She-Oak Casuarina cunninghamiana

River she-oak lines watercourses up the eastern side of the continent, which explains how it behaves in cultivation. What look like pine needles are fine jointed branchlets, the true leaves reduced to rings of tiny teeth at each joint, so the canopy filters wind instead of blocking it and makes a sound in a breeze that no other tree here matches. It grows fast into a tall upright tree with fibrous roots that bind friable soil. Shelterbelts, creek frontages and screening on acreage are where it belongs.

Branchlets, not needles

Full sun and moving air suit it, and once established it needs little water, but the position that really shows it off is ground that gets wet. It handles sandy alluvial flats, creek banks and sites that flood occasionally, tolerates frost, and copes with salt wind on the coast. Like other she-oaks it works with soil bacteria to fix its own nitrogen, so poor ground is not an obstacle. For a shelterbelt, set trees roughly three metres apart in the row, and tighten that to about two metres if you want a dense screen, accepting that the trees will thin at the base as they climb. The failure mode is scale. This is a forest tree with a large root system, planted far too often in small suburban backyards, and the shed branchlets build into a thick mat that suppresses lawn and most understorey planting beneath it. On acreage, along a boundary or in a windbreak, that is exactly what you want. In a courtyard garden it becomes a removal bill.

Permanent shelter against a quick nurse crop

Silver wattle is the other fast native windbreak in this batch, and the choice between them is about time. The wattle covers ground sooner and flowers, but it is short lived and brittle, so it works as the nurse crop that shelters the she-oak while the she-oak grows into the permanent shelter line. Plant both and take the wattles out as they decline. Scale is the other divider, because the she-oak is a full sized forest tree and the wattle is not, so on a suburban block the wattle is often the only one of the two that fits at all. On the salt front itself neither is the answer; Pandanus pedunculatus holds a foredune position that would burn a young she-oak. Other screening options sit in privacy screening.

Shaping a young she-oak

Prune young trees for structure rather than shape. Pick a single leader early, take off competing leaders and any tight forks while the wounds are small, and lift the lower branches over several seasons if you need clearance underneath, working in late winter before the spring flush. Do not top an established tree, because it answers with weak, crowded regrowth. Feeding is rarely necessary given the nitrogen it fixes for itself, and if you do feed young trees on poor sand, use a low phosphorus native fertiliser in spring and keep it off the trunk. Mulch the root zone while the tree establishes, and keep line trimmers away from the bark on young stems.

Choosing a size

This plant is available in 11 sizes, from 70mm up to 200L, priced from $16.95 to $999.00 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 fast growing screening plants.