The perfect storm of the arrival of autumn and falling leaves, coupled with more people working from home during the pandemic, also saw the average number of green waste bins collected increase by almost 5700, from 20,835 in February to 26,529 in April.

The average amount of green waste collected grew from 303 tonnes in February this year to 384 tonnes in March, as the social distancing restrictions kicked in, to 504 tonnes in April.

The presence of more people at home and using the green waste service prompted a reminder to residents not to contaminate their bins by putting banned items in them, such as plastic bags, cardboard, large logs and stumps, food waste and processed timber.

The green bins are only meant for garden waste such as grass clippings, weeds, leaves, small prunings and flowers.

EnviroCom green waste education officer Jules Watson said most people did the right thing.

"There's definitely been a big increase in people using their bins, because more people are at home and, unfortunately [due to job cuts], some people have more time on their hands," he said.

"The garden might have been neglected and everyone is getting stuck into it, which is really great to see.

"In terms of what's going in the bins, it's nothing that different to the past. One of the main problems we have is plastic bags."

Mr Watson said a lot of people used plastic bags to collect leaves or clippings but then put them in the green waste bins, which was not allowed.

"It's an ongoing battle, but for the most part, more than 99 per cent of Canberrans get it right."

After a series of rolling starts, the green waste collection service was made available to all Canberra suburbs by April last year. More than 14,000 tonnes of green waste have been recovered for conversion into mulch products.

The green waste is taken to the Mugga Lane tip, where Corkhill Bros converts it to mulch for sale to the public. A spokesman for Corkhill Bros said it had not come across anything untoward in the waste.

Mr Watson said some staff handpicked contaminants such as plastic bags out of the waste, and machinery, including a vacuum, could suck out smaller contaminants.

"A lot of waste goes up there, so it's not humanly possible to get everything out," he said. "The first line of defence is really the drivers. If they see any contamination in or poking out of the bin, they just won't flip it. It's our role as educators to go around to residents and let them know what happened."

Mr Watson said things such as treated timber and food waste were not allowed in the green bins as they wanted a clean mulch to put back on gardens.

"You get back what you put in," he said.