A slope is a different design problem to flat ground. Water moves differently, soil moves differently, and trees do far more than decorate. They lock things in place.
Pick a tree built for slopes and plant it right, and the planting holds the line for decades with very little ongoing work.
What slope sites need from a tree
Deep or fibrous roots that anchor soil. Tolerance for fast-draining ground at the top of the slope. Comfort in damper ground at the bottom. And enough toughness to handle wind and exposure.
Five trees that meet that brief.
River Sheoak
The Casuarina is the unofficial slope tree of Australia. Deep roots, soft weeping needles and serious tolerance for poor soil and seasonal water. Plant in groups of three to five on the contour for stronger anchorage.
Lime Magik Wattle
For the soft edge of a slope or the top of a retaining wall. Compact, weeping and a fast cover plant with fibrous roots that knit soil together. Mass plant 1m apart.
Coast Banksia
Built for tough ground. Holds in sand, holds in coastal wind, holds on exposed slopes. Bonus: a long winter food source for native birds.
Sweetgum
For larger slopes that can take a deciduous giant. Deep root system, fast growth and one of the most reliable autumn colour shows in the country.
Pin Oak
The classic country slope tree. Strong taproot, broad pyramidal canopy, scarlet autumn colour. A long-term investment for properties with the space to host it.
How to plant on a slope
Plant on the contour, not down the slope. Build a small berm on the downhill side of each tree to catch water. Mulch heavily out to the drip line and water deeply through the first two summers.
Combining trees on a slope
Layer the planting. Tall trees at the top, screens in the middle, dense ground cover at the bottom. Each layer slows water and stabilises soil. The Casuarina screen with a Lime Magik ground layer is a tested combination for steep, exposed sites.
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