Hamilton will soon ban residents from putting grass clippings and yard waste in their green bins as part of an ongoing effort to reduce smelly compost.

That ban will last for about six months as the city upgrades a composting facility it shut down earlier this year because of the stench. The city will spend the next six months prepping residents for the ban, which will come into effect on April 1.

Residents will still be able to put yard waste in paper bags. But when grass clippings go into compost, it creates ammonia, says Craig Murdoch, the city's director of environmental services. And that creates a stink.

"There will be a period where a ban will have a positive impact," Murdoch told city council's public works committee Monday.

The problem dates back to 2016. That's when the province passed new regulations saying compost needed to be 40 per cent moisture when cured.

Right away, residents downwind of the Central Composting Facility at 1579 Burlington St. E. noticed a putrid smell, says Coun. Sam Merulla. Residents stayed indoors and shut their windows to avoid it.

The city temporarily shuttered its facility, operated by Aim Environmental Group, on June 24. It remains closed, and all organic waste goes to the Glanbrook landfill. Since of Aug. 30, that's amounted to about 5,700 tonnes of material.

Meanwhile, the city is waiting for the province to approve some solutions, Murdoch said. That includes new carbon filters and stack extensions.

Murdoch said the city is pushing the province to move faster. But even when that approval comes, it will take until late next year for them to become fully operational.

So a temporary ban, he said, will "ensure the grass, leaf and yard waste doesn't negatively impact the facility."

The facility itself will become slowly operational again in November, Murdoch said. The city will hire a third-party company to process the waste. In the long term, Merulla said, he wants the facility moved right out of his ward.

The city will spend $50,000 educating residents about the ban. During the ban, residents can still use their green bins for food waste and soiled paper products.

City council still has to ratify the decision at a meeting on Sept. 26.