Tree ferns look more like palm trees than ferns, with large fronds splaying out from the tips of hairy trunks. Although they can reach 50 feet in their native habitats, they probably won't grow taller than 20 feet elsewhere. They thrive outdoors only in U.S. Department of Agriculture plant hardiness zones 8 to 11 for Tasmanian tree ferns (Dicksonia spp.) and USDA zones 9 to 11 for Australian (Cyathea spp.) types. Dicksonia species are frequently sold as unrooted trunk cuttings.
Select a location for your tree fern in the shade of taller trees, but where some sunlight will still reach the fern in the early morning or late afternoon. Find a site with loose, humus-rich soil, near a body of fresh water, if possible. This helps raise humidity levels around the plant. Make sure the fern will also be protected from strong winds.
Plant a rooted tree fern in late spring or early summer at the same height it grew in its container and 5 feet from the next fern or other plants. Pile composted manure a couple inches deep around the plant as a mulch, but don't allow it to make contact with the trunk.
Plant a tree fern trunk cutting by digging a hole to a depth about one-third the height of the cutting. Place the lower third of the cutting in the hole, and pack soil tightly around it. Push a sturdy garden stake into the ground behind the cutting, and attach it securely to the stake with garden twine.
Water the tree fern or cutting immediately, adding 2 tablespoons of liquid kelp to each gallon of water. Pour the solution over the crown or tip of the fern or cutting. Use about a gallon -- or however much it takes to soak the sides of the trunk and wet the soil around its base as well.
Continue to water the tree fern or cutting daily from its top until it begins producing new growth. Afterward, make sure it gets at least an inch of water per week, and feed it once a week with the kelp solution until mid-summer. Mist the fern frequently also, especially when the air is dry.