prolonged frost kills the plant entirely. In the UK, rumohra should be considered a frost-free conservatory or greenhouse plant except in the very mildest coastal gardens.

What to do

• Maintain rumohra in temperatures above 5 degrees Celsius at all times, with better performance above 10 degrees. In a frost-free conservatory, minimal winter watering and temperatures above freezing are sufficient to keep the plant alive through winter.
• For outdoor plantings in mild UK gardens, provide frost protection with horticultural fleece over the crown when frost is forecast, or mulch the base heavily with dry bracken or straw to protect the rhizome from frost penetration.
• In cold-snaps, prioritise protecting the rhizome rather than the fronds: a frond-killed plant with a living rhizome will regrow in spring, but a rhizome-killed plant will not.

Overwatering

Overwatering in persistently wet conditions causes rumohra roots and rhizome to rot. The tough fronds mask early signs of root rot: the plant may appear healthy for some time before the fronds begin to yellow, curl, and droop. In winter, when growth is slow and water evaporates more slowly from the potting mix, overwatering is particularly easy to cause by continuing to water at the same frequency as in summer.

What to do

• Reduce watering significantly in winter, checking the potting mix before each watering rather than following a fixed schedule. In cool conservatories in winter, rumohra may need watering only every two to three weeks.
• Ensure pots have drainage holes and use a well-draining potting mix. A bark-based mix with added perlite drains well and reduces the risk of waterlogging.
• For commercial cut-foliage production, rumohra is typically grown in raised beds with excellent drainage and regular but not excessive watering, which achieves consistent frond quality without the root problems associated with overwatered pot-grown plants.

Frequently asked questions

Why are my rumohra fronds curling?

Rumohra fronds curl most often from drought stress or direct sun exposure. Rumohra adiantiformis (leatherleaf fern) is more drought-tolerant than many houseplant ferns, thanks to its tough, leathery frond texture, but the fronds will curl inward and the pinnule margins will brown when the plant goes without water for too long or is placed in bright direct sun. The plant is popular as a cut foliage fern used by florists and as a conservatory or mild-garden plant, and both uses put it in conditions that can lead to moisture stress if care is not maintained.

Is rumohra the same as leatherleaf fern?

Yes, Rumohra adiantiformis is the species commonly known as leatherleaf fern, and it is the same fern widely used by florists as cut foliage in flower arrangements. Its tough, long-lasting, dark green fronds with finely textured pinnules remain fresh for an unusually long time after cutting, making it one of the most commercially important foliage ferns in the floristry trade. In the UK it is grown commercially under glass and also planted outdoors in very mild gardens. As a houseplant it is less commonly grown than some other ornamental ferns but is a resilient choice for conservatories and cool, bright rooms.

Can rumohra be grown outdoors in the UK?

Rumohra adiantiformis can be grown outdoors in the mildest parts of the UK, particularly in the Isles of Scilly, the Channel Islands, coastal Cornwall and Devon, and other areas with very mild winters where frosts are rare or very light. In these areas it grows as an evergreen, spreading ground-cover or border plant in sheltered, lightly shaded positions. In the rest of the UK it is better grown in a frost-free greenhouse or conservatory, or as a houseplant, as temperatures below about minus 3 degrees Celsius damage the fronds and hard frosts will kill the plant.

How do I use rumohra as a cut foliage fern?

Rumohra fronds last exceptionally well as cut foliage when cut correctly and conditioned properly. Cut fronds early in the morning when the plant is well hydrated, using clean, sharp scissors or secateurs. Recut the stipe ends at a 45-degree angle under water to prevent air blocks in the vascular tissue, then place immediately in clean water with a small amount of cut flower food. Rumohra fronds typically last 10 to 14 days in water when kept in a cool room away from direct sun and heating vents. Replace the water every two to three days and recut the stipe bases to prolong vase life.