The sword fern, commonly sold as the Boston fern (Nephrolepis exaltata), is a classic indoor houseplant known for its cascading, bright green fronds. Originating from warm, humid tropical and subtropical forests, this plant brings a lush, tropical feel to any space. While its dense foliage makes it a beautiful addition to the home, the sword fern requires specific environmental conditions to thrive indoors. Successful long-term cultivation depends primarily on understanding its needs for moisture and light.
Light and Temperature Requirements
Sword ferns prefer bright, indirect light, mimicking the dappled sunlight they receive under a dense forest canopy. An ideal placement is near an east-facing window, which provides gentle morning sun, or several feet away from a south or west-facing window. Avoid placing the plant in direct sun, especially harsh midday rays, as this will quickly scorch the delicate fronds, leading to brown tips.
These ferns thrive best in moderate, consistent temperatures, ideally ranging between 65°F and 75°F (18°C to 24°C). They are sensitive to sudden drops in temperature and cold air. Keep them away from exterior doors, drafty windows, and air conditioning or heating vents, as temperature fluctuations can stress the plant and inhibit healthy growth.
Watering and Humidity Management
The most significant challenge for indoor sword fern care is consistently meeting its high demand for moisture in both the soil and the air. The soil must be kept consistently moist but should never be allowed to become waterlogged or saturated, which leads to root rot. Water thoroughly when the top inch of the soil begins to feel dry to the touch.
During the active growing season in spring and summer, this often means watering more frequently, sometimes up to once a week, and reducing the frequency in the cooler, dormant winter months. When watering, ensure that the pot drains completely to prevent the roots from sitting in standing water, which starves them of oxygen.
Sword ferns require high ambient humidity, ideally above 50%, with some varieties thriving at 80% or higher. Low humidity is the primary cause of the common issue of brown, crispy frond tips. While misting can provide a temporary boost in moisture, it is often insufficient on its own and may even promote fungal growth on the leaves.
Methods to Increase Humidity
More effective methods to increase humidity include:
- Placing the fern on a shallow tray filled with pebbles and water, ensuring the pot sits above the water line.
- Grouping several houseplants together to create a localized microclimate with higher moisture levels.
- Using a small room humidifier, especially during the winter when indoor heating dries the air.
- Placing the fern in a naturally humid room, such as a well-lit bathroom.
Soil, Feeding, and Repotting
Sword ferns prefer a rich, well-draining potting mix that retains moisture without compacting easily. A good soil composition includes a peat-based mix combined with materials like perlite or vermiculite. These additions improve aeration and drainage while providing necessary organic matter and allowing for proper water flow.
These ferns are sensitive to salt buildup, which can burn their delicate roots. During the spring and summer growing season, feed the plant monthly or bi-monthly using a balanced liquid houseplant fertilizer diluted to half or even quarter strength. Stop all feeding during the fall and winter when the fern’s growth naturally slows down.
Repotting is typically necessary every two to three years or when the plant shows signs of being root-bound, such as circling roots or water running quickly through the soil. The best time to repot is during the spring, the start of the active growth period. Choose a new pot that is only one size larger than the current one and ensure it has adequate drainage holes.
Troubleshooting Common Problems
The appearance of brown, crispy tips on the fronds signals insufficient ambient humidity or inconsistent water. Increase humidity using a pebble tray or humidifier and check the watering schedule to ensure the soil is not drying out completely. Conversely, yellowing fronds are often a sign of overwatering, which causes the roots to suffocate and rot.
Should yellowing occur, check the soil saturation and allow the top inch to dry before watering again, ensuring the pot is draining properly. Pale or bleached fronds can indicate that the plant is receiving too much direct light, requiring a move to a more filtered location. Insufficient nutrients can also cause general yellowing, which may be corrected by applying a diluted fertilizer during the growing season.
Sword ferns are generally resistant to pests, but they can occasionally attract common houseplant pests like spider mites, scale insects, or mealybugs. Since spider mites thrive in dry conditions, increasing humidity often helps deter them. Regular inspection of the undersides of the fronds allows for early detection. Small infestations can be treated by wiping affected areas with a cotton swab dipped in rubbing alcohol or using an insecticidal soap.