The Boston fern (Nephrolepis exaltata) is a tropical perennial prized for its lush, arching, green fronds. Since it is only hardy in USDA Zones 9 through 11, it cannot withstand the frost or freezing temperatures of cooler climates. Fortunately, the Boston fern transitions well to an indoor setting, allowing you to keep the plant alive until the following spring. With proper preparation, the fern can survive the winter indoors, providing a touch of green until it returns outside.
Preparing the Fern for Indoor Transition
The transition indoors should happen well before the first hard frost, ideally when nighttime temperatures consistently dip below 50°F (10°C). Bringing the plant inside too late risks frost damage, which can harm the fronds or kill the plant. Before moving the fern inside, a thorough cleaning and inspection is necessary to prevent introducing outdoor pests into your home.
Start by hosing down the entire plant vigorously, focusing on the undersides of the fronds and the soil surface. This helps dislodge common pests like spider mites, scale, and mealybugs. After rinsing, carefully inspect the foliage for lingering insects or fine webbing. This is also the time to prune the fern, removing any dead, yellowed, or overly long fronds to tidy the plant and eliminate potential pest hiding spots.
Essential Indoor Environment Requirements
Once inside, the Boston fern requires a specific microclimate that mimics its native tropical habitat to successfully overwinter. The plant needs bright, indirect light. An ideal location is near a north or east-facing window, or offset from a south-facing window to prevent scorching. Direct, harsh sunlight can quickly burn the foliage, resulting in brown tips and edges.
The ideal temperature range for the fern is between 60°F and 75°F, and temperatures should not drop below 55°F. The greatest challenge indoors is the low humidity of heated homes, which often falls below the 50% minimum the plant prefers. To counteract this, use a humidifier, group the fern with other plants to create a localized humid environment, or set the pot on a pebble tray filled with water.
Winter Care and Maintenance
During the cooler months, the Boston fern’s growth naturally slows down, requiring an adjustment to its routine care. This reduced growth means the plant needs less water than during the active summer season. Let the top inch of soil dry slightly before watering again, as overwatering is a common winter mistake that leads to root rot.
Fertilization should be ceased entirely from late fall through winter due to the plant’s semi-dormant state. The plant cannot efficiently absorb nutrients, and continued feeding can lead to a buildup of salts that damage the roots. Continuous monitoring for pests is necessary, especially for spider mites, which thrive in the warm, dry air of indoor heating and quickly cause stippling and yellowing of the fronds.