Ferns are among the most ancient of plants and reproduce through spores rather than seeds. Plant growth varies from very fast to moderately slow, depending on the variety and growing conditions. Houseplants grow more slowly than those growing as landscape plants or those found in natural settings.
Houseplants vary in their growth, but a Boston fern placed on a partially shaded porch can grow 6 to 18 inches in one summer. During the winter months, ferns grown as houseplants grow more slowly and may drop their leaves. Reduce watering somewhat and keep them in a cool room to help them adjust to indoor conditions.
Ferns grow outdoors year-round in warm, humid climates, spreading quickly and growing 2 to 3 feet in one season. They may require division after two to three years to keep the plant growing vigorously. Boston ferns are native to the Southern U.S., but some non-native exotic ferns, such as the sword fern, have escaped cultivation to become invasive plants. These ferns grow quickly, outcompeting native vegetation. Do not plant these species outdoors and use Boston ferns with care near natural settings.
Growing conditions influence how fast a fern grows. Houseplants grow most vigorously near an eastern or northern window with bright, but indirect light. Watering practices vary, depending on the variety. Allow the soil to dry out between waterings to keep Boston ferns healthy, but water maidenhair ferns and button head ferns so the soil stays evenly moist. Ferns grown indoors appreciate temperatures below 72 degrees Fahrenheit, with a relative humidity level between 40 and 50 percent. Run a humidifier to increase humidity if necessary. Outdoor ferns grow best in partial to full shade, in rich, moist soil. They are winter hardy in frost-free climates only.
The fastest way to grow new ferns is by dividing a large plant. Dig up a plant in early spring or remove a large plant from its pot. Carefully separate the tubers or roots with a sharp knife. Replant the pieces in moist, well-drained soil or in two pots. Ferns also grow from spores, although the process takes at least one year to produce small plants. Shake spores from the undersides of the fern leaves into a tray. Spread the spores on ground sphagnum moss placed in a pot. Mist the moss to keep it evenly moist and cover the container with plastic wrap. Place it in a location with bright, indirect light and mist it frequently. Transplant the fern into potting soil six months after it germinates.