Gum Tree Eucalyptus robusta

Wet feet finish off most eucalypts. Swamp Mahogany is the exception, and it turns up on coastal drainage lines, in soggy back corners and right through revegetation work on ground that floods. It is easy to pick: thick, soft, spongy red brown bark persisting well out along the branches, and large, broad, glossy dark green leaves that build a heavier and more genuinely shady canopy than most gums manage. Big cream flowers through the cooler months are a serious nectar source on a forest sized tree.

Wet coastal ground, with frost as the limit

It comes from the coastal swamps of eastern Australia and tolerates periodic inundation, and even slightly brackish conditions, that would kill a spotted gum. That makes it a natural fit for coastal New South Wales, south east Queensland and warmer coastal districts of Victoria and South Australia, particularly on flats that go under after heavy rain. Full sun, and it will take heavy clay without preparation. Flowering in the cooler months matters ecologically, because it feeds lorikeets, honeyeaters and flying foxes at a time of year when little else is producing nectar. In a windbreak, space for a broad, dense crown rather than a narrow one.

Frost sets the boundary, and inland buyers miss it. Young plants are damaged by hard frost and a bad winter on a cold flat will cut them back or kill them outright, which is exactly the site people choose because it is the wettest part of the property. Cold air pools in those hollows. If your winters bring regular heavy frosts, plant something else on that ground rather than replacing losses each spring.

Swamp Mahogany among the wet ground trees

For wet ground, flat topped yate is the frost tolerant, salt tolerant alternative out of Western Australia, and it is the one to use on a saline inland flat. Flooded gum holds damp clay on the Swan Coastal Plain but has its own pest problems in urban gardens. Swamp Mahogany carries the broadest leaves and the densest canopy of the three, so it is the one you can actually stand under, and its cool season nectar makes it the most useful of them for habitat work along the east coast. The flowering season is a real point of difference as well, since it produces heavy nectar in the cooler months when the other two have finished. Choose it for warm, wet, frost free coastal ground where shade quality is the point. Larger sizes are in mature trees.

Let the crown build itself

Prune in late winter or early spring, before growth moves. Structural work is limited to the first few years, selecting a leader and shortening competing stems, after which it can be left to build its own canopy, because the broad crown is what makes it useful. Remove deadwood and anything overhanging a roof. Feeding is barely necessary on damp fertile ground. One feed a year while it is young, from a native range product, is enough. Mulch, keep grass off the trunk, and keep it well away from sewer lines and tanks, because the roots chase moisture hard.

Choosing a size

This plant is available in 4 sizes, from 140mm up to 100L, priced from $16.95 to $2189.00 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 Australian native trees for shade.