Nearly 100 cities now divert food waste from landfills. It’s far from becoming the norm, though, considering most major cities still don’t even have curbside recycling.

One million tons: That’s the amount of compostable organic waste San Francisco has collected since its composting program began more than 15 years ago. But things really started piling up just three years ago, when the city mandated composting for all city residents and businesses. Today, San Francisco collects 600 tons a day as part of its overall effort to achieve zero waste by 2020.

San Francisco may have been the first major U.S. city to mandate composting, but it is no longer the only one. Curbside composting has experienced unprecedented growth over the last three years. There are now more than 90 cities with such programs, according to Bruce Walker, solid waste and recycling program manager for the Bureau of Planning and Sustainability in Portland, Ore. Portland launched its curbside composting program in October, joining the likes of Boulder, Colo.; Salem, Ore.; and Seattle, among other cities.

The motivation behind these programs is simple: maxed-out landfills. Americans generate 250 million tons of garbage per year. Before San Francisco started its composting program in 1996, a city study found that more than one-third of all waste entering landfills could be composted instead. Today, between composting and recycling, the city diverts 78 percent of its waste from landfills. When Portland launched its composting program, it cut back its weekly garbage collection to every other week. Customers just weren’t producing as much trash.

Portland’s original pilot program, according to Walker, found that customers were “generating 30 percent less garbage every month.”

Ultimately, San Francisco and other composting cities have found that it is cheaper to compost than dump garbage, because it extends the life of landfills by saving space. Diverting food waste from landfills also reduces carbon emissions and the risk of potential groundwater pollution. Plus, the end product of composting can be reused and resold as fertilizer.

But curbside composting is likely years off for most municipalities. Most major U.S. cities still don’t even have curbside recycling programs. Nationwide, the recycling rate is only 33.8 percent — 3 percent of which represents composting of food waste — according to the Environmental Protection Agency.

Portland estimates that its composting program cost about $1 million to set up — most of which has been spent on education efforts explaining how and why to compost. Advocates say those efforts shouldn’t be overlooked: If residents don’t know why they should be saving organic waste, they’re far less likely to do so.