Tree ferns
Tree ferns bring height, a tropical atmosphere and a cooling effect to the garden. Two familiar choices in Western Australia are Cyathea cooperi and Dicksonia antarctica.
Choose for the space you have
Both species grow in a range of soils and generally prefer acidic conditions, but their growth rates and preferred positions differ. Allow room for the mature crown and choose a position where moisture can be maintained.
For rapid growth: Cyathea cooperi
A fast-growing tree fern with spreading fronds. It needs generous overhead space and can soon outgrow a patio or shade-house roof. Established plants adapt to sun or semi-shade with adequate moisture and mulch.
For sheltered spaces: Dicksonia antarctica
The slower-growing Soft Tree Fern prefers shade or dappled light and protection from wind. It suits pots, tubs and sheltered garden positions, including patios and pergolas with enough space for its crown.
One important difference
Do not shorten C. cooperi by cutting its trunk. D. antarctica can regrow from a trunk cutting, but this is a rescue or relocation technique rather than routine pruning.
Cyathea cooperi
Straw Tree Fern • Scaly Tree Fern • Lacy Tree Fern • Coin Spotted Tree Fern
Origins and appearance
Native to Queensland and New South Wales, this species has also naturalised in south-western Western Australia. It is listed in Florabase under Sphaeropteris cooperi as alien to WA; its naturalised occurrence should not be confused with local native status.
Depending on conditions, it can reach about 10 m tall, with spreading fronds 1-4 m long. Its woody, fibrous trunk is usually around 15 cm across, and the lower trunk may be covered with root growth.
The distinctive coin pattern
This is a “self-cleaning” tree fern: dead fronds fall away, leaving oval scars at least the size of a 50-cent coin. The pattern varies with growing conditions. Plants in full sun often have thicker, more fibrous trunks with less obvious markings.
Allow for fast growth
New fronds develop almost continuously. Young plants need repotting as their fibrous root systems fill their containers. Avoid planting beneath low roofs: the crown can reach roof height within a few years.
Moving an established plant
If the fern becomes too tall for its surroundings, move it with its root ball intact. Do not saw through the trunk to reduce its height; this kills the plant. The original article suggests digging about 0.5-1 m around the base and retaining as much root ball as possible.
Remove most fronds when transplanting, taking care not to damage the unfurled croziers (new fronds). Replant with adequate mulch and moisture, particularly during warmer months.
Placement and propagation
Allow clearance from busy paths so people do not brush against the fronds. The original also advises keeping plants away from windows because they shed abundant spores. Propagation is by spores.
Dicksonia antarctica
Soft Tree Fern
A slower-growing choice
Native to Queensland, New South Wales, Victoria and Tasmania, this fern can eventually reach 15 m. Its roughly textured fronds are 2-4 m long, and the soft, fibrous trunk provides a support for epiphytic ferns and orchids.
Old fronds remain as a skirt around the trunk and can be removed with secateurs. Growth is slow, often with one flush of new fronds each year. It makes an effective single specimen or a group planting with trunks of different heights.
Position and establishment
Choose shade or dappled light with shelter from wind. This fern is often sold as a bare trunk, priced by its length. Select a specimen with intact unfurled croziers and protect them during planting. The original recommends planting the trunk approximately 30 cm deep.
Transplanting and trunk cuttings
D. antarctica can be transplanted, reducing the fronds when it is moved. Unlike C. cooperi, its upper trunk can form roots after being cut and replanted. Protect the crown and new fronds throughout.
The Australian National Botanic Gardens recommends trunk cutting only where a plant would otherwise be lost. The top can regrow, but the remaining base dies. Keep the replanted section cool and regularly watered while it establishes.
Propagation
Propagation is by spores or by plantlets that may develop around the trunk base.
Seasonal care for both species
Provide adequate water during warm growing months and mulch to help retain moisture. Apply organic or inorganic fertilisers during spring and early summer. The original recommends sheep or cow manure among the feeding options.