In warm climates, such as USDA Zones 9 through 11, Boston fern can grow up to 7 feet tall outdoors. Most Boston fern, however, are grown indoors. To propogate a Boston fern (Nephrolepis exaltata 'Bostoniensis), divide the roots.
Most home gardeners do not propagate ferns through spores or seeds because it is a very challenging process. Instead, gardeners divide the healthy plants that they already have. The process of division includes cutting the fern's root ball and replanting the divided parts into new pots. Using clean tools, containers and fresh potting soil will keep your equipment sterile and your plants disease-free.
Prep Tools and Work Environment
Spread clean plastic sheeting over the work area. Spray or mist your cutting tool with rubbing alcohol and allow the tool to air dry before cutting into the plant.
Remove the plant from the pot
Turn the plant over in one hand. Tap the side and bottom of the container to loosen the soil. You can also run a clean knife along the inner edge of the container to loosen the root ball from the original container. Work the plant from the container with your hands, always taking care to handle the plant at its base and not pull at extended fronds.
Divide the root ball
Cut the root ball into quarters. Spread the roots out a bit prior to cutting. Make certain that each quarter section has a healthy and even number of leaves.
Pot the divided plants
Mist the roots of each plant with water before potting in clean, loose, porous potting soil. The soil should be evenly moist, or crumbly to the touch.
Check the soil daily to ensure it remains evenly moist. Mist the plant regularly for the first few weeks.
Healthy ferns need room to grow. It is recommended that you divide your fern "every few years in spring."