Boston Fern (Nephrolepis): Cultivation, Care

Botany

The Nephrolepis, better known as the Boston fern, belongs to the Nephrolepidaceae family or, according to some classifications, to the Dryopteridaceae family. Its scientific name comes from the Greek nephros, meaning “kidney”, and lepis, meaning “scale”, referring to the characteristic shape of its sori, the structures containing spores located on the underside of the fronds.

In its natural habitat, Nephrolepis grows in tropical and subtropical climates, often in humid undergrowth or as an epiphyte on other plants. It is found in Central and South America, Southeast Asia and Australia, where it thrives in a warm and humid atmosphere. Generally not hardy, it is grown indoors here, in a conservatory for example, where its pretty foliage persists in winter. The genus includes about thirty species. Among the most commonly cultivated species are:

• Nephrolepis exaltata, the most widespread, whose famous ‘Boston’ variety is prized for its gracefully arched fronds.
• Nephrolepis cordifolia, distinguished by its hardiness down to -8°C and a more compact habit.
• Nephrolepis obliterata, sometimes called the Kimberley fern, with stiffer fronds.

Nephrolepis obliterata Kimberley

Nephrolepis exaltata boasts numerous cultivars with varied silhouettes, each with its own particular charm:

• ‘Bostoniensis’: seduces with its long bright green fronds and generously trailing habit.
• ‘Green Lady’: renowned for its thicker, slightly undulate fronds, it offers a lush and dense appearance.
• ‘Duffii’: displays compact fronds with round, shiny leaves, ideal for those seeking an original touch.
• ‘Fluffy Ruffles’: known for its highly divided and curly fronds, bringing a unique and airy texture.
• ‘Teddy Junior’: a dwarf version with short, dense fronds, perfect for small spaces or terrariums.
• ‘Whitmanii’: features wider, more robust fronds, with vigorous growth and a beautiful green colour.

Nephrolepis exaltata

Nephrolepis is a perennial fern that forms a dense, elegant clump with an upright habit, reaching about 50 cm in height. It spreads indefinitely thanks to a running rhizomatous system. In pots, its expansion will be contained.

The foliage stands out for its fineness and elegance, composed of soft, elongated fronds, finely divided, giving the plant a light and airy habit. These fronds, measuring up to 50 cm long in a mature plant, are typically arched and emerge from a thin yet sturdy central rachis. The pinnae, or leaflets, that make up each frond, are inserted in an alternate or opposite manner depending on the species. They are narrow, lanceolate, and often slightly asymmetrical at their base. Their edges can be entire, finely crenate or delicately undulate, enhancing the delicate appearance of the foliage. Each pinna is traversed by a prominent midrib, which structures the leaf and contributes to its flexibility. In Nephrolepis exaltata, the emblematic species of the genus, the fronds are particularly long and supple, adopting a naturally trailing habit.

The colour of the foliage varies according to growing conditions, ranging from bright green, tender to deep green, sometimes tinged with slightly glaucous hues. The surface of the fronds is smooth and sometimes subtly glossy.

Like all ferns, Nephrolepis produces neither flowers nor fruits and reproduces by spore dispersal. These spores form under the fronds, grouped within structures called sori. In Nephrolepis, these sori are covered by membranous indusia, small protective scale-like structures that regulate spore release at ripeness.

Nephrolepis exaltata (© Forest and Kim Starr)

Appreciated for its dense and airy foliage, this fern is also valued indoors for its ability to humidify the air and absorb certain toxins present in the atmosphere, such as formaldehyde and xylene. It is therefore ideal for improving air quality in homes and apartments.

Main species and varieties

Nephrolepis cordifolia Artic Jungle - Boston Fern

The hardiest among this genus of ferns, it also adapts well to indoor conditions or in a conservatory.

• Height at maturity 50 cm

See the product sheet

Growing Nephrolepis Indoors

Where to place a Boston fern indoors?

Nephrolepis enjoys bright, but indirect light. It should be placed in partial shade, ideally near an east or north-facing window. Too much direct light may scorch its foliage, while insufficient light will make it less dense and vigorous. It prefers an ambient temperature between 18 and 24°C and cannot tolerate temperatures below 12°C. Humidity should be high, as dry air can cause the fronds to turn brown. To maintain good humidity levels, it is advisable to mist its foliage regularly or place the pot on a tray of damp clay pebbles.

When to pot a Boston fern?

The Boston fern can be potted all year round indoors, but spring is the ideal time to allow it to adapt well to its new environment.

How to pot it?

The choice of pot is important: it must have drainage holes at the bottom to ensure good drainage. An unglazed terracotta pot is recommended, as it allows better evaporation of excess moisture. Its size should be slightly larger than the root ball, without being too big to prevent water from stagnating in an overly voluminous substrate.

Which substrate to choose?

Nephrolepis needs a substrate that is light, well-draining and rich in organic matter. A good mix can be made with equal parts of:

• Potting compost
• Turf or sphagnum moss, to retain moisture without suffocating the roots
• Perlite or sand, to improve drainage

Steps for potting

1. Choose a pot with drainage holes to allow water to escape.
2. Place a drainage layer (2-3 cm of clay pebbles or gravel) at the bottom of the pot.
3. Partially fill the pot with the prepared substrate.
4. Position the root ball in the centre of the pot without burying the base of the fronds.
5. Add substrate around the roots, lightly firming it down.
6. Water moderately, to moisten the substrate without waterlogging it.
7. Place the plant in its final position, avoiding draughts and direct heat sources like radiators.

Nephrolepis cordifolia

Planting in a terrarium

The Boston fern is not ideal for a closed terrarium, but it can thrive very well in an open terrarium. This plant loves humidity, but it also needs good air circulation to prevent excess moisture that could encourage mould growth or yellowing of its fronds.

In an open terrarium, it creates a stunning mini-jungle effect with its trailing foliage. Simply ensure it has a well-draining substrate, made of light potting compost mixed with perlite or coconut fibre, to prevent the roots from staying too wet. A thin layer of gravel or clay pebbles at the bottom of the container is recommended.

Cultivation and Care of Boston Fern Indoors

The Nephrolepis, or Boston fern, is a robust plant, but it requires minimal attention to maintain dense and vibrant foliage. Its care mainly relies on appropriate watering, regular fertilisation, sufficient ambient humidity and periodic repotting.

Watering: how and how often?

The Nephrolepis prefers a slightly moist substrate, but never waterlogged. Watering should be regular and moderate to avoid root rot.

• During the growth period (spring-summer): water 2 to 3 times a week, allowing the surface of the substrate to dry slightly between waterings.
• In autumn and winter: reduce watering to once a week, or even less if the room is cool, while maintaining good ambient humidity.

The water used should be non-calcareous (preferably filtered, demineralised or rainwater) and at room temperature to avoid thermal shock to the roots.

Misting

The Boston fern needs a humid environment: mist daily, especially in winter.

Fertilisation: when and how to feed the Nephrolepis?

A nitrogen-rich liquid fertiliser is essential to maintain dense, lush green foliage.

• In spring and summer, add a liquid fertiliser for green plants every two weeks, diluted by half to avoid nutrient overload.
• In autumn and winter, space out applications to once a month, or even suspend fertilisation if growth slows.

Pruning: should fronds be cut?

The Nephrolepis does not require strict pruning, but it is advisable to regularly remove dry or yellowed fronds to stimulate the growth of new shoots and maintain a beautiful shape. A clean cut at the base with disinfected scissors is sufficient.

Repotting: when and how to do it?

Repotting is necessary every 1 to 2 years, in spring, when the roots fill the pot or the fern appears cramped. Repotting can also be an opportunity to divide the clump and propagate the plant. A slightly larger pot than the previous one will ensure continuous growth without excess moisture.

• Choose a slightly larger pot, with drainage holes.
• Use a light, well-draining substrate, composed of potting soil for green plants, turf and perlite.
• Divide the plant if it is too large, carefully separating the rootstocks to obtain several new young plants.
• Water lightly after repotting and maintain good ambient humidity to facilitate adaptation.

Pests and Diseases of Nephrolepis

The Nephrolepis is a relatively hardy plant, but unsuitable growing conditions can encourage the appearance of parasitic organisms and diseases. Excess moisture, overly dry air or poor ventilation can weaken the plant and make it more vulnerable.

Common Parasitic Organisms

•  Mealybugs: these small white, cottony insects attach themselves to stems and the underside of fronds, causing the plant to weaken. You can remove them with a cotton pad soaked in 70° alcohol or by spraying a mixture of water and black soap.
• Aphids : they sometimes attack young shoots, distorting and weakening them. A soapy water spray or an infusion of black soap and garlic can help get rid of them.
• Thrips: these small black or translucent insects pierce the fronds, causing discoloured spots to appear. A treatment based on black soap or neem oil can be effective.
• Spider mites:  they mainly appear when the air is too dry, causing fronds to yellow and small webs to form under the leaves. Increasing ambient humidity by misting the plant regularly limits their spread.

Common Diseases

• Root rot: this occurs due to overwatering or poor drainage. The roots turn black, the fronds yellow and droop. You should then repot the plant in a more free-draining substrate and space out watering.
• Fungal spots: excess moisture or poor ventilation can encourage the appearance of brown or black spots on the fronds. A spray of horsetail decoction or diluted baking soda can limit their spread.
• Yellowing or drying foliage: this is not a disease, but often a sign of stress due to lack of humidity, insufficient watering or cold draughts. The Boston fern is very sensitive to dry air. Checking growing conditions and adjusting care usually helps the plant recover.

Prevention and Good Practices

• Avoid overwatering and ensure the pot has good drainage.
• Regularly inspect the foliage to detect early signs of parasitic infestation.
• Occasionally wipe the fronds with a damp cloth to remove dust and limit pest proliferation.

Propagation of Nephrolepis

Separating stolons is the simplest and most effective method to propagate Nephrolepis, unlike sowing spores, which requires specific conditions and a lot of patience.

1. Propagation by stolons

The Nephrolepis produces stolons, long creeping stems that give rise to new young plants. This method is ideal for propagating the plant without disturbing the main root ball. It allows you to obtain already developed young plants, ready to be grown in pots.

Steps:

1. Identify a stolon with a small rosette of leaves at its tip.
2. Using clean secateurs, cut the stolon, leaving a small margin on either side of the seedling.
3. Immediately transplant into a pot filled with a light, well-draining substrate. Place the roots on the surface and cover lightly without compacting too much.
4. Water lightly to moisten the substrate, without soaking.
5. Place the pot in a bright spot, but out of direct sunlight, with a humid atmosphere.
6. Keep the soil slightly moist and mist the fronds if the air is dry. After a few weeks (around 3 to 4 weeks), the new plant will start producing new fronds, a sign of successful establishment.

2. Propagation by fern spores

Sowing fern spores remains a longer and more unpredictable process. Alexandra details the technique for successfully sowing spores.

How to showcase it in your interior?

To perfect this display, the choice of container plays a key role. A wicker basket or terracotta planter highlights its natural and authentic side, while a ceramic pot with clean lines gives it a more contemporary look. Its delicate foliage pairs particularly well with natural materials like rattan or macramé.

Placed near a soft light source, without direct sunlight, it maintains its radiance and unfurls its fronds elegantly. Ambient humidity is its ally, making it an ideal candidate for rooms where you want to create a cool and soothing atmosphere. In a bright bathroom, it finds the perfect setting where humidity enhances its shine and intensifies this lush jungle atmosphere.

Next to more rigid foliage like a snake plant (Sansevieria), the contrast is superb!