Calling an Australian tree fern (Sphaeropteris cooperi, also known as Cyathea cooperia) a houseplant is a bit like calling a leopard a housecat—in their native habitats, these plants grow to 40 feet or more, easily too large for most indoor growing situations, except for the largest of greenhouses. But they deserve inclusion because of their sheer beauty. These majestic ferns have curled fronds that emerge from the central leaf crown; individual fronds generally reach four or five feet or as much as 20 feet in outdoor plantings. A well-grown tree fern is a fast-growing plant, and will likely outgrow its space within a few years.
The trunk of the Australian tree fern starts out as a low, wide clump and spreads as much as six feet in a year before growing upward into a single slender trunk covered in glossy ginger-brown hairs. The fronds are broad, bright green with triangular lacy leaves and a foliage spread of 8 to 15 feet. Leaves don't change color in the fall, and there are no flowers or fruit.
This is one of the most commonly used tree ferns, but it is used mostly as a large potted ornamental in the U.S. Where it is grown outdoors, it is limited to public gardens and arboretums in tropical or semi-tropical zones. The plant has naturalized itself in Hawaii, where it is regarded as invasive due to its fast growth and prolific self-propagation.
This tropical plant is adaptable to a variety of climates but thrives best as a perennial in USDA plant hardiness zones 8 through 11, thriving between 65ºF and 80ºF. Australian tree ferns can tolerate a variety of soil conditions including acidic, sand, loam and clay, but prefer a moist soil rich in humus. Although these are shade-loving plants in general, they can also thrive in medium shade to full sun locations, whether exposed or sheltered. Australian ferns are not drought tolerant and need weekly watering, with high levels of moisture or humidity in dry weather. However, avoid watering the crown directly, as this can cause rot. These plants are tolerant of salty winds near coastlines, but not salty soil conditions. During growing season, feed with controlled-release fertilizer or biweekly with weak liquid fertilizer. Larger specimens are heavy feeders.
By spores. Propagation is typically left to growers.
Repot annually into larger pots with fresh, free-draining potting soil. When the plant reaches the maximum size allowed by the growing space, stop repotting to slow growth. Eventually, it will likely outgrow both the pot and the room.
The plant sold as an Australian tree fern is typically a Cyathea cooperi. There are, however, about 1,000 different kinds of tree ferns, all found in tropical or subtropical settings. The New Zealand or Tasmanian tree fern is closely related, but the species is actually Dicksonia antarctica. This plant tends to have a narrower crown than the Australian tree fern but has similar growth requirements.
Tree ferns thrive in mid-elevation tropical environments, where they can sometimes be found growing in great, prehistoric forests swathed in tepid mist. The key to growing a healthy tree fern is to provide ample humidity and consistency, avoiding extremes of heat, cold, and sunlight. Tree ferns don’t appreciate rapid changes in humidity or temperature, which will result in browning leaves. Beware of the tiny hairs on the trunks of Cyathea, as they can be irritating to the skin.