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Boston swordfern (Nephrolepis exaltata)

Nephrolepis exaltata is an evergreen perennial fern that may grow terrestrially or as an epiphyte, has rhizomes, can form runners, and commonly develops a clumping habit.

LightBright indirect light is preferred indoors, while partial shade to shade is suitable outdoors; strong direct sunlight should be avoided.
WaterKeep evenly moist in a well-drained growing medium and avoid waterlogging; indoors, the medium should not be allowed to dry completely, while watering should be reduced in winter.
HumidityNephrolepis exaltata has a high humidity need.
TemperatureA single source reports a minimum temperature of about 5 °C, so sources are few. It is generally reported for a warm hardiness range and is tender.
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Boston swordfern illustration

Overview

Nephrolepis exaltata is an evergreen perennial fern that may grow terrestrially or as an epiphyte, has rhizomes, can form runners, and commonly develops a clumping habit.

Origin and habitat

Nephrolepis exaltata is primarily native to tropical and subtropical parts of the Americas, including Florida, Mexico, Central America, the Caribbean, and South America, while sources differ over whether Hawaii, Africa, Asia, or Polynesia are also part of its native or natural distribution. It favors moist, shaded conditions and occurs in moist forests, swamps, and floodplains; it can grow terrestrially or as an epiphyte and less commonly on rocks. It is mainly associated with tropical to subtropical, humid environments.

Characteristics

Sources differ, with the limited evidence placing mature height at about 50–100 cm. A single source reports a mature spread of about 100–150 cm, so sources are few. The pinnate fronds are linear to lanceolate or oblanceolate overall, with narrow elongated pinnae, and may be upright or arching; frond dimensions vary markedly among sources and cultivated forms. It is reported to have an erect rhizome.

Light

Bright indirect light is preferred indoors, while partial shade to shade is suitable outdoors; strong direct sunlight should be avoided.

Watering

Keep evenly moist in a well-drained growing medium and avoid waterlogging; indoors, the medium should not be allowed to dry completely, while watering should be reduced in winter.

Humidity and airflow

Nephrolepis exaltata has a high humidity need.

Temperature and dormancy

A single source reports a minimum temperature of about 5 °C, so sources are few. It is generally reported for a warm hardiness range and is tender.

Growing medium and mounting

The growing medium should be moist, well drained, nutrient-rich, and acidic to neutral, with loamy or sandy substrates suitable. For indoor cultivation, RHS also recommends a peat-free multipurpose medium or a mixture of loam, coarse sand, and leaf mould.

Feeding

During the growing season, a balanced liquid fertilizer at reduced strength may be applied regularly; another source places the suitable feeding period from early summer through summer.

Propagation

Propagation can be by division or by separating rooted runners or offsets; the species can also be propagated from spores, although named cultivated forms should not be assumed to retain their characteristics from spores. Spores can form on the undersides of the fronds, although some cultivated forms may not produce spores. Division is suitable during a warmer part of the growing season, according to the reported timing.

Common problems

Potential pests include scale insects, spider mites, and Florida fern caterpillar. Excessive winter watering can cause root rot, and fronds that remain wet for prolonged periods may also rot. It is generally reported to be intolerant of frost; after frost the above-ground growth may appear completely dead, but in suitable outdoor hardiness areas it may regrow in spring.

Identification

The pinnate fronds taper toward the tip, while the pinnae have auriculate, asymmetrical bases and round sori positioned near the veins. Sources differ, and some also distinguish it from similar species by the absence of root tubers.

Photos

Nephrolepis exaltata
📷 unknown · CC BY-SA 3.0 · source
Nephrolepis exaltata
📷 Thomas Irvine, some rights reserved (CC BY), uploaded by Tho · CC BY · source

Sources