Fern houseplants require constant warmth and a humid environment in order to thrive indoors. Ferns originate in tropical and sub-tropical areas and require a steady temperature of 60 to 70 degrees Fahrenheit during the day and 50 to 60 degrees Fahrenheit at night.
Place the plants in an area that receives two to four hours of sunlight each day, such as a north-facing window. To increase the humidity around the plants, fill a shallow tray with pebbles, and add water to almost cover the pebbles. Place the plants on top, and refill the water as needed.
Water the ferns each week, allowing the soil to dry out slightly between applications. Reduce the amount of water the plants receive in the winter months when their growth slows. Feed ferns a liquid houseplant fertilizer once a month during the growing season in the months of April through September. Don't feed the plants in the winter, when their growth decreases.