Boston fern (Nephrolepsis exaltata), also known as the feather palm or sword fern, grows as a dense, rapidly spreading ground cover where it survives outdoors in U.S. Department of Agriculture plant hardiness zones 8 through 11. You can also grow Boston fern as a houseplant to enjoy its graceful fronds. This vigorous fern quickly outgrows its planting containers, requiring division into multiple smaller sections or transplanting into larger containers. If you don't relieve the overcrowding, the plant will begin to suffer.
Water the Boston fern thoroughly a few hours before you transplant it. This makes the soil or medium around the root mass easier to work with and minimizes injury to the fern.
Mix together equal parts peat moss, sand and garden soil. Thoroughly blend and moisten the medium before using it with the fern. You can also use a specialty fern potting mix.
Place a few inches of the prepared growing medium in the bottom of one or more containers, depending on the number of divisions you plan to make. Make sure each container is clean and has drainage holes. If you are simply transplanting the fern into a larger container, choose a container no more than a few inches larger than the fern's current container.
Slide the fern out of its current container by turning the container on its side or upside down while cradling the soil surface with one hand.
Cut the root mass into halves or quarters, each with a proportionate amount of fronds. If you are simply transplanting the entire intact Boston fern into a larger container, you do not need to cut the root mass unless it is root-bound. If it is root-bound, with roots growing in a tight circle around the edge of the root mass, use a sharp knife to score the edges, making four vertical, 1-inch-deep cuts spaced evenly around the root mass and cutting an "X" into the bottom.
Set the Boston fern root mass in the center of the prepared container and add or remove medium under the roots to ensure it is planted at the same depth it was previously growing at. If you are planting just a section of the original root mass, fan the roots out slightly.
Water the transplanted fern in thoroughly and regularly, as needed, so the growing medium around the roots remains constantly moist but not soaking wet. Mist the fern periodically or otherwise maintain a high level of humidity around the plant. Once established, Boston ferns can tolerate occasional dry spells, but transplanted specimens require regular moisture.