Delprat Garden in Mayfield North is open to the public this weekend

Delprat Garden, built on the former BHP site in Mayfield North, tests how different plants absorb toxins in contaminated dirt.

It is a step in understanding how phytoremediation - using plants to break down contaminants - can help revive the Hunter's soil.

The joint venture between the University of Newcastle (UON) and the University of Technology Sydney (UTS) began four years ago and includes a meadow, orchard and cottage garden along with vegetables and natives.

UON's head of the School of Architecture and the Built Environment, Professor SueAnne Ware, said the team aimed to test plants popular in Newcastle gardens.

"We walked a lot around Mayfield East, Mayfield and Tighes Hill just to see what people were planting around their houses," she said.

The orchard is full of magnolias and crepe myrtles as a result.

Professor Ware hoped vegetable testing would allow backyard gardeners to understand their soil and harvest more crop.

She said tomatoes are poor at absorbing toxins, making them hearty growers and safe to eat. Legumes, like carrots, hold contaminants in their roots and may not survive in contaminated dirt.

"In the garden, you can't really control the amount of toxins or growth conditions. You get very different results than, say, a lab would. We [have been] quite amazed," she said.

And it's not just toxins the team are testing. Some plants, like hydrangeas and kangaroo paws, are used for understanding acidity levels.

Hydrangeas are a warm blue in more alkaline conditions and pinken with acidity.

"Litmus plants are quite interesting because you don't always [know what to] expect," Professor Ware said. "Last year our kangaroo paw, which is just a generic garden variety, went mental."

Much of Newcastle's dirt is contaminated from coal dust, defence bases and primary industry. Professor Ware said the best things gardeners can do are get their soil tested and plant in stilted garden beds.

"We're very committed to open source. We put all the different things we discover on our website so they home gardener can go and learn," she said.

Delprat Garden is open to the public 10am to 4pm on Saturday March 4 and Sunday March 5.

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