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By Phil Burkitt
Local Hawkesbury residents are being warned that the familiar Sweet Pittosporum
(Pittosporum undulatum), once prized for its glossy leaves and fragrant white flowers, may be doing more harm than good in our bushland. While native to the Sydney region, the species has now earned a reputation as an environmental weed in parts of the Hawkesbury.
Pittosporum undulatum is fine as a native forest plant of the deep gulleys but has recently spread and is now quickly outcompetes other native plants in some ares in the Hawkesbury region. Its dense canopy shades smaller plants, and its leaf litter chemically inhibits growth underneath, which can fundamentally alter bushland ecosystems.”
Why Pittosporum is a Weed
The tree grows up to 15 metres tall and can form a canopy up to 10 metres wide. It thrives in disturbed soils, gullies, and moist areas, rapidly colonising spots where native vegetation struggles. Birds help spread the tree further, carrying its bright orange berries and sticky red seeds across the landscape.
While the tree provides habitat for possums and other native animals, it can also dominate native forests, creating monocultures and reducing biodiversity. Bush-regenerators see it taking over areas where our native ground flora should be, it’s beautiful, but it can’t be left unchecked.
Environmental Impacts
Habitat Alteration: Dense stands of Pittosporum shade out native plants and reduce food and shelter for local wildlife.
Ecological Changes: Its rapid growth and leaf chemistry change the soil and forest
composition, sometimes even supporting other invasive plants.
Managing Pittosporum in the Hawkesbury
Residents are advised not to plant Pittosporum near bushland. For existing trees, management includes careful pruning after flowering and removal of seed heads to reduce spreading.
“In bushland areas, a staged removal approach can be best, you don’t want to remove every tree at once because it can shock the ecosystem. A ‘one in three’ or ‘one in four’ strategy over time works well.”
A Tree with Dual Roles
Despite its weed potential, Pittosporum still has important benefits. Its flowers are highly fragrant, and the tree provides important habitat for possums and birds of prey, including Powerful Owls. Gardeners who want a similar aesthetic without the ecological risk can consider alternatives such as lilly pillies or native rainforest laurels.
Pittosporum undulatum’s story is a reminder that even native plants can become a problem when conditions change. Urban development, nutrient-rich runoff, and the absence of natural bushland fires have allowed this species to flourish beyond its traditional range.
Hawkesbury residents are encouraged to enjoy the tree responsibly and always consider the broader environmental impact when planting near bushland.
