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delta maidenhair (Adiantum raddianum)

Adiantum raddianum is a perennial herbaceous fern that may grow terrestrially or on rock, with a short, creeping, branching rhizome and a clumping habit.

LightSources differ somewhat, but bright indirect light to partial shade is described as most suitable; it can tolerate shadier positions, although excessive shade can reduce vigor, and sudden exposure to strong direct sunlig
WaterKeep the growing medium evenly moist but well drained, without allowing the roots or medium to dry out completely; provide more water from spring through autumn, wait until the surface begins to dry before watering in wi
HumidityAdiantum raddianum prefers high humidity and needs moderate airflow.
TemperatureA minimum of about 5 °C is reported, but this figure comes from few sources. It is generally reported for a warm hardiness zone, although the available zone information comes from a single source. It is tender.
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delta maidenhair illustration

Overview

Adiantum raddianum is a perennial herbaceous fern that may grow terrestrially or on rock, with a short, creeping, branching rhizome and a clumping habit.

Origin and habitat

Sources differ on its native range, describing it as native to tropical America, including South America and the West Indies. It is associated mainly with tropical American environments and favors warm, humid, shaded conditions; in temperate regions it is commonly grown indoors or in greenhouses.

Characteristics

Mature spread is 30–60 cm. Sources differ in their descriptions of the fronds, which range from triangular to elongated triangular or ovate-lanceolate, are divided into multiple pinnate divisions, and have fan-shaped to wedge-shaped pinnules with lobed or finely toothed margins. The slender stipes and rachises are dark to black and glossy; young fronds may be more upright, while mature fronds often arch downward. It has a creeping rhizome.

Light

Sources differ somewhat, but bright indirect light to partial shade is described as most suitable; it can tolerate shadier positions, although excessive shade can reduce vigor, and sudden exposure to strong direct sunlight should generally be avoided.

Watering

Keep the growing medium evenly moist but well drained, without allowing the roots or medium to dry out completely; provide more water from spring through autumn, wait until the surface begins to dry before watering in winter, and avoid prolonged waterlogging.

Humidity and airflow

Adiantum raddianum prefers high humidity and needs moderate airflow.

Temperature and dormancy

A minimum of about 5 °C is reported, but this figure comes from few sources. It is generally reported for a warm hardiness zone, although the available zone information comes from a single source. It is tender.

Growing medium and mounting

Use a humus-rich, moist but well-drained medium; sources support either loam or a general indoor-plant potting medium, with neutral to slightly alkaline conditions preferred.

Feeding

During the growing season, regular light feeding is supported, with sources describing diluted general liquid fertilizer as well as slow-release or liquid feeding schedules.

Propagation

Propagation can be by division or by sowing spores; sources recommend sowing mature spores promptly and describe rhizome division at suitable times that differ between sources. Spores are borne beneath reflexed lobes along the frond margins and are reported to be suitable for sowing once mature.

Common problems

Sources differ on pest problems, reporting scale insects, mealybugs, Florida fern caterpillar, and slugs that may damage tender fronds. Sources mention damping-off or wilt-type diseases and overly wet conditions as a possible factor, while another source reports no significant disease problems in general. Dry growing medium can impair growth, strong light may scorch the fronds, and sudden environmental changes may damage them. It does not tolerate low temperatures well; in temperate regions it is advised to be moved indoors during winter and kept away from direct heating or cooling airflow.

Identification

It is reported to have slender, glossy black stipes and rachises and fan-shaped to triangular pinnules, with sori along the frond margins covered by false indusia formed from the reflexed margins.

Photos

Adiantum raddianum
📷 Forest & Kim Starr · CC BY 3.0 · source
Adiantum raddianum
📷 no rights reserved, uploaded by Peter de Lange · CC0 · source
Adiantum raddianum
📷 Vítor Jorge, some rights reserved (CC BY), uploaded by Vítor · CC BY · source

Sources