The seven-year-old doesn't remember planting this particular tree in Roseville at the age of three, but Laurence is responsible for at least a few other saplings around the city.

"I've done it heaps of times on other tree days, and I go to bush care with my dad," he said.

"It's just fun just going out there and getting dirty and helping nature grow."

This year, event organiser Planet Ark is expecting about 300,000 people to plant 1.1 million trees on Schools Tree Day and National Tree Day, held on Friday and Sunday respectively.

Nearly 2400 schools and 750 council and community groups will hold events across Australia, offering plants and gardening guidance to everyone from toddlers to 90-year-olds.

More than 23 million trees have been planted since National Tree Day was first launched 20 years ago by actor Olivia Newton-John.

The initiative aims to "bring native trees back to the Australian environment", said Planet Ark chief executive Paul Klymenko, who was involved in the 1996 event.

"I remember it well. My daughter Gabby and I planted trees ... and we've done so every year since," Mr Klymenko said.

Horticulturalist and Barcoo Barambah Parkcare co-ordinator Joanna Dodkin-Smith said the event had changed the landscape in her reserve.

"We're now seeing local indigenous species being planted that are far better suited to the environment and better for maintaining wildlife," she said.

"The value of National Tree Day is immense because it really instils the importance of nature.

"For Laurence to be able to come back with his kids in 20 or 30 years and say 'I planted that', that sense of ownership is really important."

Laurence's father, Cameron Bennell, said his family had been "guerilla gardening" for years but the community aspect of National Tree Day made it appeal to the young and old.

"The house we planted the trees outside [in 2012], there's a lady who's lived there for 60 years. She was kind of sceptical they would survive because it was on a nature strip, but of course they did, and she looked after them.

"When we went back, she remembered [Laurence] being so little and she was going, 'Look how big he is, look how big the tree is!'

"A lot of tree planting is away in bush or parks ... but with this, people have that kind of ownership, driving down the road they go 'oh, that's the tree we planted'."