Boston fern (Nephrolepis exaltata), commonly known as sword fern, is a versatile and attractive houseplant known for its arching fronds and air-purifying qualities. A favorite among indoor gardeners, this plant thrives with minimal care, preferring indirect light and high humidity. Boston ferns can thrive outdoors in warm, shaded gardens, making them ideal for regions with humid climates like Southern California or Florida.
Here’s everything you need to know to keep your Boston fern healthy and flourishing.
Overview of Boston Fern
Boston Fern is a classic, low-maintenance plant that brings a touch of tropical beauty into any space. With its lush, arching fronds and impressive air-purifying abilities, this sword fern is a favorite for indoor and outdoor settings alike. Known for its durability, Boston fern flourishes in humid environments and adds vibrant greenery to partially shaded areas in gardens or homes. Below is an overview of its basic characteristics to help you better understand its needs and unique appeal.
- Common Names: Boston fern, sword fern, ladder fern, boss fern
- Botanical Name: Nephrolepis exaltata
- Family: Lomariopsidaceae
- Type: Perennial, Herbaceous
- Mature Size: 2-3 ft. tall and wide
- Sun Exposure: Partial, indirect light
- Soil: Moist, well-drained, slightly acidic
- USDA Hardiness Zone: 9-11
Boston Fern Care Essentials
Light Requirements
Boston fern thrives best in bright, indirect light. While it can tolerate some morning sunlight, exposure to intense, direct sun, especially in the afternoon, can scorch its delicate fronds. Too little light, however, will result in sparse growth and dull-looking fronds. For indoor settings, a north-facing window is ideal, providing consistent filtered light without direct sun exposure. Outdoors, Boston ferns do well on shaded porches or patios, where they receive dappled sunlight in the morning and shade in the afternoon. Using sheer curtains or placing them in areas with indirect sun ensures they get the ideal light conditions.
Soil
Boston ferns thrive in rich, loamy soil that offers excellent drainage. Good soil structure is essential because these ferns need moisture but are sensitive to waterlogged conditions. Adding compost and peat moss enriches the soil, helping retain moisture and aerate the roots for healthy growth. For potted Boston ferns, a peat-based potting mix with added perlite or sand improves drainage, preventing water from pooling at the roots. This soil combination allows the fern to absorb adequate nutrients while avoiding root rot, which can occur in poorly draining soil.
Watering
Proper watering is crucial for the health of a Boston fern. During its active growing season (spring and summer), keep the soil consistently lightly moist. The soil should feel damp to the touch but never soggy. In hot or dry conditions, the fronds may wilt or develop brown tips if the soil dries out too much. To check moisture levels, insert a finger about an inch deep into the soil—water if it feels dry at that depth. In the fall and winter, reduce watering as the fern enters a dormant phase. Overwatering during this period can lead to root rot, so allow the top inch of soil to dry out slightly before watering again.
Temperature and Humidity
Boston ferns prefer temperatures between 65°F and 75°F. They are highly sensitive to temperature fluctuations, particularly cold drafts or exposure to high heat. Temperatures above 95°F or below 35°F can stress the plant. Humidity is also vital; Boston ferns thrive in high humidity levels, ideally above 80%. In drier indoor environments, consider misting the plant regularly, setting it on a humidity tray filled with pebbles and water, or using a humidifier nearby. This is especially important if your home has dry air from heating or air conditioning systems, which can cause the fronds’ tips to turn brown due to lack of moisture.
Fertilizing
Fertilizing Boston ferns ensures they receive adequate nutrients for robust growth, particularly during the active growing season. Outdoor ferns benefit from a thin layer of compost and mulch in early spring, which enriches the soil naturally as it breaks down. Indoor ferns, however, may need a 20-10-20 liquid fertilizer diluted to half strength, applied once a month from spring through summer. Avoid fertilizing in the fall and winter, as the plant’s growth slows, and excess nutrients during dormancy can cause more harm than good, potentially leading to burnt roots or nutrient buildup.
Types of Boston Fern
Various Boston fern varieties offer different aesthetic qualities, making it easy to find one that suits your space:
- Nephrolepis cordifolia ‘Duffii’: A dwarf Boston fern with a lemony scent, perfect for small indoor spaces.
- Nephrolepis exaltata ‘Compacta’: This hardy, compact type withstands mild dryness and heat, making it versatile.
- Nephrolepis exaltata ‘Florida Ruffle’: Known for its ruffled fronds, this variety thrives in very humid environments.
- Nephrolepis exaltata ‘Golden Boston’: A golden-leafed fern that’s great for outdoor pots; it can be overwintered indoors.
- Nephrolepis exaltata ‘Rita’s Gold’: Chartreuse fronds give this fern a glowing look, especially in shaded garden containers.
Pruning Boston Fern
Pruning is essential for maintaining the lush appearance of your Boston fern and helps prevent a leggy, sparse look. Regular pruning encourages the plant to grow more densely, giving it a full, vibrant appearance. Start by removing any dead, yellowing, or damaged fronds at the base of the plant, which not only keeps it looking tidy but also allows it to redirect energy to healthier growth. Use sharp, clean shears to make precise cuts close to the soil surface, avoiding damage to the surrounding healthy fronds.
For an even fuller, bushier appearance, focus on trimming the edges of the fern. Avoid pruning the top or central part of the plant, as this can disrupt its natural shape and lead to uneven growth. Instead, carefully clip around the outer edges to your desired shape, which encourages lateral growth and enhances the fern’s characteristic arching form.
The ideal time to prune is during repotting, as it stimulates new growth and gives you a chance to inspect the root system for any signs of root rot or overcrowding. After pruning, place the fern in a humid, well-lit environment to support recovery and encourage vigorous new growth. Regular pruning, about once every few months, will help your Boston fern maintain its attractive, lush appearance throughout the year.
Potting and Repotting
Boston ferns thrive in containers that retain moisture well, helping them stay hydrated without becoming waterlogged. Plastic or glazed ceramic pots are excellent choices, as they hold moisture longer than unglazed terracotta pots. Additionally, ensure the pot has ample drainage holes to prevent water from accumulating at the bottom, which can lead to root rot.
Repotting is generally needed every 1-2 years, or when you notice roots beginning to crowd the pot and poke through the drainage holes. The best time to repot is in the spring, as this is the start of the growing season, allowing the fern to quickly adjust and establish itself in the new container.
When choosing a new pot, select one that is only 2 inches larger in diameter than the previous pot. An oversized pot can hold too much soil, leading to poor drainage and potentially soggy conditions. Fill the new pot with fresh peat-based potting mix blended with perlite for aeration, or use a high-quality potting soil designed for ferns.
To repot, gently remove the fern from its current pot, taking care to loosen any tightly wound roots. Place it in the new pot and fill around the root ball with the fresh mix, ensuring the fern is planted at the same depth as before. After repotting, water the fern thoroughly to settle the soil and help eliminate any air pockets around the roots.
Place the newly repotted fern in a location with bright, indirect light to reduce the risk of transplant shock. Avoid direct sunlight, which can stress the plant during this adjustment period. Maintain regular humidity levels by misting or placing the pot on a humidity tray, especially if the fern was recently disturbed. Proper repotting gives Boston ferns the space they need to grow and flourish, resulting in healthier, more vigorous fronds.
Propagation
Propagating Boston ferns is most effectively done through division, a straightforward method that rejuvenates older plants while creating new ferns for your garden or home. Division is especially useful when the plant has outgrown its current pot or space in the garden. Early spring is the ideal time to propagate, as the plant is beginning its active growing season, which helps the divisions establish themselves quickly.
To propagate by division, begin by carefully removing the Boston fern from its container or, for garden-grown plants, gently digging around the base to free the roots. Use a sharp, sterilized garden trowel or knife to separate a healthy clump with a good number of fronds and a well-established root system. Look for divisions with visible new growth, as these are likely to root more successfully.
Steps for Propagating Indoor Boston Ferns
- Prepare a new pot with fresh, moist potting soil. A peat-based mix with added perlite is ideal, providing both moisture retention and good drainage.
- Place the divided clump into the new pot, setting it at the same depth it was growing previously to avoid stress.
- Backfill around the roots with potting soil, gently pressing down to secure the plant and remove any air pockets.
- Water thoroughly until excess water drains out from the bottom, ensuring the soil is evenly moist.
Steps for Propagating Outdoor Boston Ferns
- Select a shaded garden area with rich, loamy soil that drains well. Prepare the spot by loosening the soil and mixing in compost to improve nutrients and moisture retention.
- Dig a hole large enough to accommodate the division and set it in at the same level as the original plant.
- Backfill with soil, firming it gently around the roots to prevent the division from shifting.
- Water the new division well, making sure the soil remains moist, especially in the initial weeks.
Aftercare for New Fern Divisions
Place indoor divisions in indirect, bright light and mist regularly to maintain humidity, which helps the fern recover from the transplanting process. Outdoor divisions should be kept in a shaded spot, where the soil stays evenly moist.
After a few weeks, check for new growth as an indication that the fern has successfully established itself. This easy method of propagation allows you to enjoy multiple Boston ferns while keeping the parent plant healthy and well-maintained.
Growing from Spores
Growing Boston ferns from spores can be a fascinating process, though it requires patience and careful attention. Like other ferns, Boston ferns don’t produce seeds; instead, they reproduce via tiny spores found on the underside of mature fronds. Growing them this way allows you to propagate the plant from scratch, though it may take several months to see a fully developed fern.
Step-by-Step Guide to Growing Boston Ferns from Spores
- Collect the Spores:
- Choose a healthy, mature Boston fern with fronds that have brown spore cases (sori) on their undersides. These sori contain the spores needed for propagation.
- To collect, place a sheet of paper or a tray beneath the frond and gently shake it. The spores will fall as a fine dust onto the paper. If they don’t release immediately, let the frond dry in a cool, dark place for a day or two, then shake it again.
- Prepare the Planting Medium:
- Use a shallow pot or seed tray filled with a mixture of moist compost and peat moss. This mixture provides the organic matter and moisture retention needed for the spores to germinate.
- Level the surface of the soil to create a smooth, even bed for sowing the spores. Lightly moisten the soil using a spray bottle to avoid disturbing the spores when you sprinkle them on top.
- Sow the Spores:
- Evenly distribute the spores across the surface of the prepared soil, keeping them close to the surface, as they need light and humidity to germinate.
- Avoid covering them with soil, as they will germinate better when exposed to light. Lightly mist the soil to settle the spores and create a humid environment.
- Create a Humid Environment:
- Cover the pot or tray with plastic wrap or a clear plastic lid to maintain high humidity levels. If using plastic wrap, poke a few small holes to allow for slight airflow, which helps prevent mold growth.
- Place the tray in bright, indirect light; avoid direct sunlight, as it can overheat the spores.
- Mist Regularly and Monitor Growth:
- Mist the soil daily to keep it consistently moist but not soggy. Within a week or two, you may see a fine green carpet-like layer forming on the soil’s surface—this is the prothallia, the first stage of fern growth.
- The prothallia will develop into tiny heart-shaped structures that contain both sperm and eggs. Keep the soil and air moist to encourage fertilization, which happens naturally when water is present.
- Wait for Sporophyte Growth:
- Once fertilization occurs, the tiny prothallia will begin to develop into young ferns, known as sporophytes. This stage can take several weeks to a few months, depending on conditions.
- Continue misting and maintaining a warm, humid environment until you see tiny fern fronds emerging.
- Transplant the Young Ferns:
- Once the young ferns have grown a few inches tall and developed several fronds, they can be carefully transplanted into individual pots or into your garden.
- Use a peat-based potting mix for indoor plants or enriched garden soil with compost for outdoor planting. Handle the delicate young plants with care during transplanting to avoid damaging their roots.
Growing Boston ferns from spores requires dedication but is rewarding, allowing you to grow lush, new ferns entirely from scratch. With proper care, the tiny plants will gradually develop into mature Boston ferns, adding beauty and greenery to your home or garden.
Overwintering Boston Fern
To prepare a Boston fern for winter, trim back fronds to about 4 inches and place it in a cool, dry area, watering just once a month. Outdoor ferns can be cut back in fall, mulched, and watered occasionally through the winter to keep the soil from drying out.
Common Pests and Diseases in Boston Ferns
Boston ferns, though generally resilient, can occasionally fall prey to pests and diseases, especially when grown outdoors. Common pests such as whiteflies, mealybugs, snails, slugs, and caterpillars may target Boston ferns, causing visible damage to the delicate fronds and stems.
Managing Outdoor Pests
- Whiteflies and mealybugs: These tiny insects feed on plant sap, leaving behind a sticky residue that can attract mold. They weaken the plant by reducing its nutrients, causing yellowing leaves and stunted growth.
- Solution: Rinse the fronds with a steady stream of water, dislodging these pests. Repeat as needed, focusing on the undersides of the fronds where pests tend to gather. For heavier infestations, apply an organic insecticidal soap or neem oil spray, taking care to avoid spraying in direct sunlight to prevent leaf burn.
- Caterpillars, snails, and slugs: These pests chew through the fronds, creating holes and ragged edges, and leave slimy trails on the foliage.
- Solution: Inspect the plant regularly and handpick visible pests. For snails and slugs, setting out beer traps or placing crushed eggshells around the base can deter them naturally.
Common Indoor Pests
Indoor Boston ferns are usually safe from larger pests, but they can be affected by fungal infections, especially in humid or poorly ventilated environments. The most common issue is blight, a fungal infection that appears as brown web-like mycelium on the fronds.
- Solution: Improve air circulation by spacing plants apart and avoiding excessive misting. Repot the fern in fresh, sterile soil and clean its container to remove any fungal residue. If the infection persists, consider using a mild fungicide as a last resort.
Common Problems and Troubleshooting in Boston Fern Care
Proper care can prevent many common issues in Boston ferns, but here’s how to address a few of the most frequent problems.
- Yellowing Fronds:
- Cause: Often a result of overwatering, yellowing fronds are usually due to root rot or poor drainage. Overly wet soil prevents oxygen from reaching the roots, weakening the plant.
- Solution: Check the pot’s drainage holes and repot if necessary, using fresh, well-draining potting mix. Only water when the top inch of soil feels dry, allowing excess water to fully drain.
- Brown Leaf Tips:
- Cause: This is usually due to low humidity levels, as Boston ferns require consistently high humidity (around 80%) to thrive.
- Solution: To boost humidity, place the pot on a pebble tray filled with water, ensuring the pot sits above the water level rather than in it. Regular misting also helps, especially in dry indoor environments, or consider using a humidifier in rooms with especially low humidity.
- Drooping or Wilting Fronds:
- Cause: Drooping fronds may indicate underwatering or a lack of humidity. In some cases, it could also signal temperature stress.
- Solution: Check the soil moisture; if dry, water the plant thoroughly. Keep the fern in a location where temperatures are stable and avoid placing it near heating vents, air conditioners, or drafty areas.
- Slow Growth or Sparse Fronds:
- Cause: This may be due to insufficient light or nutrient deficiency.
- Solution: Move the fern to a spot with bright, indirect light and feed it with a diluted liquid fertilizer during the growing season (spring and summer). Avoid placing it in direct sunlight, as this can burn the fronds.
With careful attention to humidity, proper watering, and pest management, your Boston fern can stay healthy and vibrant year-round. Regular inspections will help catch any issues early, allowing for quick solutions and a flourishing fern.
Conclusion
Boston ferns are among the most rewarding plants for both beginners and seasoned gardeners. With a little attention to light, water, and humidity, these ferns will reward you with lush, green fronds year-round, purifying your indoor air and beautifying your home or garden space. By following these care tips, you’ll enjoy the elegance and vitality of a Boston fern for years to come!
