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Boston swordfern (Nephrolepis exaltata)

Nephrolepis exaltata is an evergreen, rhizomatous, perennial herbaceous fern that may be terrestrial or epiphytic, commonly forming clumps, with some plants producing stolons. It is generally described as terrestrial.

LightBright indirect light is best for indoor cultivation; outdoors, partial shade to shade is preferred, with strong direct sunlight avoided.
WaterDuring growth, keep evenly moist without waterlogging and do not allow the soil to dry out completely; reduce watering in winter, as excessive moisture may cause root or frond rot.
HumidityIt is generally reported to have a high humidity need.
TemperatureA single source reports a minimum temperature of about 5 °C. Sources differ on the ideal temperature, placing it at about 15–25 °C. It is generally reported in a USDA hardiness zone and is tender.
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Boston swordfern illustration

Overview

Nephrolepis exaltata is an evergreen, rhizomatous, perennial herbaceous fern that may be terrestrial or epiphytic, commonly forming clumps, with some plants producing stolons. It is generally described as terrestrial.

Origin and habitat

It is mainly native to tropical and subtropical parts of the Americas, including Florida, Mexico, Central America, the Caribbean, and South America; sources differ, with some also including Hawaii, Polynesia, and Africa in its natural or native range. It favors moist, shaded habitats and occurs in wetlands, swamps, and floodplains; it may grow terrestrially or epiphytically and less often on rocks, from low to middle elevations. Its climate is tropical to subtropical, warm, and humid.

Characteristics

Sources differ on mature height, placing it at about 40–100 cm. A single source reports a mature spread of about 100–150 cm. The pinnately compound fronds are narrow and linear to lanceolate, usually taper toward the tip, have narrow pinnae and round sori on their undersides, and may arch and droop in cultivated forms.

Light

Bright indirect light is best for indoor cultivation; outdoors, partial shade to shade is preferred, with strong direct sunlight avoided.

Watering

During growth, keep evenly moist without waterlogging and do not allow the soil to dry out completely; reduce watering in winter, as excessive moisture may cause root or frond rot.

Humidity and airflow

It is generally reported to have a high humidity need.

Temperature and dormancy

A single source reports a minimum temperature of about 5 °C. Sources differ on the ideal temperature, placing it at about 15–25 °C. It is generally reported in a USDA hardiness zone and is tender.

Growing medium and mounting

Use a moist but well-drained, relatively nutrient-rich medium, such as loam or a sandy substrate, with an acidic to neutral reaction. For indoor cultivation, RHS recommends a peat-free multipurpose growing 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 feeding from early summer through summer.

Propagation

Propagation can be by division, by separating rooted stolons or plantlets on stolons, or, at species level, by spore; vegetative propagation better maintains the characteristics of named cultivars. A single source reports that spores occur on the undersides of the fronds as regularly arranged dark brown to black dots.

Common problems

Possible pests include scale insects, spider mites, and Florida fern caterpillar. Dry growing medium and insufficient air humidity impair growth, while excessive winter watering can cause root rot and prolonged wetness of the fronds can cause rot. It is generally reported to prefer warmth; frost may make the above-ground fronds appear completely dead, although they may regrow in spring in suitable hardiness zones, and strong direct sunlight should also be avoided.

Identification

The fronds are pinnately compound and narrowly lanceolate, with auriculate, asymmetric pinna bases and round sori positioned on the veins. It resembles Nephrolepis cordifolia, but sources indicate that the stolons of Nephrolepis exaltata do not form 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