Why Are My Todea Fronds Curling?

Drought

Drought is the most common cause of todea frond curl. The large, bipinnate fronds transpire significant quantities of moisture, and todea grows naturally at the margins of streams and in moist forest understorey where soil moisture is consistently high. When the soil or potting mix dries out, the fronds curl inward from the pinna margins, beginning at the frond tips and progressing toward the crown. In conservatory cultivation in summer, when temperatures are high and the plant is in full growth, water demand is substantial and the potting mix or container soil may dry out within days.

What to do

• Water todea thoroughly and consistently. In summer, check the potting mix every 3 to 4 days and water when the top 2 to 3 centimetres are dry. In winter, reduce watering but do not allow the potting mix to dry out completely.
• Water the fibrous crown of the plant as well as the potting mix, as todea absorbs moisture through the crown fibres as well as from the roots. In dry conditions, watering the crown directly provides a rapid moisture boost to the fronds above.
• In garden cultivation in mild areas, plant todea near a water source such as a pond edge or streambank where consistent soil moisture is naturally maintained.

Low humidity

Low humidity causes todea frond curl and browning at the pinna tips even when soil moisture is adequate. Todea grows naturally in moist forest environments with high ambient humidity, and the dry air of centrally heated UK homes and conservatories in winter is below what the plant prefers. The fronds curl from the pinna margins inward, and the tips of the fronds develop brown, dry patches in persistently low humidity.

What to do

• Position todea in the most humid available location: a warm conservatory with consistent moisture from the growing space, a cool greenhouse, or a bathroom with good natural light.
• Mist the fronds regularly with room-temperature water in dry conditions, particularly in winter when central heating reduces ambient humidity. For a large todea, a thorough misting of all frond surfaces is more beneficial than a quick spray.
• Use a pebble tray with water beneath the pot or container to provide continuous evaporative humidity around the plant.

Direct sun

Direct sun bleaches and scorches the large fronds of todea, causing the pinnae to curl and develop pale, papery patches. Todea grows naturally in shaded forest conditions and at streambanks where overhanging vegetation filters the light. In a conservatory in summer, direct sun through the glass is particularly damaging and can bleach the fronds rapidly.

What to do

• Provide todea with bright, indirect light in a conservatory. Apply shade cloth or use louvred blinds to filter direct sun in summer. In a garden position, plant todea in the shade of trees or a north-facing wall.
• Morning sun is less damaging than afternoon sun: a position receiving gentle morning light but shaded from noon onward is preferable to one receiving direct afternoon sun.

Frost

Todea barbara is not as cold-hardy as osmunda regalis and is susceptible to frost damage. Temperatures below about minus 3 to minus 5 degrees Celsius damage the fronds, and harder frosts can kill the plant. In most of the UK, todea must be kept frost-free in winter, either in a conservatory or cool greenhouse, or in very sheltered mild garden positions with adequate protection. The fibrous crown is somewhat more cold-tolerant than the fronds and may survive frost that kills the aerial growth, regenerating new fronds in spring.

What to do

• Keep todea in a frost-free conservatory or cool greenhouse in winter throughout most of the UK. A minimum winter temperature of 3 to 5 degrees Celsius is sufficient for most specimens, though warmer temperatures (above 8 degrees Celsius) promote better winter health and faster spring recovery.
• In the mildest UK gardens, protect the crown with a thick mulch of straw or dry bracken in autumn and wrap the fronds in several layers of horticultural fleece during forecast frost periods.

Wrong soil type

Todea grows best in moist, humus-rich, slightly acidic to neutral, well-draining soil. Like osmunda, it performs poorly in alkaline conditions and dislikes chalk and limestone substrates. In very free-draining, sandy, or poor soils, todea's moisture requirements cannot easily be met. In pots, a mix of peat-free compost, composted bark, and perlite provides suitable conditions.

What to do

• Amend planting soil generously with leaf mould or composted bark before planting todea in garden beds. The fibrous, humus-rich substrate of a forest streambank is the model: moisture-retentive but never waterlogged, with good structure and acidity.
• In pots, use a peat-free compost mixed with composted bark and perlite. Repot every 2 to 3 years as the fibrous crown expands, moving to a larger pot each time to accommodate the slow but steady growth of the crown.

Frequently asked questions

Why are my todea fronds curling?

Todea fronds curl most often from drought or low humidity. Todea barbara (king fern) is a large, impressive fern native to the moist forests and streambanks of Australia, New Zealand, and South Africa. Like its relative osmunda, todea produces very large, arching fronds from a dense fibrous crown, and in favourable conditions it eventually develops a substantial trunk. In UK conditions it is grown as a conservatory or very sheltered garden plant in the mildest areas. The large fronds transpire considerable moisture and curl inward from the pinna margins when soil moisture or ambient humidity is insufficient.

How is todea different from osmunda?

Todea and osmunda are closely related genera in the family Osmundaceae and share a similar overall appearance. Both produce large, arching fronds from a fibrous crown or short trunk, and both have spores borne directly on modified fertile fronds or frond sections. The main differences are: todea is native to the Southern Hemisphere (Australia, New Zealand, South Africa) while osmunda has a more worldwide distribution; todea barbara tends to be slightly less cold-hardy than osmunda regalis and is better suited to conservatory or sheltered garden cultivation in the UK; and todea fronds bear their spore cases (sporangia) directly on the normal pinnae (like leptopteris) rather than on distinctly modified fertile frond sections as osmunda does.

Is todea barbara hardy in the UK?

Todea barbara is not as hardy as osmunda regalis and is best treated as a conservatory or greenhouse plant in most of the UK. In the very mildest coastal gardens of Cornwall, South Devon, West Wales, and the west of Ireland, todea may survive outdoors in a sheltered position with some frost protection, but even in these areas it is not reliably hardy in colder winters. In a frost-free conservatory or cool greenhouse, todea grows well and over many years develops an impressive trunk that adds to its appeal as a specimen plant. It can be moved outdoors to a sheltered, shaded position in summer and returned indoors before autumn frosts.

Why is todea barbara called king fern?

Todea barbara is called king fern in its native range in Australia and New Zealand because of its large size, impressive stature, and the significant age that large specimens represent. Well-established plants with substantial trunks are known to be hundreds of years old in some cases, making todea one of the most long-lived of all fern species. In botanical gardens and specialist fern collections, large todea specimens with trunks of 30 to 50 centimetres or more are prized as historic living specimens. The 'king' designation reflects both the plant's impressive size and the respect accorded to very old specimens in Southern Hemisphere fern horticulture.