A graceful Boston fern is a welcome sight on a shady porch when the weather is pleasant, but will it last in cold weather? The Boston fern is a perennial plant hardy in USDA plant Hardiness Zones 9 to 11. In cooler zones, the location of the plant has a lot to do with its cold-weather survival until it is time to ultimately bring it inside for the winter.
A Boston fern on the southwest side of the house, where it is sheltered from cold northwesterly winds, has a good chance of survival when the mercury drops to 22 to 24 degrees.
On the northwest side of a house, a Boston fern may survive temperatures from -3.33 degrees C to -2.22 degrees C. Remember that while an outdoor thermometer may indicate this temperature range, wind chill still may make your fern too cold to survive.
If and when you do need to move your Boston fern indoors because of frigid temperatures, keep its atmosphere humid. Without enough humidity, it can lose its leaves during a season indoors. Use a humidifier, or place the pot in a saucer filled with pebbles and a bit of water. Mist the fern's fronds several times a day to combat the drying heat in a winter home.