Tree Fern Cyathea australis (Alsophila)

Rough tree fern and soft tree fern get sold to the same buyers and they are not interchangeable. Cyathea australis carries a slimmer, darker trunk and stiffer, more upright fronds, and the frond bases feel harsh and scaly in the hand, where Dicksonia antarctica is fat trunked and wrapped in soft brown fibre. It grows in gullies and wet forest down the east coast, from Queensland through New South Wales and Victoria to Tasmania. Use it for fern glades, shaded courtyards and the understorey beneath established trees.

The rough tree fern

This is the tree fern for a cold garden. It handles frost and cool highland conditions better than most of the group, which makes it workable well south of where the subtropical species give up. Soil should be deep, crumbly and full of organic matter, kept damp through summer and mulched heavily; leaf litter and compost around the base do more good than fertiliser ever will. Water into the crown and down the trunk as well as onto the ground, because the trunk carries roots that take up moisture directly. Shelter from hot dry wind matters more than anything else you can give it. The failure mode is drying out. A run of hot days with the crown left dry will crisp the fronds and kill the growing point, and there is no recovery from that: unlike Dicksonia, a Cyathea trunk cannot be cut and replanted, so a dead crown is a dead plant. Set the irrigation up before summer rather than after the first heatwave. Plants growing under an established canopy hold moisture longer between waterings and take less wind, which is why gully plantings look after themselves.

Rough or smooth, cold or coastal

Cyathea cooperi is the obvious comparison and the differences are practical. Cooperi has pale, finely divided fronds, a slim trunk patterned with neat oval scars and a subtropical constitution; australis is coarser, darker and much tougher in the cold, and it is far less likely to seed itself around your garden. Take cooperi for a warm coastal courtyard where you want soft texture, and australis for a Victorian or tablelands garden, a frost pocket, or a gully planting that has to survive without babysitting. For a tender rainforest palm at the other end of that range, see Schippia concolor. Both tree ferns are sold on trunk height, so compare trunks rather than frond spread when you are matching sizes. More of the group is under ferns.

Old fronds and gentle feeding

Cut fronds off only when they have browned right through, close to the trunk but without gouging it, and leave anything still holding green tissue because the plant is still drawing on it. Late winter and early spring, before the new croziers unfurl, is the tidiest time to do it. Wear long sleeves; the scales on the frond bases irritate skin. Feed lightly in the warm months with a dilute liquid fertiliser or aged manure spread over the root zone, never a strong dry fertiliser tipped into the crown, and keep the mulch layer deep. Fronds that brown from the tips inward through summer are almost always a watering problem rather than a feeding one.

Choosing a size

This plant is available in 5 sizes, from 140mm up to 100L, priced from $16.95 to $649.00 per plant. The size shown is the pot the plant arrives in, which is the rootball, not the height of the plant. The smaller pots hold younger plants that cost less each and establish quickly, which suits hedges, screens and mass planting where the plant count adds up. The larger sizes carry several more years of growth on the farm and give height and presence straight away, which is what you want for a single feature position or a screen that cannot wait. Not sure which to choose? Read our guide to when to plant in Australia.